Dosimetric Comparison of Particle Radiotherapy and Photon VMAT for Left-Sided Breast Cancer Post Breast-Conserving Surgery.

IntroductionCarbon ion radiotherapy shows potential for left-sided breast cancer, yet comparative dosimetric data remains limited. This study retrospectively compared the dosimetric characteristics of proton and carbon ion radiotherapies with conformal radiation therapy, intensity-modulated radiation therapy, and volumetric-modulated arc therapy (VMAT) for left-sided breast cancer patients after breast-conserving surgery, exploring heavy ion radiotherapy's potential as promising treatment.Materials and MethodsEighteen patients staged I/II were enrolled. Treatment plans were created using three treatment planning systems: Oncentra® for photon beams, RayStation® for proton, and CiPlan® for carbon ion. The primary objective was to deliver 100% of prescribed dose to 95% of the PTV and PTVtb volumes. Dosimetric parameters for the target and organs at risk (OARs), including conformity indices (CI) and homogeneity indices (HI), were compared using the Friedman M-test.ResultsAll treatment methods met the target coverage planning objective and the prescribed dose, without any statistically significant differences. Carbon ion therapy (CI: 0.69±0) exhibited improved conformality compared with IMRT (CI: 0.43±0.01, P < 0.01) and CRT (CI: 0.3±0.01, P < 0.01), without significant advantage over VMAT. The carbon ion method (HI: 1.08±0.00) didn't exhibit any significant improvement in homogeneity compared with other treatments. Carbon ion therapy generally reduced the Dmean or V5 of OARs, particularly providing superior protection than VMAT for organs including contralateral breast (Dmean: 0.19±0.06 Gy (RBE)), heart (Dmean: 1.23±0.35 Gy (RBE), V5: 3.92±4.55 %), and contralateral lung (V5: 0.01±0.00 %). The carbon method also demonstrated significant dosimetric superiority over proton in V5 of ipsilateral lung (Carbon: 18.89±7.79 % vs proton: 26.29±9.02%, P = 0.011).ConclusionThe study suggested heavy ion therapies could provide dosimetric advantages over photon and proton therapies in planning conformity and OAR protection. These advantages could bring potential clinical benefits, reduced side effects, and improved therapeutic outcomes.