Hypofractionated Online Adaptive Radiotherapy of Breast Cancer

Online Adaptive Radiotherapy (ART) is an evolution of image-guided radiotherapy that compresses the entire process of image acquisition, plan design, verification, and radiation delivery into approximately 10-30 minutes during which patients do not need to leave the treatment bed. Online ART features rapid image acquisition, automatic contouring and plan optimization supported by artificial intelligence. Body position deviation, breast soft tissue deformation, and organ movement in different treatment fractions can affect the accuracy of radiotherapy for breast cancer patients. Online adaptive radiotherapy is expected to have dosimetric advantages in terms of target coverage and organ-at-risk (OAR) dose reduction, thereby reducing treatment-related side effects while ensuring local tumor control. Moderate hypofractionation (40-43.5Gy/15-16f/3w) has been shown to achieve equivalent local tumor control and patient survival compared to traditional fractionationated regimens (50Gy/25f/5w), and may even reduce acute and late toxicities. Currently, moderate hypofractionationated radiotherapy has been a first-line recommendation for whole breast irradiation following breast cancer surgery. In addition, the FAST-Forward trial evaluated a shorter regimen, the ultrafractionated whole breast radiotherapy (26Gy/5f/1w) and found that local tumor control and normal tissue toxicity were comparable to the moderate hypofractionationated regimen. The Royal College of Radiologists (RCR) has endorsed 5-fraction ultrafractionationated radiotherapy as a standard option for postoperative breast cancer radiation treatment in 2020.