Evaluation of a clinical dose accumulation algorithm using deformable gel dosimetry

Abstract

Deformable 3D dosimetry represents a robust method of verifying the accuracy of clinical deformable dose accumulation algorithms used to monitor interfraction anatomical changes during radiotherapy treatments. For this study, a deformable abdominal phantom was developed incorporating a deformable nPAG gel dosimeter for the dose verification of Adaptivo™, a commercial software program with a deformable dose accumulation algorithm. A comparison was made for three single fraction irradiations of gel dosimeters, each with a different deformation state. Additionally, a comparison was made for the cumulative dose over a three-fraction treatment of a single gel dosimeter with individual fraction deformations matching those of the single fraction measurements. The single fraction irradiations resulted in target contour dose volume histograms (DVH) created by Adaptivo™ that were in close agreement with those determined by gel dosimeter measurements for doses similar to and higher than the planned target dose, with two of the three cases matching to within 5%. Discrepancies are attributed to a deformed contour compression during analysis in the cases where the phantom was deformed. The three-fraction treatment resulted in very close agreement between the DVHs determined through the gel dosimeter measurements and Adaptivo™ calculations across the full range of doses, with an average absolute discrepancy of 2.0% and a maximum absolute discrepancy of 6.3%.