Proton Beam RT in Breast Cancer Provides Benefit, But More Research Required

Brandon Scalea Published: Wednesday, Dec 19, 2018

There are clear advantages to using proton beam radiation instead of standard radiation in certain patients with breast cancer, said Kimberly S. Corbin, MD; however, there is still work to be done before this practice becomes more widespread. As it is more precise, proton therapy would be an optimal approach, said Corbin, who is a radiation oncologist at the Mayo Clinic. Standard radiation can be particularly risky in select patients, she added.

Early-phase clinical trials are underway to get a better understanding of the role of this therapy in breast cancer treatment. One phase II trial (NCT00614172) is evaluating the safety and efficacy of proton therapy following lumpectomy in patients with early-stage breast cancer. For patients enrolled in the trial, proton radiotherapy will start 2 to 4 weeks following surgical excision. The treatment area will include the lumpectomy site with an additional margin, and daily proton therapy will be administered as an outpatient over a 2-week course. Primary endpoints will focus on survival and recurrence rates, while secondary endpoints will analyze toxicity and cosmetic results.

Radiation therapy is considered standard treatment for most women with early-stage breast cancer following lumpectomy. Postlumpectomy radiotherapy is known to reduce cancer recurrence in the breast and improve survival. However, in standard whole breast irradiation, portions of the chest wall, lung, and heart may also receive the radiation, which can lead to radiation-induced complications.

Radiation techniques with protons that limit the treatment area to the portion of the breast where the cancer presents can minimize, and even eliminate, radiation dose to these noncancerous areas, said Corbin. In an interview during the 2018 OncLive® State of the Science Summit™ on Breast Cancer, Corbin shed light on the use of proton radiation therapy in the space and which patients may benefit from this approach.

OncLive: How does proton therapy differ from standard radiation?

Corbin: Proton therapy is [comprised of] particles, [while] standard radiation is [comprised of] photons. By way of the physical properties of beam particles, they are heavier, and they have different dosimetric characteristics; [this enables us to] better spare tissue for radiation therapy. Usually when X-rays interact with tissue, they deposit energy along their path, and there is an entrance dose and an exit dose.

But for proton therapy, one of its dosimetric characteristics is that there is very little exit dose from radiation. Therefore, we can do a nice job of shaping the dose, while maximizing the ability to spare nontarget tissue from radiation.

What patients benefit the most from this therapy?

I primarily take care of patients with breast cancer, so that is the context with which I will answer the question, although this can be applied to many different kinds of malignancies. In terms of patients with breast cancer, a lot of patients have the need for comprehensive target volume coverage. Generally, this is for patients with the need for deep nodal detection or patients with a unique anatomy that makes standard radiation particularly high-risk. At the other end of the spectrum, proton therapy has a role for patients with early-stage breast cancer who are interested in a type of treatment called accelerated partial breast irradiation. That type of treatment is very focused and is used to target small volumes of tissue.”