A protective effect of morning radiotherapy on acute skin toxicity in patients with breast cancer: A prospective cohort study

The focus of this prospective cohort study was to evaluate the risk factors of severe acute skin toxicity (grade ≥2) in 100 patients with breast cancer (BC) during radiotherapy (RT). The patients were evaluated weekly during RT and 3 months after treatment. The endpoint included the occurrence of skin toxicity grade ≥2, according to Radiation Therapy Oncology Group (RTOG). Survival analysis was conducted by univariate and multivariate Cox regression analysis. In the multivariate analysis, RT in the afternoon (0–3 pm) (hazard ratios [HR] = 1.566, P = .042) was significantly associated with the early occurrence of skin toxicity, indicating a potential effect of chronotherapy related to this adverse event. In the univariate and multivariate analysis, skin phototype moderate brown (HR = 1.586, P = .042; HR = 1.706, P = .022, respectively) and dark brown or black (HR = 4.517, P < .001; HR = 5.336, P < 0.001, respectively) was significantly associated with the skin toxicity. Tangential field separation >21 cm (HR = 2.550, P = .009, HR = 2.923, P = .003), in women that were submitted to conservative surgery indicates indirectly that large breast size was also significantly associated with skin toxicity. Women with large breasts and dark brown or black skin should be followed more carefully during RT, which should be undergone in the morning, especially when submitted to conventional RT techniques, common in developing countries.