Proton therapy for breast cancer treatment is “safe and effective.” That’s the conclusion of a new study released in the Journal of Clinical Oncology, which highlighted proton therapy’s ability to control cancer cells with much less toxicity in the heart and lungs as compared to conventional (x-ray) radiation therapy.
“In our prospective trial of women with locally advanced breast cancer who required treatment of the internal mammary nodes, proton beam radiation therapy was safe and effective,” says Shannon M. MacDonald, MD, of Massachusetts General Hospital in Boston, and colleagues.
Breast cancer tumors usually occur in the lobules and ducts of the breast, which are used in the production and delivery of breast milk. Breast cancer is the most common cancer among women aside from skin cancer. Men are also susceptible to breast cancer, although the disease is rare among males.
As with other cancers, the best possible outcomes for breast cancer treatment come through early breast cancer care. Proton therapy has unique attributes that reduce radiation exposure to normal, healthy organs3,4. This is especially important in left-sided, node positive breast cancer patients (those who need the internal mammary nodes irradiated), as the cancer is close to critical organs such as the heart and the lungs.
How Massachusetts General Hospital conducted the study
Researchers enrolled 70 prospective patients with nonmetastatic breast cancer who required radiation therapy to the chest wall and regional lymph nodes. The average age of enrollees was 45, with patients ranging from 24 to 70 years old. The vast majority (91%) of evaluable patients had left-side breast cancer, and all but four patients had stage II-III disease. Only one patient did not receive chemotherapy in conjunction with proton radiation therapy.
The study, which lasted from 2011 to 2016, specifically chose patients whose treatment would include irradiation of the internal mammary nodes (IMNs). This made them suboptimal candidates for conventional radiation therapy, since exposure to the IMNs would also increase radiation to the heart and lungs. According to the study’s authors, that has been associated with an increased risk of cardiac events.
The benefits of proton therapy, however, significantly reduce exposure to the heart and lungs. It’s an advanced form of radiation therapy that precisely targets a tumor using a single beam of high-energy protons to kill cancer cells. Unlike conventional photons, which have almost no mass and extend beyond a tumor through the body, protons are relatively heavy and will hit their target – then stop. This spares nearby healthy tissues and organs from receiving unnecessary radiation.
Summary of the study’s results
Proton therapy for breast cancer treatment received high marks from this study. Of the 69 evaluable patients, the 5-year cancer recurrence rate was just 1.5% and the 5-year overall survival rate was 91%. Those positive results go hand-in-hand with low rates of severe side effects. Study authors reported no patient developed grade 3 pneumonitis (inflammation of the lungs) or grade 4 or higher toxicity in the lungs. They also reported no significant changes in cardiac function or key cardiac biomarkers.
Dr. MacDonald and colleagues concluded that “Proton beam radiation therapy (RT) for breast cancer has low toxicity rates and similar rates of disease control compared with historical data of conventional RT.”
“Among mostly young women with left-sided breast cancer receiving regional nodal irradiation, proton therapy produces excellent target coverage with miniscule cardiac doses and low rates of lung toxicity,” Dr. Wilkinson says about the study’s conclusion. “When we treat breast cancer, those lymph nodes run very close to the heart. Proton therapy allows us to deliver the dose to the tumor site and spare the surrounding area – the heart, lung, chest wall, and even the esophagus.”
What’s next for proton therapy research?
The authors of the study from Massachusetts General Hospital say their findings open the door for more extensive studies in the future. “No early cardiac changes were observed,” they note, “Which paves the way for randomized studies to compare proton beam radiation therapy with standard radiation therapy.”
In fact, the results of the study bode well for a more comprehensive trial already underway to compare proton therapy with conventional x-ray therapy. The Radiotherapy Comparative Effectiveness (RADCOMP) Consortium Trial, which began in 2016 and will continue until at least 2022, is being conducted by the University of Pennsylvania, in conjunction with the Patient-Centered Outcomes Research Institute.
According to the U.S. National Library of Medicine, it is a pragmatic randomized clinical trial of patients with locally advanced breast cancer. More than 1,000 patients will be randomly assigned to receive either proton therapy or x-ray therapy. Each patient will have a 50-50 chance of getting into either treatment group. Both groups will be followed for at least 10 years after completing radiation therapy. The trial’s ultimate goal to is to study the patients’ quality of life outcome to help decide which is the best treatment option for future patients with breast cancer – proton therapy or x-ray therapy.
The Benefits of Proton Therapy for Breast Cancer Treatment
Proton therapy shows remarkable promise and advantages over conventional therapy in the treatment of breast cancer. It is a type of radiation that stops at a very specific point in the targeted tissue; conventional radiation continues beyond the tumor. In breast cancer, this means on average no radiation to the heart and on average 50% less radiation to the lung5 as compared with conventional radiation.
Proton therapy is extremely precise and therefore more effective at targeting cancerous cells without causing damage to surrounding breast tissue. It is not a substitute for a lumpectomy. Rather, it is used as an alternative to conventional radiation therapy. After surgery a breast cancer patient may receive 2-6 weeks of proton therapy.
- Phase II Study of Proton Beam Radiation Therapy for Patients with Breast Cancer Requiring Nodal Irradiation. Journal of Medical Oncology
- Pragmatic Randomized Trial of Proton vs. Photon Therapy for Patients with Non-Metastatic Breast Cancer: A Radiotherapy Comparative Effectiveness (RADCOMP) Consortium Trial. ClinicalTrials.gov
- MacDonald S, Specht M, Isakoff S, et al. Prospective pilot study of proton radiation therapy for invasive carcinoma of the breast following mastectomy in patients with unfavorable anatomy – first reported clinical experience. Int J Radiat Oncol. 2012;84(Suppl 3):S113-S114. Abstract 281
- Moon SH, Shin KH, Kim TH, et al. Dosimetric comparison of four different external beam partial breast irradiation techniques: three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, helical tomotherapy, and proton beam therapy. Radiother Oncol. 2009;90:66-73.
- Early Toxicity in Patients Treated with Postoperative Proton Therapy for Locally Advanced Breast Cancer. U.S. National Library of Medicine, National Institutes of Health