Dosimetric comparison of four different external beam partial breast irradiation techniques: Three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, helical tomotherapy, and proton beam therapy

Background and purpose: As an alternative to whole breast irradiation in early breast cancer, a variety of accelerated partial breast irradiation (APBI) techniques have been investigated. The purpose of our study is to compare the dosimetry of four different external beam APBI (EB-APBI) plans: three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), helical tomotherapy (TOMO), and proton beam therapy (PBT). Methods and materials: Thirty patients were included in the study, and plans for four techniques were developed for each patient. A total dose of 30 Gy in 6 Gy fractions once daily was prescribed in all treatment plans. Results: In the analysis of the non-PTV breast volume that was delivered 50% of the prescribed dose (PD), PBT (mean: 16.5%) was superior to TOMO (mean: 22.8%), IMRT (mean: 33.3%), and 3D-CRT (mean: 40.9%) (p < 0.001). The average ipsilateral lung volume percentage receiving 20% of the PD was significantly lower in PBT (0.4%) and IMRT (2.3%) compared with 3D-CRT (6.0%) and TOMO (14.2%) (p < 0.001). The average heart volume percentage receiving 20% and 10% of the PD in left-sided breast cancer (N = 19) was significantly larger with TOMO (8.0%, 19.4%) compared to 3D-CRT (1.5%, 3.1%), IMRT (1.2%, 4.0%), and PBT (0%, 0%) (p < 0.001). Conclusions: All four EB-APBI techniques showed acceptable coverage of the PTV. However, effective non-PTV breast sparing was achieved at the cost of considerable dose exposure to the lung and heart in TOMO. (C) 2008 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 90 (2009) 66-73