Effect of age and radiation dose on local control after breast conserving treatment: EORTC trial 22881-10882

Purpose: To determine whether the effect of an additional "boost" radiation after breast conservative therapy (BCT) on local control depends on age and evaluate the impact of a treatment policy with a threshold for age. Patients and methods: We used data from EORTC 22881-10882 trial, with median follow-up of 77.4 months. Patients receiving BCT and 50 Gy whole breast irradiation were randomized to no boost and 16 Gy boost (N = 5318). Results: In univariate analysis, a boost reduced local failure by a factor of 2 (P < 0.0001). Multivariate analysis showed local control increased with age (P = 0.0003). There was no evidence that the relative effect of a boost on local control depends on age (P = 0.97) However in younger patients the 5-year local failure was higher, therefore the absolute reduction was greater. If the threshold-age for boost treatment were set at 40 years, 8.4% of the study population would receive a boost, resulting in a 5-year local failure of 6.1% in the study population. Changing the threshold-age to 60 years, 67% of the study population would receive a boost and the 5-year local failure would be reduced to 4.4%. Conclusions: In younger patients a boost dose resulted in a greater absolute reduction of local failure. The relative risk reduction was however similar for all ages. Applying a treatment policy with a threshold-age of 60 would result in 0.6% increase in local failure in the total study population, while sparing the boost to 1/3 of the patients. (c) 2006 Elsevier Ireland Ltd. All rights reserved.