SU-F-19A-01: APBI Brachytherapy Treatment Planning: The Impact of Heterogeneous Dose Calculations

Authors


Abstract

Purpose:

To quantify the difference in dose to PTV_EVAL and OARs (skin and rib) as calculated by (TG43) and heterogeneous calculations (CCC).

Methods:

25 patient plans (5 Contura and 20 SAVI) were selected for analysis. Clinical dose distributions were computed with a commercially available treatment planning algorithm (TG43-D_(w,w)) and then recomputed with a pre-clinical collapsed cone convolution algorithm (CCCD_(m,m)). PTV_EVAL coverage (V90%, V95%), and rib and skin maximum dose were compared via percent difference. Differences in dose to normal tissue (V150cc, V200cc of PTV_EVAL) were also compared. Changes in coverage and maximum dose to organs at risk are reported in percent change, (100*(TG43 − CCC) / TG43)), and changes in maximum dose to normal tissue are absolute change in cc (TG43 − CCC).

Results:

Mean differences in V90, V95, V150, and V200 for the SAVI cases were −0.2%, −0.4%, −0.03cc, and −0.14cc, respectively, with maximum differences of −0.78%, −1.7%, 1.28cc, and 1.01cc, respectively. Mean differences in the 0.1cc dose to the rib and skin were −1.4% and −0.22%, respectively, with maximum differences of −4.5% and 16%, respectively. Mean differences in V90, V95, V150, and V200 for the Contura cases were −1.2%, −2.1%, −1.8cc, and −0.59cc, respectively, with maximum differences of −2.0%, −3.16%, −2.9cc, and −0.76cc, respectively. Mean differences in the 0.1cc dose to the rib and skin were −2.6% and −3.9%, respectively, with maximum differences of −3.2% and −5.7%, respectively.

Conclusion:

The effects of translating clinical knowledge based on D_(w,w) to plans reported in D_(m,m) are minimal (2% or less) on average, but vary based on the type and placement of the device, source, and heterogeneity information.

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