Partial breast irradiation delivered with proton beam: results of a phase II trial

A phase II trial sought to determine the safety and efficacy of proton beam irradiation to deliver partial breast radiotherapy after lumpectomy for early-stage breast cancer.

Eligible patients included women with invasive nonlobular carcinoma ≤ 3 cm. Surgical therapy included lumpectomy with negative margins and negative axillary lymph nodes on sampling. Postoperative proton radiotherapy to the surgical bed with an additional 1-cm margin was delivered by 40 Gy in 10 fractions over a 2-week course. Patients received systemic therapy as recommended after proton treatment. Patients had clinical evaluations every 6 months and annual mammograms.

Fifty patients were enrolled; median follow-up was 48 months. All patients completed the prescribed treatment. Acute toxicities were limited to mild radiation dermatitis. Late skin toxicities included 3 grade 1 telangiectasias. There were no posttreatment infections or ulcerations and no cases of fat necrosis, rib fractures, radiation pneumonitis, or cardiac events. Actuarial 5-year overall survival and disease-free survival rates were 96% and 92%, respectively. No local failures occurred. Ipsilateral breast cancer developed in 1 patient 5.5 years after treatment. Dose-volume histogram analysis showed near-complete elimination of dose to the contralateral breast, lung, and heart.

Proton partial breast radiotherapy appeared to be a feasible method of treatment and provided excellent disease control within the ipsilateral breast. Treatment-related toxicity was minimal and no technical limitations prevented treatment delivery. The incidence of posttreatment complications may be less than that reported when using more invasive techniques; comparative trials should be considered.