Impact of chemotherapy dose-density on radiotherapy dose-intensity after breast conserving surgery.

Purpose: To evaluate if chemotherapy (CT) dose-intensification jeopardizes radiotherapy (RT) dose-intensity (DI). Patients and methods: From 1992 to 1997, 247 stage I-II breast cancer patients, treated with conserving surgery, were treated at the National Cancer Institute of Genoa in a randomized study comparing the same CEF regimen delivered every two weeks (CEF14) or three weeks (CEF21). RT was applied to the residual breast at a total dose of 50 Gy in five weeks. Allowance was made for treatment at 2.3 Gy per fraction in order to compensate for gaps (hypofractionation). Radiotherapy DI was expressed as the average total dose received each week, i.e., 'weekly dose-rate' (WDR). The effect of various tumour, treatment and patient-related factors on the endpoint (a delivered WDR of RT < 9.5 Gy) was investigated by univariate analysis. Factors found to have P-value less than or equal to 0.20 were entered in multivariate analysis. Results: All but three patients (244 of 247, 98.8%) received a cumulative total dose of RT within +/- 10% of that planned. Moreover, most of them (197 of 247, 79.8%) received an average WDR of greater than or equal to9.5 Gy/wk. With univariate analysis the probability of WDR < 9.5 Gy/wk significantly correlated with age, menopausal status, concomitant administration of RT and CT, and white blood cell toxicity. Moreover, a positive effect on WDR was found in patients treated at 2.3 Gy per fraction. The type of treatment (CEF14 vs. CEF21) did not affect the probability of WDR < 9.5 Gy/wk. With multivariate analysis, age (less than or equal to 55 vs. > 55 years, RR = 3.99, 95% CI: 1.89-8.42, P = 0.0003), RT fractionation (conventional vs. hypofractionation, RR = 0.32, 95% CI: 0.15-0.68, P = 0.017) and WBC toxicity (none vs. some, RR = 1.54, 95% CI: 1.06-2.22, P = 0.027) were independent predictors of WDR < 9.5 Gy. Regarding the CT-RT overlap, patients receiving more than two cycles of chemotherapy during radiotherapy had an increased risk of RT delay compared to other patients (RR = 3.74, 95% CI: 1.44-9.48, P = 0.0063). Conclusions: There is no evidence of a direct effect of CT dose-density on dose-intensity of RT. However, the concomitant use of CT and RT reduces the possibility of giving a full dose-intensity of RT.