In order to understand the acute toxicities after whole-breast radiotherapy it is important to inform patients, guide treatment decisions, and target supportive care. Therefore in this research, reports of cohort of patients with breast cancer were accurately evaluated. Reports of 8,711 patients treated between 2012 and 2019 at 27 practices were analysed. Multivariable models identified characteristics associated with (1) breast pain, (2) bother from itching, stinging/burning, swelling, etc. within 7 days. After the evaluation, the results showed that moderate or severe breast pain was reported by 3,233 (37.1%): 1,282 (28.9%) of those receiving hypofractionation and 1,951 (45.7%) of those receiving conventional fractionation. Among patients receiving conventionally fractionated radiotherapy, younger age (P < .001), higher BMI (P = .003), Black (P < .001) or other race (P = .002), diabetes (P = .001), smoking status (P < .001), and larger breast volume (P < .001) predicted breast pain. Therefore it concludes that Intensifying supportive care may be appropriate for subgroups identified as being vulnerable to greater toxicity.