Time perception associated with durations from 1 s to several minutes involves activity in the right posterior parietal cortex (rPPC). It is unclear whether altering the activity of the rPPC affects an individual’s timing performance. Here, we investigated the human timing performance under the application of transcranial direct-current stimulation (tDCS) that altered the neural activities of the rPPC.We measured the participants’ duration-discrimination threshold by administering a behavioral task during the tDCS application. The tDCS conditions consisted of anodal, cathodal, and sham conditions. The electrodes were placed over the P4 position (10-20 system) and on the left supraorbital forehead. On each task trial, the participant observed two visual stimuli and indicated which was longer. The amount of difference between the two stimulus durations was varied repeatedly throughout the trials according to the participant’s responses. The correct answer rate of the trials was calculated for each amount of difference, and the minimum amount with the correct answer rate exceeding 75% was selected as the threshold. The data were analyzed by a linear mixed-effects models procedure.Nineteen volunteers participated in the experiment. We excluded three participants from the analysis: two who reported extreme sleepiness while performing the task and one who could recognize the sham condition correctly with confidence. Our analysis of the 16 participants’ data showed that the average value of the thresholds observed under the cathodal condition was lower than that of the sham condition. This suggests that inhibition of the rPPC leads to an improvement in temporal discrimination performance, resulting in improved timing performance.In the present study, we found a new effect that cathodal tDCS over the rPPC enhances temporal discrimination performance. In terms of the existence of anodal/cathodal tDCS effects on human timing performance, the results were consistent with a previous study that investigated temporal reproduction performance during tDCS application. However, the results of the current study further indicated that cathodal tDCS over the rPPC increases accuracy of observed time duration rather than inducing an overestimation as a previous study reported. Time perception is indispensable in our daily life. It is a brain function that is necessary not only when synchronizing the timing and rhythm of action but also in many other daily activities, such as controlling the human body to move correctly , perceivThe parietal brain region is generally considered to be associated with many brain functions such as spatial representation, attention and memory –8, and tSeveral studies have shown that the right posterior parietal cortex (rPPC) is one of the areas responsible for the perception of the temporal duration of interval timing, which is a duration range of approximately 1 s to a few minutes. Those studies include brain imaging studies , 14, 15,Many behavioral and cognitive investigations have used transcranial direct-current stimulation (tDCS) to explore whether changes in brain activities affects behavioral and cognitive performance. With the use of a weak constant electric current, tDCS provides noninvasive brain stimulation that enhances or inhibits the neural activities in a particular brain area of interest , 22. SevIf it is found that the change in neural activity affects the performance of a behavioral task, it can be speculated that the stimulated brain region has a relationship with the brain function necessary for performing the task. It had been proposed that anodal tDCS enhances cognitive performance because it causes an excitation of neural activities, whereas cathodal tDCS degrades cognitive performance because it inhibits neural activities. However, this concept has been challenged by several studies –28. For precision, which indicates how large the reproduced duration varies across the trials. Note that the value of precision is irrelevant to the difference between the standard duration and the mean reproduced duration. Vicario et al. reported that the participants overestimated the standard durations when cathodal tDCS was applied over the rPPC. This conclusion was based on data showing that the mean reproduced duration under the cathodal tDCS condition was longer than those of the anodal condition and the sham condition. They did not report that the precision of reproduction was affected by the tDCS over the rPPC in any tDCS condition.Human time perception research has begun to use tDCS to investigate whether changes in brain activities affect timing performance. Vicario et al. (2013) showed that cathodal tDCS over the rPPC affected participants’ performance of a temporal reproduction task . In thataccuracy of reproduction, which indicates how close they are between the reproduced duration and the standard duration. From the viewpoint of the difference from the standard duration, it can be said that the reproduced duration in the cathodal condition was almost the same as the standard duration, whereas that of the anodal condition and the sham condition were quite shorter than the standard duration. Therefore, these results could also be interpreted as indicating that the participants reproduced the duration more accurately when cathodal tDCS was applied. However, it was unknown in that study whether tDCS affects the accuracy of subjectively perceived temporal duration, and for this reason further research is needed to investigate this effect of tDCS.The study of Vicario et al. showed that cathodal tDCS over the rPPC led an overestimation, comparing the cathodal condition against the sham condition; however, it did not show the results of comparison between the mean reproduced duration and the standard duration. This comparison is to evaluate the In the present study, to measure the accuracy of timing performance while tDCS was applied over the rPPC, we used a temporal discrimination task to determine the participants’ duration-discrimination threshold. The duration-discrimination threshold is the minimum difference in temporal duration that can be perceived by an observer. A small duration-discrimination threshold is equivalent to a high temporal discrimination performance and therefore to a high timing performance. In the temporal discrimination task trial, each participant observed two visual stimuli and answered which one was presented for a longer duration. We knew that when the two durations are sufficiently different, a participant will perceive the difference and can thus distinguish the two durations. However, if the difference between the two durations is less than the duration-discrimination threshold, the participant will no longer be able to distinguish between the two durations.In the temporal discrimination task, the difference between the two durations was changed for each trial, and the participant repeated the trial until the threshold could be estimated from the participant’s responses. It is plausible to regard a lower threshold as a higher ability and higher accuracy of timing performance. If the duration-discrimination threshold is low, the participant can distinguish smaller time duration differences and should thus be able to more accurately reproduce the standard duration when performing a temporal reproduction task.As long as focusing temporal discrimination performance, a temporal discrimination task has advantages over a temporal reproduction task. When an individual’s timing performance is measured with the use of a temporal reproduction task, the duration provided by the participant can vary greatly because the range of response durations is not limited. In other words, the participant can generate arbitrary durations as the reproduced duration, which can cause significant variations in the measurement of reproduced durations. The temporal discrimination task can reduce the variability of the participant’s response because it only requires the participant to indicate the longer one from two durations. Instead, the participant performs trials repeatedly, and the threshold is calculated from data of the entire task. In addition to the advantage described above, there is another advantage that the temporal discrimination task does not require precise physical motor manipulation. In the temporal reproduction task, participants press a push button by the same length as the standard stimulus duration, and thus, the participants need to precisely manipulate their hand in order to press the push button at accurate timing. This property of the temporal reproduction task may cause a confusion between the effects of tDCS because the tDCS may affect both the observation of the stimulus duration and the precision of physical motor manipulation.Nineteen healthy volunteers participated in this study . We excluded three participants from the analysis: two who reported extreme sleepiness while performing the task, and one who could recognize the sham condition correctly with confidence. Their data showed extremely high thresholds or large variation between conditions, and thus, we considered they should be excluded from the data analysis. For this reason, the data from the remaining 16 participants  were used for the further analyses.All participants had normal or corrected to normal vision. They were all right-handed (handedness score 90.0 ± 9.1 SD), as confirmed by the Edinburgh Handedness Inventory . We explWe used a battery-driven current stimulator  to generate and control the direct-current stimulation. The current was delivered through a pair of sponge electrodes placed on the surface of the scalp. The sponge electrodes were soaked with weak NaCl solution. It was reported that participants feel more comfortable when the electrode solution has a lower concentration (15 mM) compared to a higher one (140 mM) . We ther2) was placed over the P4 position defined by the International 10–20 system. According to a study that investigated the relationships between the positions of the cortical regions and the scalp surface by using structural high-resolution MRI [The stimulus electrode  was mounted on the contralateral (left) supraorbital forehead. Several tDCS studies have used a return electrode placed on the supraorbital forehead on the side contralateral to the stimulus electrode [The return electrode . The polarity in the condition name was matched with the polarity of the stimulation electrode. In the anodal and cathodal tDCS conditions, the electric current was applied from 5 min before the start of the task to the completion of the task. The intensity of the electric current was 2 mA. In order to reduce the sensation from the current, we gradually ramped up the current for 5 s at the start of the current application and ramped it down at the end of the current application. The current stimulus applied before the start of the task had sufficient duration and intensity to cause its effect by the start of the task , 37. ForIn the sham condition, the current was applied in a manner that was identical to the two other conditions but was applied only for the first 40 s and never applied again after being stopped, including the task period. The selection of the real/sham condition was double-blinded.In light of the tDCS aftereffect , we had the participants perform each condition on three separate days. In order to reduce the time-of-day effect, which could affect participants’ fatigue and sleepiness, each participant was scheduled to perform each condition at approximately the same time of day . For each participant, the first and the last experimental day were not more than 7 days apart. The order of the three conditions and the polarity of the sham current were counterbalanced across the participants.2) presented by a visual stimulus presentation device that consisted of an LED, light diffuser films, and a light-shielding sheet with a hole of 17.5 mm in diameter. Since the switching of the LED was operated by a microcontroller , the accuracy of the presentation duration was < 0.1 msec. The participant sat on a stool and put his or her chin on a chin rest, with a viewing distance of 55 cm from the visual stimulus. The lighting in the experimental room was dim (5 lx at viewing position), and a gray curtain was attached to the wall behind the visual stimulus presentation device.The visual stimulus was a green-filled circle  by measuring the participants’ duration-discrimination threshold in a temporal discrimination task procedure. Previous studies used this procedure to evaluate their participants’ temporal discrimination performance –42.The task consisted of trials in which the participant compared two durations. At the beginning of the trial, the visual stimulus was presented twice. After this presentation of the visual stimuli, the participant judged which stimulus had a longer duration and indicated it with a push button. If the first stimulus was judged to be longer than the second one, the participant pressed the push button held in his or her left hand, and if the second stimulus was judged to be longer than the first one, the participant pressed the