Novel validation of HDR brachy therapy dosimetry for cervical cancer using egs_brachy Monte Carlo simulations: a comparative analysis with Oncentra treatment planning system

Abstract

Purpose: This study aims to validate HDR brachytherapy dosimetry for cervical cancer patients utilizing the egs_brachy Monte Carlo (MC) simulation. Methods: Three cervical cancer patients treated with 192Ir HDR brachytherapy were included. Dose distributions were calculated by the Oncentra Brachy v4 treatment planning system (TPS) based on AAPM TG-43. The newly developed eb_gui, an egs_brachy graphical user interface for MC simulations, was applied in recalculating dose distributions for 12 fractions using digital imaging and communications in medicine-radiotherapy (DICOM-RT) anatomical information. Comparisons were made for clinical target volume (CTV), bladder, and rectum using dose–volume histograms (DVH) and clinically relevant plan quality indices. Results: TPS-calculated doses were greater than those obtained from MC simulations. For the CTV, the median percentage differences were 7.9% (Q1: 6.4%, Q3: 9.8%; range: 0.4%–10.4%) for D90. For the bladder, the median percentage differences were 0.7% (Q1: 0.4%, Q3: 2.3%; range: −9.4–5.4%) for D2cc. For the rectum, the median percentage differences were 3.6% (Q1: 2.8%, Q3: 5.6%; range: 0.9%–6.4%) for D2cc. Conclusion: CTV and critical organ doses calculated by the TPS were consistently greater than those obtained from MC simulations. This suggests that the TPS may overestimate dose distributions, especially in heterogeneous regions like the pelvis. These results emphasize the need for continued validation of TPS algorithms in HDR brachytherapy for cervical cancer.