Impact of GBBS algorithm on post-mastectomy scar boost irradiation of breast using catheter flap

Introduction
Post-mastectomy radiation therapy significantly reduces locoregional recurrence rates, which can be achieved with external beam radiotherapy delivered to chest wall, followed by scar irradiation either by electron or high-dose-rate (HDR) mould brachytherapy. The present study evaluates dosimetric advantage of Acuros® BV, a TG-186 MBDCA, over TG-43 formalism using 192Ir source for HDR brachytherapy in chest wall scar boost using catheter flap.

Material and methods
A total of 25 patients, free of cardiac and pulmonary co-morbidities, who met the inclusion criteria were involved in the study. Catheter flap made of silicon with 20 channels was used to deliver a total dose of 7.5 Gy/3 fx by HDR surface mould brachytherapy to delineated scar volume. Plan was optimized with iterative method to obtain desired results with TG-43 formalism, followed by Acuros® BV (GBBS algorithm) without altering dwell positions or time. The two algorithm plans were analyzed qualitatively and quantitatively with dose-volume histograms.

Results
The mean D98% CTV-HDR_evl coverage decreased by 1.16% compared to TG-43, and near-maximum dose decreased by 8.18% (p = 0.000), mean Dmax dose to CTV-HDR_evl, and mean Dmean dose was lesser by 6.25% (p = 0.000) and 10.82% (p = 0.000), respectively, compared to TG-43. Heart D2% showed significant results, whereas Dmedian (cGy) revealed very significant difference. A 5 mm thick skin contour showed statistically significant results (p = 0.000) for V150% and V200%.

Conclusions
The presented data showed how Acuros® BV, algorithm-based calculation in scar boost irradiation of breast, accounting for a mass density of the medium and scatter condition, considered actual dose prediction in a medium.