push button held in the right hand. The participant was not informed whether the answer was correct.T) msec, where T was a positive variable. They were presented in randomized order, and the interval from the offset of the first stimulus to the onset of the second stimulus was 1.5 s. The duration-discrimination threshold was measured as the minimum T value that enabled the participant to perceive the difference between the two stimulus durations. When the participant gave correct responses to > 75% of the trials with a specific T value, we considered this T value as a perceivable difference. We calculated the correct answer rate of the trials for each T value, and we selected the minimum T value with the correct answer rate exceeding 75% as the threshold. We determined the thresholds separately for all three tDCS conditions .The two stimulus durations were 1800 msec and . The T value was 600 msec in the first trial. Most of the participants easily distinguished the durations with this T value. Whenever correct responses were observed consecutively over three trials with the same T value, we decreased the T value by 25 msec in the next trial, and whenever an incorrect response was observed, we increased the T value by 25 msec. Until the first switchover from a decrease to an increase, the T value was decreased by 50 msec instead of 25 msec for a quick convergence. The task was terminated when the 12th switch between a decrease and increase was observed. Figure T value in a task performed by one participant in one tDCS condition as an example.In the task, we repeatedly changed the We assessed the effect of tDCS on the duration-discrimination threshold with the use of a linear mixed-effects models procedure. This procedure is suitable for repeated-measures samples, obtained from within-subject design experiments . The datp value to estimate the differences in the mean threshold between the tDCS conditions. We also analyzed the differences in the number of trials and the task duration among the tDCS conditions. These analyses also used a linear mixed-effects model procedure. Based on the AIC value, the diagonal model was selected as the optimal covariance structure model for the analyses of the number of trials and the task duration. The statistical analyses were performed with IBM SPSS Statistics (ver. 19) software .We conducted a post hoc multiple comparison test with the Bonferroni adjusted F = 3.957, p = 0.030). The post hoc test revealed a significant difference between the sham and cathodal tDCS conditions (p = 0.041). No significant differences were detected between the sham and anodal tDCS conditions (p = 1.000) or between the anodal and cathodal tDCS conditions (p = 0.107). The mean values and their standard errors are illustrated in Fig. We analyzed the data obtained from the 16 participants. The mean duration-discrimination threshold value and standard deviation for the three conditions were as follows: sham, 300.0 ± 113.7 msec; anodal tDCS, 287.5 ± 85.6 msec; and cathodal tDCS, 221.9 ± 91.7 msec. We tested the mean duration-discrimination threshold values by the linear mixed-effects model procedure, and the standard error and the degree of freedom were calculated to be 24.434 and 39.841 for each of the tDCS conditions, respectively. Our analysis of the duration-discrimination thresholds indicated a significant effect of the tDCS conditions  = 2.372, p = 0.108).The average number of trials and standard deviation were as follows: sham, 70.0 ± 12.9; anodal tDCS, 71.5 ± 8.0; and cathodal tDCS, 79.4 ± 13.9. Based on the analysis results, the standard error for the sham, anodal, and cathodal conditions was calculated to be 3.217, 2.000, and 3.480, respectively, and the degree of freedom was 15.000 for all conditions. We analyzed the differences in the trial number among the tDCS conditions by the linear mixed-effects model procedure, and it detected no significant differences  = 2.582, p = 0.093). The duration of the tDCS application did not exceed 20 min for all participants in all tDCS conditions.The average duration of the task and standard deviation were as follows: sham, 569 ± 100 s; anodal tDCS, 578 ± 55 s; and cathodal tDCS, 649 ± 121 s. Consequently, since the duration of tDCS application was 5 min longer than the task duration, the mean durations of tDCS application were 14 min 29 s, 14 min 38 s, and 15 min 49 s, respectively. Based on the analysis results, the standard errors for the sham, anodal, and cathodal conditions were calculated as 24.955, 13.806, and 30.287 s, respectively, and the degree of freedom was 15.000 for all conditions. The analysis of the task duration indicated no significant differences  that investigated the effects of tDCS on their participants’ temporal reproduction performance, the participants were instructed to reproduce the same duration as the standard duration during tDCS application . VicarioContrary to the previous findings that cathodal tDCS has an inhibitory effect since it decreases the neural firing frequency –24, the Our present findings are consistent with these studies, which showed that cathodal tDCS does not always impair cognitive performance and can even improve brain function. Our results can thus be interpreted as indicating that cathodal tDCS enhances the excitability of the rPPC and leads to an improvement in timing performance.However, it is unknown whether inhibition of neural activity always impairs brain function. For this reason, we can also hypothesize that the timing performance was enhanced despite the inhibited neural activity of the rPPC resulting from the decrease in the neural firing frequency caused by the cathodal tDCS. As an explanation of why inhibition of the rPPC resulted in enhanced timing performance, we speculate that an inhibition of neuronal firing in the rPPC decreased attentional distractibility and thus enhanced the temporal discrimination performance. This speculation is based on the previous findings that the parietal brain region is related to the function of directing attention and attentional distractibility. Several studies showed that the rPPC is involved in directing attention to an object in the environment –11. HayaSince the volume of the gray matter of the parietal region is related to the degree of attentional distractibility, we speculated that the neural activity in the parietal region is related to the function of directing attention to other objects. If this speculation is true, it may be possible that when cathodal tDCS suppresses the neural activity in the parietal region, the attention of the participant is steadily directed to the task and it is difficult to direct attention to other objects. In addition, this notion is supported by an evidence that anodal tDCS over the rPPC improved the participants’ attentional capability and their visuospatial performance to detect visual stimuli located across the visual field . This evWe observed the effect of cathodal tDCS on temporal discrimination performance, but we did not observe the effect of anodal tDCS. This is in agreement with the study by Vicario et al. (2013), which showed that cathodal tDCS affects participants’ time reproduction performance, while the effects of anodal tDCS were not detected. Although it remains unclear why no effects of anodal tDCS were observed in the present study, we suggest several hypotheses.The first is that the size of the effect might depend on the current’s direction, i.e., the cathodal tDCS remarkably decreased the neural firing rate whereas the anodal tDCS did not cause much of an increase. For example, if the cells had already been firing at a relatively high frequency, it is possible that anodal tDCS did not increase the neural firing frequency much. This might be influenced by physical factors such as the relationship between the firing threshold potential and the resting potential and the ionic balance between the inside and the outside of the neuronal cell membrane –47.A second possibility is that the neural firing rate actually increased but did not greatly affect the capability of directing attention. In other words, changes in directing attention capability might be more sensitive to a decrease of neural firing frequency than to an increase. There might be a ceiling effect that makes it impossible for the anodal tDCS to further enhance the capability of directing attention. It is also possible that changes in the threshold were not detectable in the current task due to their slightness even though the anodal tDCS did actually affect the capability of directing attention.A third possibility is that the anodal tDCS affected the capability of directing attention but the amount of attention increased equally for all objects, including peripheral objects and the task itself. If the anodal tDCS enhanced the capability of directing attention, it could result in an increase in the amount of attention to the periphery, but simultaneously, it might also cause an increase in the amount of attention to the task itself. It can thus be speculated that the effect of the anodal tDCS was not detectable because the relative amount of attention to the periphery was not changed. In relation to this possibility, it was reported that anodal tDCS over the rPPC improved the participants’ attentional capability and their visuospatial performance to detect visual stimuli located across the visual field . This fiAlthough we suggest some of the possible explanations listed above, the present study did not use a task to measure attentional allocation or distraction. For this reason, further research is needed to confirm the validity of the above-described hypotheses and to address the remaining unclear points regarding the precise mechanism by which tDCS affects human brain function.T value started from a large value and decreased until it reached the threshold. As a consequence of the nature of the task, there was a tendency for more trials to be required to reach a low threshold, which was largely different from the initial T value. For this reason, even if there was a tendency for a change in the number of trials, it is still appropriate to conclude that the cathodal tDCS lowered the participants’ duration-discrimination threshold.In the present study, the number of trials depended on the participant’s responses, so that the task duration was not controlled by the experimenter. Although there were no significant differences in the number of trials or the task duration, the data showed tendencies for differences between the conditions. Apart from statistical significance, the cathodal condition seemed to have more trials and a longer task duration compared to the two other conditions. Considering this together with the other results, the lower threshold tended to be associated with a larger number of trials. The reason for this is the nature of the task, i.e., the 2) was larger than that of the stimulus electrode (5 × 5 cm2) so that the density of the current that passed through the return electrode was smaller than that of the stimulus electrode. For this reason, the current near the return electrode was less effective than the current passing through the stimulus electrode, and thus, it is more reasonable to conclude that the results in the present study were caused by the change of activity in the rPPC, which the stimulus electrode was placed over.The tDCS return electrode was mounted on the contralateral (left) supraorbital forehead in the present study according to the previous studies. This might result in a confounding effect that tDCS could stimulate the location that the return electrode was placed over. However, the area of the return electrode (5 × 7 cmWe cannot positively assert that the current affected only the rPPC and therefore need to consider the relationships between brain-area function and task property, as well as the electrode position. In light of the many previous studies that revealed the relationship between the rPPC and human temporal performance, however, it is plausible to consider that the tDCS affected rPPC and resulted in enhanced temporal discrimination performance.In summary, we investigated human time perception from the viewpoint of brain activity by administering tDCS and found a new effect that cathodal tDCS over the rPPC enhanced temporal discrimination performance. In terms of the existence of anodal/cathodal tDCS effects on human timing performance, our results here were consistent with those of a previous study that investigated temporal reproduction performance during tDCS application. However, our results further indicated that cathodal tDCS over the rPPC increased accuracy of observed time duration, rather than inducing an overestimation, as was reported in a previous study. Although we observed that cathodal tDCS enhanced temporal discrimination performance, the mechanisms underlying this effect remain unknown. Confirmation of the validity of the hypotheses we have described herein requires further research including measurements of brain functions other than temporal perception, such as spatial representation, memory capacity, and attentional allocation and distractibility.


