Characterization of Dosimetric Differences in SAVI Treatment Plans Calculated with TG-43 Formalism and a Model-based Dose Calculation Algorithm.

Abstract: Purpose To comprehensively characterize dosimetric differences between calculations with a commercial model-based dose calculation algorithm (MBDCA) and the TG-43 formalism in application to accelerated partial breast irradiation (APBI) with the strut-adjusted volume implant (SAVI) applicator. Methods Dose for 100 patients treated with the SAVI applicator was re-calculated with an MBDCA for comparison to dose calculated via TG-43. For every pair of dose calculations, DVH metrics including V90%, V95%, V100%, V150% and V200% for the PTV_EVAL were compared. Features were defined for each case including 1) applicator size, 2) ratio between PTV_EVAL contour and 1 cm rind surrounding SAVI applicator, 3) ratio between dwell time in central catheter and total dwell time, and 4) mean CT number within the lumpectomy cavity. Wilcoxon rank sum tests were performed to test whether treatment plans could be stratified according to feature values into groups with statistically significant dosimetry differences between MBDCA and TG-43. Results For all DVH metrics, differences between TG-43 and MBDCA calculations were statistically significant (p Conclusions Investigated dose metrics for SAVI treatments were found to be systematically lower with MBDCA calculation in comparison to TG-43. Plans could be stratified according to several features by the magnitude of dosimetric differences between these calculations.