Program Information
Monte Carlo Evaluation of the Dose Calculation Algorithm of TomoTherapy for Clinical Cases in Dynamic Jaws Mode
E Sterpin1, (1) ,Universite catholique de Louvain, Center of Molecular Imaging, Radiotherapy and Oncology, Brussels,
Presentations
SU-E-T-555 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: For the TomoTherapy™ system, longitudinal conformation can be improved by selecting a smaller field width but at the expense of longer treatment time. Recently, the TomoEdge™ feature has been released with the possibility to move dynamically the jaws at the edges of the target volume, improving longitudinal penumbra and enabling faster treatments. Such delivery scheme requires additional modeling of treatment delivery. Using a previously validated Monte Carlo model (TomoPen), we evaluated the accuracy of the implementation of TomoEdge in the new dose engine of TomoTherapy for 15 clinical cases.
Methods: TomoPen is based on PENELOPE. Particle tracking in the treatment head is performed almost instantaneously by 1) reading a particle from a phase-space file corresponding to the largest field and 2) correcting the weight of the particle depending on the actual jaw and MLC configurations using Monte Carlo pre-generated data. 15 clinical plans (5 head-and-neck, 5 lung and 5 prostate tumors) planned with TomoEdge and with the last release of the treatment planning system (VoLO™) were re-computed with TomoPen. The resulting dose-volume histograms were compared.
Results: Good agreement was achieved overall, with deviations for the target volumes typically within 2% (D₉₅), excepted for small lung tumors (17 cm³), where a maximum deviation of 4.4% was observed for D₉₅. However, such deviations were not observed for quality assurance measurements in homogeneous phantoms and were therefore attributed to dose calculation in patient geometry, not the modeling of TomoEdge. Such deviations for small lung tumors are also consistent with previously reported values for static field widths.
Conclusion: For the clinical cases considered in the present study, the introduction of TomoEdge did not impact significantly the accuracy of the computed dose distributions.
Funding Support, Disclosures, and Conflict of Interest: The author is partially supported by Accuray
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