A new sensor for estimating elasticity of soft tissues such as a liver was developed for minimally invasive surgery application.By measuring deformation and adjusting internal pressure of the pneumatic sensor head, the sensor can be used to do palpation (indentation) of tissues with wide range of stiffness. A video camera installed within the sensor shell is used to register the radius of the contact area. Based on finite element model simulations and the measured data, elastic modulus of the indented soft tissue can be calculated.Three phantom materials, namely plastic, silicone and gelatin, with varied stiffness were tested. The experimental results demonstrated that the new sensor can obtain highly reliable data with error less than 5%. The new sensor might be served as an instrument in laparoscopic surgery for diagnosis of pathological tissues or internal organs. Ongoing improvement of medical equipment enables an invention of new less traumatic surgical instruments called minimally invasive surgery tools. One of the first operations using minimally invasive surgery tools was performed in 1901 by Ott, who is known as one of the pioneers of laparoscopy , 3 and uAnother method , based oA device can be used to estimate a density of tissues and the data can be transmitted to a tactile display. Palpating the display, a surgeon can feel a density of examined tissue . AnotherHowever, the above mentioned methods do not quantitatively determine mechanical properties of the internal organs of a patient during a laparoscopic operation. Information about local mechanical properties of soft tissues is necessary for assessing its deviation from that of healthy tissue and for an instant detection of tumors inside an examined organ. New methods have been developed to estimate the mechanical properties of human internal organs. A device proposed for a minimally invasive surgery operation allows determination of the stiffness of tissue . It contThe goal of research , 12 was In this paper we present a miniaturized tactile video sensor, equipped with an optical sensor that allowed measuring displacement of central point of the sensor head, and an air pump that can adjust pneumatic pressure inside the sensor head. Varying an additional air pressure allows us to change sensitivity of the system. Deformation of the tip, contact area and internal pneumatic pressure of the sensor head are measured during the indentation. An Young’s modulus of tissue in consideration is obtained by fitting the experimental data to results of calculation of a finite element model that simulates the indentation process. Tumor detection technique is a subject of our further studies.Three phantom materials with varied stiffness, namely rigid plastic, silicone and gelatin were tested. Gelatin phantom sample was used for imitation of soft biological tissues. The miniature video-tactile pneumatic sensor was developed to measure the contact mechanical characteristics of soft biological tissues. The schematic diagram of the sensor is shown in Fig. The video-tactile pneumatic sensor is based on an airtight cylinder attached at one end to a load cell. A soft silicone shell is fitted at the other end of the cylinder. The cylinder contains a video camera, a non-contact optical proximity sensor, and a light-emitting diode (LED). The LED serves as a light source that adjusts the amount of light inside the silicone shell to enable visualization of the optical image obtained by the video camera. The optical proximity sensor can measure a displacement of the shell tip. For this purpose a miniature mirror (diameter 1.5 mm) is glued centrally on inner surface of the shell.During the experiments, the central part of the shell may be bended inwards when indenting a soft tissue and resulting in a ring shaped instead of circular contact area. To avoid this effect and to ensure a circular contact area, a compressed air was supplied to maintain a constant additional internal pressure measured with a manometer. This adjustable additional pressure inside the silicone head can tune the stiffness of the video tactile sensor and the sensitivity of sensor system. This approach enables measuring an Young’s modulus of soft tissues over a wide range.a (mm) and the displacement of the central point of the shell us (mm) relative to the cylindrical tube of the sensor, which is obtained by the optical proximity sensor . This material demonstrates elastic behavior for the selected load levels. Young’s modulus of PDMS is also measured by the spherical indentation test in previous study  and appematerial   were tested. All three materials were considered as homogeneous and isotropic. The plastic was used as a standard sample for calibrating the sensor. Silicone sample was made from the same material as the sensor head. We assumed this material as linear elastic, with Young’s modulus cated in , modelinTo ensure reliable modeling of a contact interaction between the sample and the shell with pneumatic pressure inside, the problem was divided into two stages. The objective of stage 1 is to determine the shape and stress–strain curve of the shell under internal air pressure before contact interaction. The objective of stage 2 is to determine the contact mechanics.R1 is 5 mm with thickness δ of 0.4 mm. Length of the cylindrical part of the shell l is 4 mm  and the pressure pair on the shell inner surface remains constant. Contact condition can be written in the following form:At stage 2, contact interaction of the deformed shell with the three samples is considered. Refer to the contact scheme in Fig. μ can be specified for each contact pair:The friction forces, calculated according to Coulomb’s law, are taken into account, and the friction coefficient μ are varied in ranges  for PDMS and  for the gelatin phantom.The values of friction coefficient us:h represents the value of the applied vertical displacements on the cylindrical section of the shell.The main contact parameters for calculation are the radius of the contact area and the parameter Both silicone and gelatin samples have cylindrical shape, with 6 mm radius and 12 mm height for silicone one, and 45 mm radius and 7 mm height for gelatin. The problem formulation may take into account friction between the sample and the base. However, calculations demonstrate that the friction, for the selected width of gelatin layer, negligibly affects the size of the contact area. We studied dependences of contact area on deformation of the sensor head for values of the friction coefficient from range (us (“a-us” curves) are calculated for Young’s modulus range from 140 to 260 kPa with an increment of 30 kPa to cover all the experimental data. The value of elastic moduli for gelatin phantom is chosen from the family of a-us curves.To calculate the contact parameters and dependences of contact radius on load ANSYS 14.0 (Academic license) is used. The meshed fragment of the finite element model is shown in Fig. h = 1.7 mm and inside pressure pair = 6 kPa. Figure z of gelatin.The deformed shape of the indenter in contact with the gelatin sample is presented in Fig. After performing experiments the obtained data is depicted on the same plot and the standard deviation from the experimental data is calculated for each calculated curve Fig. . The curus .An analysis of the curves in Fig. a on us for samples with varied stiffness were obtained. A comparison of the calculation results and experimental data is shown in Fig. From the experimental results, dependencies of us for interaction with the glass, silicone and gelatin phantom.A comparison of the experiments and calculation results for the materials with known mechanical properties verified the calculation model. It is shown in calculations that the friction force has negligible effect on the dependence of the contact area size versus the parameter The results show that the model simulation is consistent with the experimental data, and the mechanical properties of gelatin are well simulated by using an incompressible linear elastic model. Young’s modulus of gelatin phantom was determined using the least squares technique by fitting calculated curves with the experimental points and it was found to be 200 kPa. This value is close to elastic modulus estimations obtained for carcinoma , gelatinThe video-tactile pneumatic sensor allows observation of the contact area during the indentation process. The sensor and the methodology for determining elastic modulus of soft tissues ranged less than 200 kPa were developed. One of supplementary advantages of the sensor is the fact that the additional air pressure could be used to tune stiffness of the sensor and to increase its applicability for estimating elastic modulus of tissues within different ranges of values. The sensor can be used for stiffer materials if the additional pressure in the head will be increased. It was also demonstrated that mechanical behavior of phantom may be described by incompressible linear elastic body model.We performed experiments with flat sample surfaces. Biological tissues have largely uneven surfaces. Before testing biological tissue the device should be oriented in such of way that the visible area of contact would be symmetrical about the central point.Future prospects of the method could be as follows: application of the device in laparoscopic surgery, development of the device and theoretical model for tumor locating by generating a map of elasticity in a certain area, and improvement of existing laparoscopic instruments to provide force feedback during the operation.The new sensor can be promising tool for determining elastic properties of tissues such as the liver during laparoscopic operations.


