With 14 proton therapy centers currently operating in the United States and an additional 28 up and running worldwide, studies on the efficacy of using proton beam therapy for cancer treatment are being more widely conducted now than ever before.
“Ten years ago, there were only three proton centers operating in the United States, so the number of patients who were being treated and actually could be included in clinical studies was fairly small,” says William Hartsell, M.D., radiation oncologist with Radiation Oncology Consultants, Ltd., and medical director of the CDH Proton Center in Chicago, Illinois.
“But if you look at the percentage of those patients who were enrolled in clinical trials, it was actually a higher percentage than you would see from the conventional radiation therapy population,” he says. “Today, the vast majority of patients receiving proton therapy are either participating in a clinical trial or in a prospective registry trial where we are evaluating their outcomes.”
CDH Proton Center is involved in a number of clinical trials. Among them:
Sponsored through the Abramson Cancer Center at University of Pennsylvania, this study will determine the feasibility of using proton therapy in recurrent malignancies — either at the original disease site or adjacent to it.
“In either case, it’s difficult to give conventional [photon] radiation therapy a second time to that area,” says Dr. Hartsell. “So far, there have been about 150 patients who have been treated in this study, and they’ve done surprisingly well and tolerated the treatment much better than I would have predicted.”
Tumor recurrences being studied include pelvic tumors, such as rectal cancers; abdominal cancers, such as pancreatic cancer; chest cancers, such as lung cancer; head and neck cancers; and brain tumors.
“People who have had one cancer in the mouth or throat are at very high risk for developing a second cancer, due to damage to normal tissues from things like cigarette smoke or even viral infections,” says Dr. Hartsell. “With recurrent brain tumors, patients tolerate treatment with protons and do well, at least as far out as the follow-up that we have, which is still relatively short — one or two years.” (Recurrent brain tumors are being studied with Northwestern University through a separate protocol.)
Shorter treatment protocols
Lung: Working with clinicians at the University of Florida Proton Therapy Institute, Dr. Hartsell and his associates are studying the risks and benefits of hypofractionated proton therapy — that is, giving a higher proton dose along with chemotherapy over a shorter period — to treat lung cancer. The treatment course has been shortened from seven and a half weeks to four weeks, with the goal of reducing the course of treatment to between two and a half weeks and three weeks.
Prostate: For men with low-risk (slow-growing tumor) prostate cancer, the standard treatment frequency with protons is once daily five days a week for about eight weeks. In this study, through the Proton Collaborative Group, participants are randomly assigned to either the standard treatment or a course of hypofractionated proton treatments: five treatments over a week and a half. Two out of every three men get the shorter treatment course. So far, 100 men are in the study.
“Thus far, there doesn’t seem to be any difference in how the men are doing,” says Dr. Hartsell. “We need longer follow-up to make sure that’s the case in the long run. But in the short run, they’re tolerating [the accelerated] treatment really well.”
The CDH Proton Center is also conducting studies on locally advanced breast cancer, and intermediate- and high-risk prostate cancers.
In the past, proton therapy has been criticized for its lack of clinical studies and data comparing its efficacy with that of other types of cancer treatments. Now that tide is shifting. “I think that criticism was valid only because there were not enough proton centers to do the studies,” says Dr. Hartsell. “Now there is a critical mass of proton centers to perform them.”