Dose-volume histogram-based comparison of conventional and hypofractionated radiotherapy: lifetime attributable risk estimation in Indian breast carcinoma patients.

Aim: This study investigates secondary cancer risks in the contralateral breast (CB) and ipsilateral lung (IL) in postmastectomy radiotherapy (PMRT) patients treated with forward-planned intensity-modulated radiation therapy (IMRT). It is the first analysis of Dose-Volume Histogram (DVH)-based secondary cancer risks for patients undergoing forward-planned IMRT for PMRT. The objective is to compare cancer risks between conventional fractionated (CF) IMRT and hypofractionated (HF) IMRT. A retrospective analysis was conducted on 20 patients (aged 37-69 years) treated with 6 MV forward-planned IMRT. Treatment plans included CF IMRT (50 Gy in 25 fractions) and HF IMRT (42.56 Gy in 16 fractions). Organ equivalent doses (OED), excess absolute risk (EAR), lifetime attributable risk (LAR), and Relative Risk (RR) were calculated for CB and IL using Schneider non-linear mechanistic model & differential DVH. HF IMRT demonstrated a significant reduction in IL secondary cancer risk compared to CF IMRT (P = 0.0001), with LAR values decreasing from 54.9%-75.5% (CF) to 48.3%-66.5% (HF). The RR for IL cancer induction also declined from 10.16-13.6 (CF) to 9.06-12.1 (HF). In contrast, CB cancer risks exhibited minimal change, with LAR values slightly reducing from 1.08%-6.9% (CF) to 0.96%-6.1% (HF) (P = 0.52). The RR for CB remained relatively stable at 1.10-1.55 (CF) and 1.09-1.48 (HF). HF IMRT is more effective in reducing IL secondary cancer risk compared to CF IMRT, presenting it as a safer PMRT option. However, CB cancer risks remained largely unchanged, suggesting the need for further dose optimization research.