This report is based on an independent study carried out by medical professionals of the Fondazione IRCCS Istituto Nazionale dei Tumori  in Milan, Italy, and  aimed to assess the incidence of respiratory diseases in a Brazilian community  exposed to extreme air pollution in connection to a local steel manufacturing plant. The study has the objective to contribute to the existing literature on the health risks associated with fine particle pollution (PM2.5) due to steel production with data from Brazil.The study is based on a cross-sectional sample of the resident population of Piquiá de Baixo age 16 or over consisting of 220 people. We collected data about the health conditions of participant subjects in two ways: a) medical history questionnaires and b) clinical assessment of respiratory function through spirometry testing. The results were evaluated based on comparative studies.According to the spirometric tests performed, 28 % of the sample population suffers from respiratory pathologies (for the most part of restrictive rather than obstructive nature). This incidence rate is between six and two times higher than those reported in similar studies carried out in other countries (which range between 4.6 and 14.5 %). In addition, the incidence rate is also significantly high in light of the fact that our sample population did not include the category of subjects most at risk for pulmonary disorders in connection to air pollution caused by the Piquiá steel processing complex: in other words, men and women employed in the steel mills or in connection with their industrial cycle (as many as 434 Piquiá residents age 16 and over were unable to participate to our study due to “work-related reasons”).In light of the above considerations, we believe that our findings contribute to the existing literature on the correlation between pulmonary disease and air pollution in industrialized areas, while warranting further scientific research on the public health consequences of industrial production in Piquiá de Baixo. In turn, on the ethical plane, we believe that research of this nature strengthens the need to advocate for more severe environmental and health policies aimed at limiting the hazards associated with the steel industry in Piquiá and in similar contexts around the world. Thanks to sustained efforts in epidemiological research, we now know that: a) high concentrations of particulate matter (PM) in the air we breathe are the primary factor of health hazards tied to air pollution and b) that the finer the particles are , the greater the danger. Most epidemiologists make the case by looking at mortality rates and causes. For example, the American Heart Association has shown time and again that in contexts of environmental pollution due to elevated PM concentrations, people tend to die of respiratory, cardiovascular, and oncological pathologies in greater numbers than normal . LikewisMoreover, research focused specifically on environmental pollution due to industrial production has shown that different industries and manufacturing processes produce particulate matter of different size. When it comes to the steel industry in particular, the literature shows that the processing of iron and other heavy metals, which constitutes the first step of steel manufacturing, produces dust emission with heavy polluting consequences in some area –5.Research focused on industrial pollution from an occupational health standpoint is also of guidance in methodological terms, since it tends to assess risk based on data like respiratory conditions rather than mortality rates. In particular, a number of studies investigating the health hazards tied to occupational dust exposure rely on a combination of medical questionnaires and analysis of lung function through spirometry testing , 7.This approach is especially useful for general population studies based on contexts where death records are either inaccessible or incomplete, for instance due to heavy migration flows. This is precisely the case of our research setting: Piquiá de Baixo, a neighborhood in the city of Açailândia, state of Maranhão, in north-eastern Brazil, where people have shared their vital space with an iron-processing plant tied to the international steel industry since the late 1980s. Faced with resistance from the state and local health board in accessing records and with incomplete information when access was granted, we could not rely on illness and mortality rates to investigate the potential health risks tied to environmental pollution caused by the industrial plant. We thus decided to follow the example of the above-mentioned studies and assess the health conditions of the local population based on medical history questionnaires and the assessment of pulmonary function via spirometry testing, using advanced technology and following the latest international guidelines. The main objective of our investigation is to contribute to the literature on the health risks associated with fine particle pollution  with data from Brazil.The Piquiá de Baixo community, today consisting of about 320 families and 1100 individuals, began taking shape in the 1960s. Close to three decades later, people here suddenly saw a vast area of their neighborhood turn into a major industrial complex tied to the Greater Carajás Program, a government-sponsored project managed by what used to be a national mining corporation, Vale do Rio Doce, today a private multinational company known as Vale S.A. Since its inception in the late 1980s, the project has turned the Carajás region, in the state of Pará, into a massive supply center of iron ore and other minerals destined almost entirely to foreign markets and involving a large area in north-eastern Brazil in terms of transportation and processing, both of which generating significant air pollution. In fact, every day the materials extracted from the Carajás mining complex travel along a 900 km railway, managed by Vale S.A. under a public concession contract, all the way to the São Luís harbor in the neighboring state of Maranhão, where they are then loaded onto cargo ships for export. In addition, about 3 % of the iron ore that travels along the so-called “Carajás corridor” reaches the São Luís harbor in processed form, thanks to exclusive sales agreements between Vale S.A. and companies based in Marabá, Açailândia, and Bacabeira that are specialized in converting raw iron ore into pig iron, the first step of the steel manufacturing cycle. In all three cities, the industrial area generates air pollution both through production and through transportation of material to and from the Carajás railroad.Açailândia’s industrial area was built right next to the Piquiá de Baixo neighborhood. Today, it consists of five steel plants that include 14 blast furnaces built at the beginning of the Greater Carajás Program in the late 1980s, plus three power plants and one cement plant that were added subsequently. This immense industrial complex sits in close proximity the local public school and private homes: the average distance is 400 m, with the closest homes only 50 m away and sits in close proximity to residential homes.At the onset of our study, we asked the local and state health board permission to consult community health records, backed by the International Federation of Human Rights (FIDH). However, we found the records to be incomplete and an unreliable source of quantifiable data . There aIn particular, according to an environmental evaluation mandated by the Court of Law of Acailândia in 2007, the “cohabitation” between the industrial complex and the local community is unsustainable for a number of reasons, including the impact of fine particulate matter and gases released by the blast furnaces, which run on a continuous cycle and without the use of chemical filters or gas incinerators .Besides pollution produced directly by the industrial complex, Piquiá residents incur in further exposure to toxic contaminants in connection to the transportation of raw and processed material along the stretches of the Carajás Railroad and federal highway BR 222 that run alongside their neighborhood. In fact, the railway carries over 300,000 tons of iron ore on a daily basis, while the local road connecting to the highway supports the everyday traffic of dozens of trucks that arrive to the processing plant carrying with charcoal and raw iron ore and leave loaded with either processed iron directed to the railroad or with waste material and dust destined to open air dumps that are scattered throughout the area Fig. .Fig. 1ScThe health risks associated with air pollution become exponentially dangerous also in light of the socio-economic conditions of the resident population. In fact, over half of the houses in the neighborhood (54 %) are made of wood, which offers limited protection from dust infiltrations and another 12 % are made of mixed materials , while brick and stone buildings amount to only 34 % of all homes .Moreover, regardless of the type of construction, all homes are small (60 square meters on average) and have limited ventilation, which causes the dust to be a persistent factor of daily life, outdoor and indoor. Another aggravating factor in terms of respiratory risks is length of exposure to air pollution: 51 % of Piquiá families have been living here for a period ranging from 10 to 40 years and 43 % for a period ranging from 6 to 10 years . FinallyA health assessment report, requested by the Office of Public Defense of the State of Maranhão  in June of 2011, found 41 % of analyzed subjects to be afflicted by respiratory problems and drew the conclusion that there is a significant correlation between respiratory illness and poor air quality in Piquiá de Baixo . AnotherThe study on which this preliminary report is based aimed to follow up on the above mentioned surveys by assessing the incidence of respiratory pathologies among Piquiá residents in connection to high levels of air pollution generated by the local iron-processing complex.Data collection consisted in recording the medical history of participant subjects through questionnaires, concentrating on cardiovascular and respiratory pathologies, and assessing respiratory functions through simple spirometry tests, using a MicroLab Carefusion spirometer with Spirometry PC MicroMedical software, according to the latest international guidelines for forced expiratory procedures performed by participant subjects meeting the latest international guidelines for spirometry testing .The study was based on a cross-sectional sample of