Volumetric-modulated arc therapy for left-sided breast cancer and all regional nodes improves target volumes coverage and reduces treatment time and doses to the heart and left coronary artery, compared with a field-in-field technique

Abstract

We compared two intensity-modulated radiotherapy techniques for left-sided breast treatment, involving lymph node irradiation including the internal mammary chain. Inverse planned arc-therapy (VMAT) was compared with a forward-planned multi-segment technique with a mono-isocenter (MONOISO). Ten files were planned per technique, delivering a 50-Gy dose to the breast and 46.95 Gy to nodes, within 25 fractions. Comparative endpoints were planning target volume (PTV) coverage, dose to surrounding structures, and treatment delivery time. PTV coverage, homogeneity and conformality were better for two arc VMAT plans; V95%(PTV-T) was 96% for VMAT vs 89.2% for MONOISO. Homogeneity index (HI)(PTV-T) was 0.1 and HI(PTV-N) was 0.1 for VMAT vs 0.6 and 0.5 for MONOISO. Treatment delivery time was reduced by a factor of two using VMAT relative to MONOISO (84 s vs 180 s). High doses to organs at risk were reduced (V30(left lung) = 14% using VMAT vs 24.4% with MONOISO; dose to 2% of the volume (D2%)(heart) = 26.1 Gy vs 32 Gy), especially to the left coronary artery (LCA) (D2%(LCA) = 34.4 Gy vs 40.3 Gy). However, VMAT delivered low doses to a larger volume, including contralateral organs (mean dose [Dmean](right lung) = 4 Gy and Dmean(right breast) = 3.2 Gy). These were better protected using MONOISO plans (Dmean(right lung) = 0.8 Gy and Dmean(right breast) = 0.4 Gy). VMAT improved PTV coverage and dose homogeneity, but clinical benefits remain unclear. Decreased dose exposure to the LCA may be clinically relevant. VMAT could be used for complex treatments that are difficult with conventional techniques. Patient age should be considered because of uncertainties concerning secondary malignancies.

Keywords: VMAT; breast cancer; field-in-field; left coronary artery.