Breast Cancer Patients Treated by Helical Tomotherapy, Intensity-modulated Radiotherapy, and Volumetric Arc Therapy: Comparison of Lung Doses

Introduction: We compared the dosimetry of three different radiotherapy (RT) techniques: helical tomotherapy (TOMO), intensity-modulated RT (IMRT), and volumetric modulated arc therapy (VMAT) in patients with breast cancer when the conventional technique was unworkable. Methods: We enrolled 16 patients that required treatment of residual internal mammary lymph node involvement (n = 9), with a planning target volume (PTV) close to the borders of the tangential fields of the conventional RT technique (n = 5), and with synchronous breast tumours requiring bilateral breast irradiation (n = 2). Planning computed tomography contours of these patients were retrieved, and virtual RT plans of all three techniques were developed for each patient for the purpose of dose comparison, with the objective of achieving optimal dose coverage to the PTV while minimising the lung dose and keeping the heart dose to the internationally recognised safe level. 42.56 Gy in 16 daily fractions was prescribed in all RT plans. Results: The PTV coverage and hot spot dose were comparable among all RT plans. The doses to organs at risk were converted to 2 Gy equivalent using an alpha,beta ratio of 3 for comparison. The mean lung dose (MLD), lung V5, and lung V20 were significantly lower using TOMO (MLD 10.2 Gy, V5: 30.3%, V20: 14.7%), compared with IMRT (MLD 11.9 Gy, p = 0.006; V5: 39.7%, p < 0.001; V20: 20.6%, p = 0.001) and VMAT (MLD 15.4 Gy, p < 0.001; V5: 52.3%, p < 0.001; V20: 27%, p < 0.001). The mean heart dose was significantly lower using IMRT (12.1 Gy) compared with TOMO (15.5 Gy, p = 0.017) and VMAT (14.9 Gy, p = 0.005). Conclusion: TOMO achieved lower lung doses, in terms of V5, V20 and MLD, compared with IMRT and VMAT.