the Piquiá de Baixo neighborhood population, targeting every household and every person aged 16 or older over a limited period of time .The study has been approved by the Ethical Committee of the IRCCS Foundation, National Cancer Institute of Milan, Italy. All subjects provided informed consent to the participation; the purpose of the study and the spirometry procedure were explained to all participants with the support of the local community action organization.The study was divided into two phases. In the first phase, a specialized technician of the IRCCS Foundation/National Cancer Institute of Milan, Italy, met with community organization activists to illustrate the methods of data collection and research objectives. Members of the organization then led the technician from home to home, acting as mediators between her role as investigator and the role of residents as research subjects and assisting in the completion of medical history questionnaires and the performance of spirometry tests.This first phase accounted for 100 % of questionnaires collected and 70 % of all spirometry tests performed. The remaining 30 % of tests was carried out in the second phase by a local professional nurse. Quality of the data was superimposable between the two assessors.1), and Tiffeneau index (FEV1/FVC) have been expressed as a percentage of the predicted normal values, taking Brazilian theoretical values as reference [1/FVC > 0.7 and FVC < 80 %) and obstructive alterations (simple spirometry tests with FEV1/FVC < 0.7 and FEV1% < 80 %) [Values of forced vital capacity (FVC), expiratory volume in the first second (FEVeference . Spirome < 80 %) . The DepThe sample is constituted of 220 subjects out of a target population of 669; exclusion from the study was due to: unavailability for 434 subjects (most of whom were men and mostly due to work reasons), refusal to take the simple spirometry test in the case of 11 subjects, and infective contraindications for four subjects.The average age was 31 ± 15 years and there was an overall prevalence of women (62 %).1 values at the limit of the normalcy range . Results were pathological in the case of 66 out of 220 subjects or 28 % of the sample, subdivided as follows: 65 % of abnormalities were symptomatic of a mild restrictive defect , while the other 35 % were compatible with a mild obstructive lung disorder . Expressed as an overall percentage, this means that we found out 19.5 % of restrictive and 10.5 % of obstructive abnormalities, respectively.Simple spirometry testing of the population sample yielded mean FVC and FEVCigarette smoke was the first behavioral risk factor we considered when analyzing the results: 20 % of subjects claimed to be an active smoker and 14 % an ex-smoker. Among current smokers, there were slightly more men than women (56 % vs. 44 %) and their mean age was higher than that of the entire population sample (man age: 41 ± 13 years). In terms of frequency, 66 % of smokers in the sample claimed to smoke less than ten cigarettes a day, 27 % between 11 and 20 cigarettes, and 7 % over 40 cigarettes a day.The second factor we weighed when analyzing spirometry test results was exposure to smoke from charcoal stoves as the source of cooking heat in the neighborhood. We found that in most homes the stove is kept on outdoor porches that are roofed but open on the sides, precisely to ensure ventilation.The characteristics of exposure to risk factors that could concur in spirometric abnormalities are reported in Table The spirometric testing of lung functions carried out on a sample population of 220 Piquia residents - a community in Brazil known to be exposed to high levels of air pollution produced by a local iron processing complex- yielded abnormal results in 28 % of the sample. We consider this to be an extremely significant percentage from a medical standpoint, both in terms of sample demographics and compared to results found in similar studies.In fact, our sample represented a cohort of young adults (mean age: 31 years old), an age group that generally reports very low rates of spirometric abnormalities, among which the percentage of smokers was comparable to the national average for Brazil .In comparative terms, the European Community Respiratory Health Survey (ECRHS) is a significant reference. The study was carried out in the early 1990s based on general population samples in the 20-44-year-old age group in Europe and several non-European countries. According to the study, the prevalence of diagnosed bronchial asthma ranged from 2 % in Estonia to 11.9 % in Australia . More reThe prevalence of spirometric abnormalities yielded by our study remains significantly high also when compared to USA national data focused on the idiopathic pulmonary fibrosis. In fact, among rare respiratory diseases, idiopathic pulmonary fibrosis is the most common associated with a restrictive spirometric footprint. According to Raghu et al. , cases oThe significance of spirometric abnormalities associated with disorders of a restrictive kind in the cohort of Piquià residents we analyzed (19.5 % of the sample) is especially difficult to explain, since to date there are no published epidemiological studies from Brazil focused on restrictive lung disorders. However, we have grounds to believe that it is strongly correlated with the situation of heavy air pollution caused by the industrial complex. In fact, the presence of fine particles in the air we breathe is associated with a significant drop in respiratory function; and the air quality in Piquiá de Baixo is compromised by the emissions of fourteen blast furnaces that run on continuous cycle without filtering, plus the general polluting effects of the overall production cycle revolving around the local industrial complex.3) in the concentration of PM10 corresponded to a significant drop in the respiratory function of test subjects, quantified as follows: a 44.6 ml decrease in FEV1 and a 59.0 ml decrease in FVC, both expressed as absolute value [As regards fine particle pollution a recent study entitled ESCAPE (European Study of Cohorts for Air Pollution Effects) found that every 10 microgram increment per square meter  is close to the one found among Maranhão adolescents, which is 12.7 % , and to We acknowledge the limitations of our study, beginning with the limited representativeness of the sample, given its small size. This was mainly due to the impossibility to collect sufficient data from adult male residents due to work-related reasons: as the demographic group with greater employment opportunities, in fact, most men were unavailable for programmed home visits and spirometry test sessions. In light of the fact that employment rates in the community are higher among men than women and that many residents work in the iron processing complex or in connection with it, exposure to polluting substances deriving from iron processing is potentially higher precisely among men; in other words the demographic group for which our study is poor in data. This means that the prevalence of spirometric abnormalities and therefore of respiratory problems in the neighborhood population could be even higher than recorded.We are also aware that our data does not support direct conclusions on a direct cause-effect relationship between pollution generated from Piquià’s iron-processing plant and the spirometric abnormalities recorded in the local population. In fact, there are various causes that could concur with the pulmonary problems we documented, like the presence of other sources of air pollution, namely fine particles issuing from the trucks that transit on the highway junction road carrying raw and processed material, and the socio-economic context of the local population, as proven by studies that correlate poverty to lower respiratory development .Except for this last potential causal factor, however, we note that both the pollutants produced by blast furnace emissions and those released by the transportation of raw and processed materials to and from the Piquià industrial complex are connected to the presence of steel companies in the area. In a logic of prevention, we thus think it is of fundamental importance to assess, address, and remove all causes of fine particle pollution in Piquia.Moreover, we would like to point out that our study relies on spirometric abnormalities to evaluate the effects of industrial pollution on pulmonary functions and does not consider the potential correlation between fine particle pollution in the area and higher than normal incidence values of cancer pathologies in general and lung cancer in particular among the local population. Unfortunately, we could not inquire into this cause-effect relationship in the population under analysis, due to lack of specific records in the local health system regarding the incidence of lung cancer. However, given that several studies correlate the annual PM average to the incidence of lung cancer , 28, thiIn closing, the clinical data here reported, the lack of inspections and epidemiological records on the part of the public health system, and the particular environmental characteristics of the Piquia area documented by several court-mandated reports and surveys, lead us to define the Piquià case as emblematic of how the lack of health and environmental policies targeting industrial production results in severe impact on the health conditions of populations that reside in close proximity to processing plants tied to the steel industry.This independent study suggests that air quality in Piquiá de Baixo is likely to have a relevant impact on the respiratory health of local residents. Aside from the significant rate of lung function abnormalities we have recorded, research on the health conditions of populations that reside next to industrial steel processing plants alone justifies the need for urgent action to protect Piquiá de Baixo residents from the extremely high levels of pollution they are exposed to. Along with an immediate emergency response to redress the health hazards that threaten men, women, and children in the area (such as collective relocation) we believe that further action should be taken a) to improve the standards of industrial production in the Piquia industrial area, to reduce the effects of fine particle pollution and b) to raise greater awareness in this region of the Maranhão state regarding the connection between air quality and the health conditions of local residents and steel workers, following the example of similar programs implemented elsewhere in Brazil and South America .


