INTRODUCTION
RDS, breast cancer
BREAST CANCER
The use of accelerated partial breast irradiation (APBI) of 26 Gy in 5‐fraction daily treatments for patients with node‐negative early‐stage breast cancer, in contrast to whole breast radiotherapy of 40.05  or 42.56 Gy in 15 or 16 fractions in 3 weeks or longer, was recently introduced as the phase III randomized Fast‐Forward clinical trial for breast cancer patients.We have recently installed a single energy gantry‐mounted linear accelerator, the Varian Halcyon ring delivery system (RDS, V2.0), for image‐guided radiation therapy treatments (Varian Medical Systems, Palo Alto, California, USA). Halcyon RDS is equipped with 6MV‐FFF beam (mean energy = 1.3 MeV and depth of maximal dose = 1.3 cm) and is capable of rotating the gantry at a speed of 4 rotations per minute.With these advantages of Halcyon RDS in mind, Cozzi et al.