Hypofractionated radiotherapy with concomitant boost for breast cancer: a dose escalation study

Patients with breast cancer with pathological stage pT _1-2 and at least one risk factor for local recurrence such as N1 disease, lymphovascular invasion, extensive intraductal component, close margins, non-hormone sensitive disease, grading G3 were enrolled. Patients were treated with hypofractionated RT to whole breast with a dose of 40.05 Gy in 15 fractions. The dose was escalated to the tumour bed through a daily concomitant boost technique at three dose levels: 48 Gy (3.2 Gy/die), 50.25 Gy(3.35 Gy/die) and 52.5 Gy (3.5 Gy/die). Dose escalation to a higher step was carried out if all patients of the lower dose had completed the treatment without dose limiting toxicity (DLT). Skin toxicity, cosmetic evaluation and quality of life was evaluated at baseline, at treatment end and at 3 and 12 months after RT end.

Three patients for each dose level were enrolled. No DLT occurred. The maximum toxicity collected during RT was G2 skin toxicity in 3 (33.3%) patients, one for each dose level. No G2 toxicity at 3 and 12 months was collected. At median follow up of 21.8 months (range: 13.5 - 40.9 months), no G2 late toxicity was recorded.

The 3 week course of post-operative RT with dose escalation to the tumour bed to 52.5 Gy has been achieved without dose limiting toxicities and can be tested in Phase II trials.

In our study, we tested the highest dose level to the tumour bed ever reported in studies using accelerated hypofractionation with concomitant boost in high risk patients.