Monte Carlo (MC) simulation has been used to generate commissioning data for the beam modeling of treatment planning system (TPS). We have developed a method called radial projection (RP) for postprocessing of MC‐simulation‐generated data. We used the RP method to reduce the statistical uncertainty of the lateral profile of proton pencil beams with axial symmetry. The RP method takes advantage of the axial symmetry of dose distribution to use the mean value of multiple independent scores as the representative score. Using the mean as the representative value rather than any individual score results in substantial reduction in statistical uncertainty. Herein, we present the concept and step‐by‐step implementation of the RP method, as well as show the advantage of the RP method over conventional measurement methods for generating lateral profile. Lateral profiles generated by both methods were compared to demonstrate the uncertainty reduction qualitatively, and standard error comparison was performed to demonstrate the reduction quantitatively. The comparisons showed that statistical uncertainty was reduced substantially by the RP method. Using the RP method to postprocess MC data, the corresponding MC simulation time was reduced by a factor of 10 without quality reduction in the generated result from the MC data. We concluded that the RP method is an effective technique to increase MC simulation efficiency for generating lateral profiles for axially symmetric pencil beams. To characterize the proton lateral profile accurately, it is required to measure the broad tail down to 0.01% of the central dose.MC simulation is by nature a stochastic process. Its outcome inevitably comes with statistical uncertainty. The common practice to reduce the uncertainty is to use variance reduction techniques (VRT), process a large number of particle histories, or increase the scoring volume during simulation.22.AHadrontherapy,http://geant4.web.cern.ch/geant4/). The new module describes the geometries and material compositions of the proton scanning beam nozzle, according to the design configuration provided by the nozzle manufacturer 2 and fill the corresponding histogram, assuming the beam center is at .During MC simulation for every energy deposition at voxel  in any given layer, find the corresponding bin by radius The resultant histogram  divided by the corresponding bin mass shows the dose profile as a function of radius.Ideally for this axial geometry, ring tally would be the default choice to take advantage from symmetrical geometry for scoring lateral profile. GateAlthough the cylindrical‐like approach allows the lateral profiles to be obtained directly from MC simulation, it still requires some code development. Also the work to re‐bin data during MC simulation, as stated in steps (2) to (4) above, is an extra burden to computational resource. To avoid any new code development or the downgrade of the MC performance, we used a completely different approach. We take the dose output data from the MC simulation, which is in 3D‐grid format, radially projected all voxel scores according to the distance to the beam center, calculated the mean value of multiple independent scores with the same radius, and used the mean as representative value for the radius. This approach did not require any new code development, nor did it add extra burden to MC simulation. The method is called as radial projection method, and described it in the next section.2.BVoxelize the cuboid scoring volume using cuboid voxels.Align pencil beams to be perpendicular to the scoring volume surface, with the beam center pointing to the center voxel on the surface.Project all voxel scores to an axis based on the radial projection distance of the voxels.Calculate the mean of the scores with the same radial projection distance, and use the mean as the representative score for the voxels with the same radial projection distance.The radial projection (RP) method assumes a pencil beam with axial symmetry impacting perpendicularly on a plane detector. The workflow for the RP method is as follows.1/12=28.87%) at the radius of 5. Another nice feature of the RP method is the number of voxels with the same radial projection distance becomes larger as the radius increases. As shown in the right panel of Fig. Figure point average, while the mean from the scores within a radius bin is termed interval average. A point on the radius axis, called boundary (R0), is used to divide the radius axis into high‐dose region and low‐dose region. In this study, we applied the point average to the high‐dose regions (r < R0), and the interval average to the low‐dose regions (r ≥ R0). The mean score of radius interval S¯ to define the boundary and the width of radius intervals (Δs). Figure R0) is defined as the first radius point whose corresponding point average dose is either equal to or less than the value of threshold (T). In the high‐dose region (r ≤ R0) represented by the magenta circle lines, point average was performed to obtain the mean score. After the radius passes the boundary, interval average was performed. The width of any radius interval Δ is wide enough to contain enough radius points that the sum of point averages is either equal to or larger than the value of threshold (T). As shown in Fig. 1 represented by a cyan ring and the 2nd interval is Δ2 represented by a green ring.We introduced a parameter called 2.Ci is the individual score of the voxels that correspond to the given radius, and x¯ is the mean of all scores in the sample set.In this study, we use the relative standard error (RSE) to quantify the statistical uncertainty for the MC‐generated data. The RSE is defined as eq. 33.A2 was placed 42.5 cm upstream from the isocenter. The voxel size of the sensitive volume was 1 × 1 × 1 mm3, and 2 × 107 protons were used in the MC simulation. We defined the conventional method as scores in the direction out from the pencil beam center. Figure Figure 32.93%7.27%=4.53) in noise reduction than the point average in the high‐dose region.We applied the RSE analysis to the same dataset. Figure 3.B2 were placed 42.5 cm upstream from the isocenter). In the first run, 2 × 108 protons were used; in the second run, 2 × 107 protons were used: 10 times less than that in the first run. The conventional method was used to obtain profiles from the first run's output, and the RP method was used to obtain profiles from the second run's output. Figures Because the RP method can reduce statistical uncertainty, it was expected that the RP method would reduce the number of required histories, as well as the MC simulation time. We ran the MC simulation twice for the same condition  of square field from MC‐generated profiles with the measured OF. The MC calculations agreed reasonably well with the measurements in both comparisons. It should be pointed out that the good agreement demands more than just a data‐noise‐reduction technique, such as the RP method. It at least requires properly model spot scanning nozzle with accurate geometry and applicable physics process, as well as carefully perform measurement.4−4 can be easily generated with 108 proton histories, as long as the full width at half maximum of the lateral profiles is less than 15 mm. Other investigators have shown, which was confirmed by our experience, that lateral dose profiles with spot shapes to the 10−4 level are needed to model the proton pencil beam properly.The application of the RP method substantially reduced the statistical uncertainty of spot lateral profiles generated by MC simulation for an axial symmetric pencil beam. The RP method has several advantages over the conventional method (a) it can generate a lateral profile of superior quality with the same particle history as shown in Figs. Hadrontherapy comes with a validated implementation of a cuboid tally. It does not require any additional code development because the RP method takes the output directly from cuboid tallies.The RP method obtains mean values from the independent scores at the same radius position (point average) or within a small radius interval . Essentially, it works in a manner like constructing ring tallies from cuboid tallies. The signal‐to‐noise ratio of a ring tally is obviously higher than that of any single cuboid tally. Therefore, applying the RP method to a cuboid tally offers three additional benefits. First, the cuboid tally is much more flexible than a ring tally because it can score any kind of dose distribution regardless of whether it is symmetrical or nonsymmetrical. Second, the RP method dose not re‐bin dose data during the MC simulation as the proposed cylindrical‐like approach . It is a trial‐and‐error process to determine the optimal value of the threshold for a given lateral profile. In this study, the typical threshold value varies between 0.1% and 1.0%. With increasing value of threshold, the lateral profile becomes smoother in the low‐dose region. However, it results in less data points and might potentially introduce distortion if the threshold is too high.There is a limitation to the application of the RP method. The RP method assumes the dose distribution is axially symmetrical, and error would be introduced when the distribution were not exactly axially symmetrical. The proton pencil beam is usually highly unsymmetrical at the entrance of the spot scanning nozzle. Because of the interaction of the proton particles with nuclei or electrons present in the nozzle's components and air, it becomes more symmetrical gradually down the beam path. In our facility, the cross section of the proton pencil beam has an elliptical shape at the isocenter. The corresponding ratio of the major axis over the minor axis varies from 1.05 to 1.15 with an average of 1.09. However the elliptical shape dies away gradually once proton beam enters to water. We ran a preliminary MC simulation to quantify the decrease in the elliptical shape in water tank. The result shows the difference of major axis to minor axis is approximately reduced to its half whenever proton beam goes through 10 cm water. During the acceptance and commissioning, we have not observed lateral‐profile asymmetry in water tang measurement. Also because the commercial TPS  used in our facility cannot model how the spot ellipticity changes with gantry rotation, we have to treat the pencil beams with axially symmetry, whether or not the range shifter was inserted. The potential error introduced by assumption of this axial symmetry has been also evaluated during commissioning and patient‐specific quality assurance. No noticeable discrepancy has been found thus far.5Herein, we described the concept of the RP method and how it can be implemented, and showed how the results of MC simulation can be improved using the RP method. The RP method is an effective technique for increasing the efficiency of MC simulation in generating spot lateral profiles for axial pencil beams.No conflict of interest exists in relation to this article.


