ABSTRACT
Objective:To describe a prospective study of pre-operative tumor-bed boost performed at the 1.5 T MR-Linac in combination with adjuvant whole breast irradiation, and a first case, with an accentuation on clinical feasibility and safety.Methods:A phase II, single arm study recruiting early stage patients follows a paradigm that first boosts the tumor bed and then undergoes breast conservative surgery in 2 weeks, and last irradiates the whole breast in 6 weeks. The primary endpoint is ≥ grade 2 acute breast toxicity. A 43 years old patient affected by a breast carcinoma, not special type of the right-sided lateral quadrant, staged cT 2N 0M 0, was planned and treated. The dose, 8 Gy for one time, was calculated by Monaco on CT simulation images. Both the air electron stream effect (ESE) and the electron return effect (ERE) at the presence of 1.5 T magnetic field were evaluated. During the pre-treatment evaluation, we carried out adaptation-to-position adjustment. Results:The normal organ dosimetry is within toleration. The Dmax to the skin, the chin and the right upper arm was 8.44 Gy, 28.5 cGy and 17.8 cGy, respectively. There was no increased toxicity from ERE and ESE, and the treatment was well tolerated without > grade 1 acute toxicity. The patient received breast conservative surgery on day 7 without delayed wound healing.Conclusions:This is the first case successfully treated within a clinical trial by pre-operative tumor-bed boost under 1.5 T MR-Linac in our institution. More participants are needed to validate and optimize the paradigm.