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Proton Beam Radiotherapy for Breast Cancer

A proton therapy system.

A phase 2 trial reports that in patients with nonmetastatic breast cancer requiring postoperative radiation therapy, proton beam radiotherapy has low toxicity, with efficacy comparable to that of conventional radiotherapy.

A specialized type of external beam radiation, proton beam radiotherapy precisely targets a tumor with high doses of radiation to kill cancerous cells while minimizing damage to nearby tissue and critical organs such as the heart and lungs.

For this safety and efficacy study, completed at Massachusetts General Hospital in Boston and published this week in the Journal of Clinical Oncology, patients were eligible if they had nonmetastatic breast cancer requiring postoperative radiotherapy to the breast or chest wall and regional lymphatics and were considered suboptimal candidates for conventional radiotherapy. Seventy patients ranging in age from 24 to 70 completed proton beam radiotherapy between 2011 and 2016 and were followed for a median of 55 months. Of the 69 patients evaluable for analysis, 63 had left-sided breast cancer, 2 had bilateral breast cancer, and 5 had right-sided breast cancer; 94% had stage II to III cancer. All but one patient received systemic chemotherapy, and 50 patients underwent immediate breast reconstruction.

Patients received comprehensive radiation coverage, with a median dose of radiation to the chest wall and breast of 49.7 Grays (Gy), measured in terms of relative biological effectiveness, and 48.8 Gy to the internal mammary nodes. The study's primary end point was the incidence of grade 3 or higher radiation pneumonitis—an inflammation of the lung caused by radiation to the chest—or any grade 4 toxicity occurring within three months of treatment with radiotherapy. The study's secondary end points included five-year locoregional failure, five-year overall survival, and acute and late toxicities. Early cardiac changes were measured using strain echocardiography and cardiac biomarkers obtained both before and after the radiotherapy treatment.

Of the 62 surviving patients, 1.5% experienced locoregional failure over the course of five years, and five-year overall survival was 91%. One patient developed grade 2 radiation pneumonitis; none developed grade 3 radiation pneumonitis, nor did any patients experience any grade 4 toxicities. A third of patients (33%) required unplanned surgical reintervention over the course of five years. Radiotherapy did not cause significant changes in patients' echocardiography or cardiac biomarkers.

"Proton beam [radiation therapy] for breast cancer has low toxicity rates and similar rates of disease control compared with historical data of conventional [radiotherapy]," conclude the study authors, led by Rachel B. Jimenez, MD, Associate Program Director of the Harvard Radiation Oncology Residency Program. "No early cardiac changes were observed, which paves the way for randomized studies to compare proton beam [radiotherapy] with standard [radiotherapy]."

For More Information

Jimenez RB, Hickey S, DePauw N, et al (2019). Phase II study of proton beam radiation therapy for patients with breast cancer requiring regional nodal irradiation. J Clin Oncol. [Epub ahead of print] DOI:10.1200/JCO.18.02366

Image credit: Romina Cialdella. Licensed under CC BY-SA 4.0

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