An error in one linac was detected in that the nominal gantry speed was incorrectly calibrated. This test provides a practical method to quality‐assure critical aspects of VMAT delivery including dose versus gantry angle and gantry speed control. The method can be performed with any detector that can acquire time‐resolved dosimetric information that can be synchronized with a measurement of gantry angle. The test fulfils several of the aims of the recent Netherlands Commission on Radiation Dosimetry (NCS) Report 24, which provides recommendations for comprehensive VMAT quality assurance.In VMAT treatment delivery the ability of the linear accelerator (linac) to accurately control dose versus gantry angle is critical to delivering the plan correctly. A new VMAT test delivery was developed to specifically test the dose versus gantry angle with the full range of allowed gantry speeds and dose rates. The gantry‐mounted IBA MatriXX with attached inclinometer was used in movie mode to measure the instantaneous relative dose versus gantry angle during the plan every 0.54 s. The results were compared to the expected relative dose at each gantry angle calculated from the plan. The same dataset was also used to compare the instantaneous gantry speeds throughout the delivery compared to the expected gantry speeds from the plan. Measurements performed across four linacs generally show agreement between measurement and plan to within 1.5% in the constant dose rate regions and dose rate modulation within 0.1 s of the plan. Instantaneous gantry speed was measured to be within PACS number(s): 87.55.Qr RapidArc is the Varian version of volumetric‐modulated arc therapy (VMAT) that was first proposed by Otto.4.8∘/s. During delivery, primary control is dictated by the gantry speed due to the large mass of the treatment head making this the most difficult component to modulate and control rapidly and accurately. When less than approximately 1.7 MU/degree is required the gantry will move at maximum speed, but the dose rate will be dropped below 600 MU/min. When greater MU/degree is to be delivered, the maximum dose rate will be applied and the gantry speed will slow down.For the Eclipse treatment planning system , VMAT plans are composed of up to 178 control points. At each control point the gantry angle, cumulative dose fraction, and position of each MLC leaf is specified. At the linac, control is separated into two systems. Firstly, the treatment console controls the dose versus gantry angle by varying the dose rate and gantry speed as required to deliver the plan. The MLC controller provides control of the MLC position versus gantry angle. The gantry angle therefore synchronises for the two control systems and is critical to VMAT delivery. The nominal dose rate is usually set to the maximum 600 MU/min and the maximum leaf speed to 2.5 cm/s. The maximum gantry speed is limited in the Eclipse TPS to Linear accelerator quality assurance for VMAT has usually been based upon the work of Ling et al,.Accurate delivery of VMAT requires that the dose versus gantry angle control system is functioning correctly. This relies on the precise control and interplay of the gantry rotation speed and the dose rate and requires comprehensive testing that can quantify the accuracy as a function of the gantry angle. Since the Ling paper was published in 2008, a number of other authors have published on linac QA tests for VMAT.The aim of this work is to develop an efficient new method for VMAT QA that isolates and directly measures the dose versus gantry angle control system in near real time. The test is performed with gantry and dose rate modulation to simulate the conditions for clinical plan delivery. The method can validate both dose and gantry speed as a function of gantry angle. The method can be performed with any detector that can acquire time‐resolved dosimetric information and can be synchronized with a measurement of gantry angle. This provides a comprehensive new set of tests for both commissioning and regular quality assurance testing of VMAT delivery. Additionally, the tests aim to fulfil several of the aims of the NCS Report 24, which provides recommendations for comprehensive VMAT quality assurance.20×20 cm2 jaw‐defined field at all control points. The plan was run using DICOM RT mode. The VMAT CAP plan was chosen because it utilizes extremes of allowed dose rate and gantry speeds and also incorporates zero dose sectors. The plan operates in the counterclockwise direction, but a version was also created to run in the clockwise direction. The modified plans incorporate the following features:−128∘ to 128° as presented in the graphs)Arc range: 128° to 232° gantry rotation and vice versa for clockwise rotation 5.0∘/sGantry speeds: 0.5°, 1.0°, and A Varian Trilogy and three 21iX linear accelerators  operating in the 6 MV photon mode were used for all irradiations. To perform measurements, a “VMAT” test plan was required where the MLC had been retracted to form an open field. This was required to provide a constant field size and shape for dose measurement throughout delivery, noting that the MLC performance is not considered in this study. The required test plan was created by modifying the Varian VMAT customer acceptance plan, RA CAP MIL 6X 600DR, using the MATLAB programming language and software . For this purpose the MATLAB program was simply used as a DICOM editor. Within the DICOM header of the plan the central MLC leaf positions were manually altered so that they were retracted beyond a 24.4×24.4 cm with detectors spaced at 7.62 mm interpolated down to 1 mm.The IBA MatriXX  is a 2D ion chamber array designed for IMRT patient‐specific QA fluence measurements. It can be operated in movie (cine) mode which allows real‐time dose measurements and can be fixed in a gantry mount so that it rotates with gantry rotation. The system comes with an inclinometer that can be attached to the gantry during measurements to measure gantry angle. When the inclinometer is employed and the device is operated in cine mode, each image is tagged with the average measured gantry angle measured during acquisition of that image. The MatriXX can measure a maximum field size of dmax for the 6 MV beam to maximize the signal. The inclinometer was attached to the collimator head and calibrated using a spirit level. Acquisition was in movie mode at 30 ms sample time and 18 samples per image which provided an image every 0.54 s. This equates to an image approximately every 2.5° of gantry rotation at maximum allowed gantry speed. These parameters were chosen to optimize the balance between maximising temporal resolution while minimizing image noise.Dose versus gantry angle was measured using the MatriXX in the gantry mount. The MatriXX detectors have 0.3 cm inherent buildup so 1.2 cm buildup was added to put the effective point of measurement of the detectors at approximately MatriXX response linearity with dose was verified over a range of 3 to 300 MU and compared to Farmer chamber readings using 600 MU/min dose rate. This was performed using the mean value from a region of interest (ROI) on each image as was used for all subsequent dose measurements in this study.MatriXX response constancy with dose rate was verified over linac nominal dose rates ranging from 100 to 600 MU/min and compared to Farmer chamber readings.dmax buildup cap. The modified VMAT CAP plan was delivered and real‐time ion chamber signals were recorded  following the technique of McCurdy and Greer.20×20 cm2 open field at 600 MU/min. The results were plotted as relative dose versus time and compared to the plan. Once MatriXX measurements had been performed, they were similarly plotted as a time series and compared to the ion chamber measurements. Synchronization between time series was achieved using the dose ramp‐up of the linac and the point where signal was first measured.The MatriXX was benchmarked for VMAT measurements against a 0.6 cc Farmer‐type ion chamber. The ion chamber was placed in‐air at isocenter with Validation measurements for the MatriXX4.6×4.6 cm2 region of interest at the central axis, which includes 36 ion chambers on a 6×6 cm grid. These values were normalized to averaged measurements from a jaw‐defined static gantry 20×20 cm2 open field at 600 MU/min. The normalized MatriXX measurements were plotted against gantry angle from the inclinometer readings and compared to the plan, which was calculated using the control points from the DICOM header. The short‐term reproducibility of the MatriXX was tested by repeating the counterclockwise measurement five successive times using a sample time of 0.72 s/image.MatriXX measurements of the modified VMAT CAP plan were acquired in conjunction with the inclinometer. This allowed referencing of the relative dose measurements to gantry angle and hence providing a direct measure of the cumulative dose versus gantry angle control system. The relative dose reading from each image was obtained using the average value from a Both the dose versus gantry angle control and gantry speed control tests require real‐time data acquisition in the form of movie mode with the MatriXX. As such, the sample time for each test is critical to provide the best balance between maximizing temporal resolution and minimizing noise. To determine the optimal sampling for both tests a series of acquisitions were performed see .