Volumetric Modulated Arc Therapy Versus Three-Dimensional Conformal Radiotherapy for Breast Cancer Patients Treated with Regional Nodal Irradiation

Abstract

Locally advanced breast cancer is often treated with adjuvant radiotherapy to the chest wall or breast and the regional nodes following surgery. Intensity-modulated radiotherapy (IMRT) can improve target coverage and spare organ at risk, but the efficacy and safety of IMRT for locally advanced breast cancer have not been clarified. We aimed to compare the dosimetric parameters and clinical outcomes between 3D-CRT and volumetric modulated arc therapy (VMAT) for breast cancer. The hypothesis is that VMAT has better target coverage without increasing toxicities. Breast cancer patients who received adjuvant radiotherapy with regional nodes irradiation between July 2016 and December 2019 were included. Patients with a right-sided disease were treated with three-dimensional conformal radiotherapy (3D-CRT), whereas patients with a left-sided disease were treated with VMAT to reduce heart dose. Patients who received bilateral radiotherapy were excluded. Radiotherapy was delivered to the chest wall or breast, and supraclavicular region with or without internal mammary nodes. A dose of 50 Gy in 25 fractions was prescribed to the reference point for 3D-CRT, and to cover 75% of the PTV for VMAT. Single full or two partial arcs with 6MV were used for VMAT. Clinical outcome and dosimetric data were collected retrospectively from medical records. Toxicities were assessed by CTCAE ver.4.0. A total of 74 consecutive patients were included in this study. Thirty-five left-sided breast cancer patients received VMAT, and 39 right-sided breast cancer patients received 3D-CRT. The median follow-up was 591 days. The median age was 50 years. Grade 2 or higher acute dermatitis were observed in 10 patients (29%) with VMAT versus 17 patients (44%) with 3D-CRT (P = 0.18). Grade 3 acute dermatitis occurred in one patient in the 3D-CRT group. Grade 2 radiation pneumonitis occurred in one patient in each group (P = 1.0). Acute radiation esophagitis occurred in 25 patients only in the VMAT group. CTV coverage (CTV V47.5Gy, D95%, D75%) was significantly better for VMAT (86%, 42 Gy, 49 Gy) compared to 3D-CRT (72%, 29 Gy, 46 Gy) (all P < 0.01). Total lung V20 Gy was lower for VMAT versus 3D-CRT (11Gy versus 13 Gy, P < 0.01), whereas total lung V5 Gy and mean dose were higher for VMAT (34 Gy and 7.8 Gy) compared to 3D-CRT (22 Gy and 6.9 Gy) (P < 0.01, 0.01). Because of the laterality, the dose to the heart and esophagus was higher in the VMAT group (P < 0.01, 0.01). Five patients experienced recurrence (two distant metastases in the VMAT group and two distant and one local and distant metastases in the 3D-CRT group). VMAT for breast radiotherapy with regional nodal irradiation had better target coverage and lower lung V20 Gy at the expense of a small increase in the lung mean dose and V5 Gy. VMAT can be safely administered with similar toxicity to 3D-CRT.