Optimizing Radiotherapy for Left Breast Cancer: A Dosimetric Evaluation of Hypofractionated vs. Conventional VMAT with DIBH

PURPOSE: This study aimed to determine whether the hypofractionated regimen offers dosimetric and radiobiological benefits compared to a conventional regimen delivered with deep inspiration breath-hold (DIBH) for left breast cancer patients following breast-conserving surgery using the VMAT technique. The primary objective was to assess whether the hypofractionated regimen provides equivalent target coverage and improved sparing of organs at risk (OARs). METHODS: Twenty-four patients with histologically confirmed left-sided breast cancer, aged between 42 and 68 years, were included and divided into two fractionation protocols: 12 received a conventional regimen (50 Gy in 25 fractions), and 12 received a hypofractionated regimen (40 Gy in 15 fractions). Dosimetric parameters including clinical target volume (CTV) coverage, homogeneity index (HI), conformity index (CI), number of monitor units (MUs), and dose to critical structures were compared between the two regimens. The biological impact of the different fractionation schemes was assessed by calculating the biological effective dose (BED) and the equivalent dose in 2 Gy fractions (EQD2). For statistical analysis, an independent-sample t-test was used (P < 0.05). RESULTS: Both treatment approaches provided excellent target coverage, with no significant differences observed in CI. The conventional VMAT plan demonstrated better dose homogeneity (HI = 0.165 ± 0.038) compared to the hypofractionated plan (HI = 0.304 ± 0.090; p < 0.001). The hypofractionated approach showed a tendency for increased sparing of organs at risk, notably a 28.7% reduction in mean heart dose (6.24 Gy vs. 8.91 Gy), a lower EQD₂ (4.27 Gy vs. 5.99 Gy), and a significantly reduced dose to the contralateral lung (5.62 Gy vs. 7.32 Gy; p = 0.029). For the contralateral breast, no statistically significant difference was observed (p > 0.05). CONCLUSION: Research indicates that hypofractionated VMAT with DIBH offers potential dosimetric advantages over the conventional regimen, most notably by reducing radiation exposure to the heart and contralateral lung.