Impact of dose calculation algorithms on left-handed chest wall radiotherapy: A Monte Carlo and AAA dosimetric analysis

Abstract This study compares the dosimetric outcomes of the anisotropic analytical algorithm (AAA) and Monte Carlo (MC) algorithm in radiotherapy for left-sided breast cancer patients treated with half-beam volumetric-modulated arc therapy (HVMAT) postmastectomy. Twenty patients with supraclavicular node involvement were planned using HVMAT to deliver 42.56 Gy in 16 fractions with 6 flattening filter-free photon beams. Treatment plans were generated using the AAA (Eclipse treatment planning system [TPS] v17.0.1) and MC (Monaco TPS v6.1.2.0) algorithms. Dosimetric parameters were evaluated for the planning target volume (PTV) and organs at risk (OARs), including the heart, left anterior descending (LAD) artery, lungs, thyroid, and contralateral breast. The MC algorithm produced significantly higher D 95% , D 98% , and D max values for the PTV compared to AAA, indicating better target coverage. Although V107% values were similar between algorithms, MC plans achieved a superior conformity index, homogeneity index, and gradient index. In addition, MC-based plans resulted in significantly reduced radiation doses to the heart, LAD, ipsilateral lung, contralateral lung, total lung, skin, and thyroid. No significant differences were found in doses to the esophagus, spine, contralateral breast, or left femoral head. However, MC plans required a higher number of monitor units. In conclusion, while AAA remains a clinically convenient option, the MC algorithm offers superior dosimetric precision in anatomically complex chest wall regions. MC-based planning enhances dose uniformity and OAR sparing, suggesting its potential as a more effective and safer approach for left-sided breast cancer radiotherapy.