A comparison of two clinical correlation models used for real-time XXXX tracking of semi-periodic motion: A focus on geometrical accuracy in lung and liver cancer @entity1 .

@entity5 @entity1 @entity2 @entity1493
PURPOSE: A head-to-head comparison of two clinical correlation models with a focus on geometrical accuracy for internal @entity5 motion estimation during real-time @entity5 tracking (RTTT). METHODS AND MATERIALS: Both the CyberKnife (CK) and the Vero systems perform RTTT with a correlation model that is able to describe hysteresis in the breathing motion. The CK dual-quadratic (DQ) model consists of two polynomial functions describing the trajectory of the @entity5 for inhale and exhale breathing motion, respectively. The Vero model is based on a two-dimensional (2D) function depending on position and speed of the external breathing signal to describe a closed-loop @entity5 trajectory. In this study, 20 s of internal motion data, using an 11 Hz (on average) full fluoroscopy (FF) sequence, was used for training of the CK and Vero models. Further, a subsampled set of 15 internal @entity5 positions (15p) equally spread over the different phases of the breathing motion was used for separate training of the CK DQ model. Also a linear model was trained using 15p and FF @entity5 motion data. Fifteen liver and @entity2 @entity1 , treated on the Vero system with RTTT, were retrospectively evaluated comparing the CK FF, CK 15p and Vero FF models using an in-house developed simulator. The distance between estimated target position and the @entity5 position localized by X-ray imaging was measured in the beams-eye view ( @entity1493 ) to calculate the 95th percentile @entity1493 modeling errors (ME(95, @entity1493 )). Additionally, the percentage of ME(95, @entity1493 ) smaller than 5 mm (P(5mm)) was determined for all correlation models. RESULTS: In general, no significant difference (p>0.05, paired t-test) was found between the CK FF and Vero models. Based on @entity1 -specific evaluation of the geometrical accuracy of the linear, CK DQ and Vero correlation models, no statistical necessity (p>0.05, two-way ANOVA) of including hysteresis in correlation models was proven, although during inhale breathing motion, the linear model resulted in a decreased P(5mm) with 5-6% compared to both the DQ CK and Vero models. CONCLUSION: Dual-quadratic CyberKnife and 2D Vero correlation models were interchangeable in terms of geometrical accuracy with the CK linear ME(95, @entity1493 )=4.1 mm, CK dual-quadratic ME(95, @entity1493 )=3.9 mm and Vero ME(95, @entity1493 )=3.7 mm, when modeled with FF sequence. CK DQ modeling based on 15p acquired in 20 s may lead to problems for internal motion estimation.