±0.4∘ (manufacturer help screen). The MatriXX inclinometer can only be used when the MatriXX is sampling in movie (cine mode). When the inclinometer is being used with cine mode, the average measured angle is attached to each image. The cine sample time is set by the user and for these measurements was set to 0.54 s/image (so that the dose versus gantry angle data could be used) and subsequently resampled to 1.08 s/image using a simple moving average. Using the sample time and the average gantry angle for each image, the average gantry speed between images was calculated and plotted as a time series. This was compared to the planned gantry speeds calculated from the control points in the DICOM header assuming the maximum possible dose rate between each point. The MatriXX inclinometer was used to measure gantry speeds with this technique in Rowshanfarzad et al.,Information on the gantry speed control during the VMAT plan could also be extracted from the dose versus gantry angle MatriXX measurements. The MatriXX inclinometer was attached to the linac collimator using tape. The inclinometer was calibrated at gantry 0° and 90° using a spirit level and is rated to have accuracy of Before utilizing the MatriXX for measurements, its suitability as a detector for this study was validated. Firstly, the dose response linearity and dose rate response constancy were tested after being normalized to ion chamber measurements.In the regions of constant dose rate, the Farmer chamber measurements agreed with the plan to within 0.6%. At the dose gradients there is agreement between measurement and plan to within one sample (0.72 s).5.0∘/s) corresponds to agreement to within 0.5°. −102∘ ,−112∘ and 112°  in where the dose rate drops below the plan value before recovering to the correct value, was evident for all linacs on the majority of measurements, but with variation in magnitude. Short‐term reproducibility was determined with five successive measurements. The standard deviation between the average values in the constant dose regions was 0.18%. This is within the noise range for an individual measurement of 1.5% . The dis±0.93∘/s in the constant gantry speed sections for the 0.54 s/image sample time. When the gantry speed changes, the measurements are in agreement with the plan to within two sample times (1.08 s). The optimal sampling time for the dose versus gantry angle was found to be 0.54 s. For quality assurance measurements, a single measurement and hence a single sampling time is preferential. Therefore, this sample time was investigated for the gantry speed testing in this section, as well as averaging of the data to 1.08 s/image using a simple moving average. The purpose of this was to minimize the noise in the constant gantry speed regions and the result was agreement with the plan to within 0.4∘/s (except for a single outlying point at 0.63∘/s). This resampling is justified as it does not compromise on the ability of the test to detect errors at the gantry speed changes, as this sample rate is still sensitive enough to detect such changes within one sample time.1.0∘/s of the plan. linacs LT and LZ have three and two points, respectively, with greater than 1.0∘/s difference with the plan. The maximum difference is 1.85∘/s measured for a single point on LT. At the largest changes in gantry speed (from 1.0∘/s to 5.0∘/s and vice versa), 0.36∘/s (1 SD). The time to agreement at changes in gantry speed was consistent between measurements at about three samples (2.16 s). This discrepancy is most likely due to inaccuracies in the inclinometer due to inertial effects at changes in speed, as shown in Rowshanfarzad et al.Five successive measurements were taken of gantry speed control throughout the plan on a single linac with sample rate of 0.72 s/image to test short‐term reproducibility. The agreement between measurement and plan during the constant gantry speed regions was to within The nominal maximum gantry speed for Varian linacs is calibrated to one revolution per minute. It has been found that if the nominal speed is slower than this then regular beam holds occur in the 82% dose regions of the plan, as illustrated in The results of The results of 0.07∘/s across all gantry speed regions; however, when the nominal gantry speed was at 66 s/rev the average agreement in the 5.0∘/s region of the plan drops from within 0.01∘/s to within 0.10∘/s.0.5∘/s difference).The gantry speed control measurements of The proposed method provides the first direct measure of the cumulative dose versus gantry angle control system during VMAT delivery and fulfils the aims of NCS Report 24 section 2.5.2.4.From the commissioning measurements, the MatriXX is deemed suitable for the measurements required for this study. Other detectors may also be suitable as long as a real‐time dose signal can be synchronized with a measurement of gantry angle. This could include an ion chamber placed at isocenter with a time‐resolved electrometer that is synchronized with an inclinometer or other method of determining gantry angle. The appropriate sample time must be found to strike the balance between minimizing noise and maximizing temporal resolution. For the MatriXX the optimal sample time was found to be 0.54 s/image for the dose versus gantry angle measurement, which was resampled to 1.08 s/image for the gantry speed test. For the dose versus gantry angle measurement, the measurement was compared to the plan in two ways: firstly, in the regions of constant dose rate. Percentage difference between measurement and plan was used, while the ability of the linac to correctly change dose rate at the correct time was compared using time to agreement. Reproducibility results across the four linacs and short‐term reproducibility on a single linac indicate that the measurement should fall within 1.5% of the plan in the constant dose regions and within 1 sample time (0.54 s) when the linac is changing dose rate. For the latter, the results measured during the sample time optimization indicate that the four linacs were able to alter dose rate within 0.1 s of the plan.−102∘  and manifests as a dose rate drop that overshoots the plan. When this occurs, it is also evident on the linac console dose rate readout. At this point in the plan, the linac is required to increase gantry speed from 1.0∘/s to 5.0∘/s as well as reduce dose rate from 600 MU/min (100% of maximum) to 494 MU/min (82% of maximum). The speed at which dose rate can be changed is dependent on the servo period of 50 ms. Due to the mass of the treatment head, changing gantry speed is more difficult for the linac to achieve. As such the unexpected drop in dose rate at gantry −102∘  is attributed to the lag in gantry speed as it increased from 1.0∘/s to 5.0∘/s. To deliver the correct MU/deg to satisfy the plan the linac compensates by reducing dose rate by dropping pulses (beam holds) until the gantry is at correct speed. The results of −112∘ and 112° . At gantry −112∘ and 112° , the linac changes gantry speed from 0.5 to 1.0∘/s and the cause of the beam holds is explained above. Since the change in gantry speed is smaller, it is logical that the linac can achieve the new gantry speed faster and this would explain why the beam holds are shorter in duration and, hence, the unexpected drop in dose rate isn't as severe as at gantry −102∘ .There were two regular features of the dose versus gantry angle plots  where thThe dose versus gantry angle measurements detected an error in that one of the linacs had an incorrectly calibrated nominal gantry speed. The nominal linac gantry speed is 1 revolution per minute, but on LZ one revolution was taking 66 s. This error manifested as a series of beam holds in the 82% dose region. The gantry speed modulation is dependent on the nominal gantry speed calibration and, if calibrated incorrectly, the linac compensates, using beam holds to correctly deliver the plan. This compensation is designed to ensure that the plan is delivered correctly, but such beam holds could possibly result in a suboptimal plan delivery and there is an additional risk that a further drift in nominal gantry speed or additional fault will result in the gantry speed reaching the point where compensation cannot be performed with dose rate, resulting in an interlock and an uncompleted delivery. The standard VMAT test for dose rate and gantry speed control is Ling test 2. For Ling test 2, when nominal gantry speed was altered the variation in result was less than 0.5%. As such, Ling test 2 was not sensitive to this error. The departmental response to the detection of the gantry speed miscalibration was to include into routine QA a measure of the time taken for the gantry to perform a complete revolution using a stopwatch.0.4∘/s (1 SD) during the 5.0∘/s region. When averaged over the 5.0∘/s region of the plan, the gantry speed is found to be within 0.01∘/s of the plan for all linacs. These results are also consistent for LZ after the nominal gantry speed calibration, as indicated in 0.10∘/s of the plan, which is inconsistent with the other linacs.The results of In further work to this study it is intended to attempt to apply the methodology using EPID‐based data acquisition to improve the availability of the method. It is also intended as part of this second study to perform a comparison with Dynalog files. It is believed that this may provide a direct validation of Dynalog files. It is also planned to use the results of the EPID measurements to rewrite the plan control points so that when this plan is then re‐imported into the TPS, the clinical impact of the measured variations can determined using DVH analysis.A new test to directly measure the accuracy of dose versus gantry angle and gantry speed for VMAT quality assurance was developed and tested. The dose versus gantry angle linac control system for VMAT treatment delivery was measured directly using the IBA MatriXX. Comparison between the measured results and the plan showed good agreement. From the data, the gantry speed control throughout the VMAT treatment delivery was also measured, generally showing good agreement with the plan. The tests were also found to be sensitive to a miscalibration of nominal gantry speed that, if undetected, may have led to a suboptimal VMAT treatment delivery. The tests fulfil several of the aims of NCS Report 24 (2015) on comprehensive VMAT quality assurance.A big thank‐you to Dr Mahsheed Sabet for her help in teaching the MatriXX operation. Thanks also to Dennis Pomare for his insights into the linac operations for VMAT delivery.This work is licensed under a Creative Commons Attribution 4.0 International License.Supplementary MaterialClick here for additional data file.Supplementary MaterialClick here for additional data file.