Performance of gimbal-based dynamic tumor tracking for treating liver carcinoma.
BACKGROUND
Since the introduction of tumor tracking in radiotherapy, it is possible to ensure a precise irradiation of moving targets. To follow the tumor movement, most systems rely on the detection of implanted markers and correlation models between the internal and external patient movement. This study reports the clinical workflow and first results of the dynamic tumor tracking (DTT) performance for patients with liver carcinoma at the Vero SBRT system of the University Hospital Erlangen regarding the detection of the internal marker and the changes of the determined correlation models.


METHODS
So far 13 liver patients were treated with DTT. For each patient, two fiducial markers (FM), which are monitored with X-rays during treatment, were implanted in the vicinity of the tumor. All patients received a fraction dose of 4-6 Gy with 8 to 12 fractions. Treatment and patient data is evaluated by processing the acquired log-files of the DTT treatment. Based on this, the marker detection and the changes of the correlation model between the internal and external movement is investigated.


RESULTS
The median treatment time was 19:42 min. During treatment a median of 173 X-ray stereoscopic images were acquired. The marker detection was successful in 64.6% of the images. The FM detection is independent of the relative angle between the marker and the imager, but shows a dependency on the average intensity surrounding the FM position within the kV images. The number of correlation models needed during treatment increases in the presence of baseline shifts. The comparison of the correlation models shows large differences in the internal-external correlation between the different models acquired for one patient.


CONCLUSION
Thirteen liver patients were treated with DTT at the Vero SBRT system and the marker detection was analyzed. Furthermore, the importance of regularly monitoring the internal target motion could be shown, since the correlation between the internal and external motion changes considerably over the course of the treatment.
['Ziegler|Marc|M|', 'Brandt|Tobias|T|', 'Lettmaier|Sebastian|S|', 'Fietkau|Rainer|R|', 'Bert|Christoph|C|']
D000368:Aged D000369:Aged, 80 and over D006528:Carcinoma, Hepatocellular D005260:Female D057918:Fiducial Markers D005500:Follow-Up Studies D006801:Humans D007091:Image Processing, Computer-Assisted D008113:Liver Neoplasms D008297:Male D008875:Middle Aged D011379:Prognosis D011879:Radiotherapy Dosage D050397:Radiotherapy, Intensity-Modulated D014057:Tomography, X-Ray Computed
Tumor tracking - stereotactic body radiation therapy - liver cancer - real-time monitoring