Evaluation of 3D-CRT vs. VMAT for radiotherapy of whole breast with simultaneous integrated boost

BACKGROUND AND PURPOSE: This study evaluates volumetric modulated arc therapy (VMAT) as a potential alternative to three-dimensional conformal radiotherapy (3D-CRT) for whole-breast radiotherapy (RT) with simultaneous-integrated boost (SIB). Patient/material and methods: Ten left-sided breast cancer patients previously treated in our institution (whole breast with SIB) were selected. Clinical plans were generated using tangential field-in-field 3D-CRT technique. VMAT plans were retrospectively created. Dosimetric evaluation was performed according to our clinical guidelines. A robustness evaluation of the 3D-CRT and VMAT plans against simulated anatomical and setup uncertainties was also performed. Differences between techniques were analysed using a two-sided Wilcoxon signed-rank test with a significance level of 0.05. RESULTS: Both the 3D-CRT and VMAT plans fulfilled the clinical requirements for target volumes and organs at risk. VMAT plans showed a median increase in heart mean dose of 10.8%, compared to 3D-CRT (p < 0.05). Heart maximum dose was reduced by up to 56.7% with VMAT (p < 0.05), offering a clinically meaningful advantage. For the ipsilateral lung, no significant difference in mean dose was observed, V16Gy was significantly lower and V4Gy was significantly increased with VMAT. VMAT plans improved dose conformity to the boost planning target volume, (p < 0.05). Median monitor units (MU) values of 371 MU (359-466 MU) vs 927 MU (752-1018 MU) were obtained with 3D-CRT and VMAT. VMAT remained robust to simulated uncertainties for whole-breast but showed greater sensitivity in the boost volume. INTERPRETATION: VMAT was a feasible alternative to 3D-CRT for whole-breast RT with SIB, improving boost dose-conformity and reducing maximum heart dose. However, VMAT requires careful dosimetric evaluation and robustness assessment.