A large trial of people with earlier stages of prostate cancer compared two types of external radiation treatments head-to-head—proton beam therapy and intensity-modulated radiation therapy, or IMRT—and found that both helped control tumors while recording no differences in the patient’s quality of life.
The randomized study’s results were presented as a late-breaking feature at the annual meeting of the American Society for Radiation Oncology, known as ASTRO, being held in Washington D.C.
The 450 participants in the trial—with early- to intermediate-stage disease that hasn’t yet spread to the rest of the body—represent about 70% of the new prostate cancer cases diagnosed in the U.S. each year, and total more than 200,000 people annually. At those localized stages, multiple treatment options are available, but maintaining quality of life is a priority as many patients are expected to survive for several years after therapy.
IMRT, for example, relies on delivering X-ray radiation strong enough to help kill tumors, but the approach allows oncologists to shape and vary the power of the dose to limit its effects on nearby healthy tissue.
Proton beam therapy, meanwhile, utilizes charged particles that stop passing through the body once they’ve reached their target, and aim to cause irreparable breaks in the DNA of cancer cells. Its use has been slowly rising in clinical practice in recent years, but the approach is still substantially more expensive and requires specialized facilities.
“We tested two contemporary, advanced forms of external beam radiation for a very common cancer, and we demonstrated that both are very safe, effective treatments that give patients excellent outcomes in terms of quality of life and cancer control,” the trial’s principal investigator, Jason Efstathiou, vice chair of faculty and academic affairs in the department of radiation oncology at Massachusetts General Hospital, said in a statement.
Over a median follow-up period of more than five years, patients were asked to complete repeated questionnaires logging bowel, urinary and sexual function after receiving one of the two radiation therapies.
The researchers said that no major differences were seen between either approach at any point in the trial, with “only small, clinically nonmeaningful declines from baseline levels”—such as a not-statistically significant 2% drop in average bowel function scores within each arm of the study.
Rates of progression-free survival were also similar at five years, with 93.7% for IMRT and 93.4% with proton beam therapy. The median age of the study’s participants was 68 years old.
“We can use either of these tools with comparably excellent outcomes,” said Efstathiou, who also serves as a professor of radiation oncology at Harvard Medical School. “There have been so many advances in the delivery of contemporary radiation—such as the incorporation of scanned and modulated beams and in-room imaging—that I think the potential gaps between these technologies have narrowed over time.”
There were also no significant differences seen in certain, prespecified categories of patients, such as whether or not a rectal spacer was used during radiation delivery, or whether they were older or younger than 65.
“There may be subgroups that benefit from one technology over another, and we’re actively continuing analyses of that,” said Efstathiou, who noted one of the study’s limitations as its focused on localized versus more advanced prostate cancers.
“Providing the best evidence-based care calls for rigorously testing the tools we use for that care. We commonly use randomized controlled trials to evaluate new drugs, for example, but not necessarily for new technologies,” he said. “I hope that our work shows that randomized, controlled trials are critical in technology assessment.”
“As a practicing radiation oncologist who treats men with prostate cancer, and has access to both proton beam and IMRT, I think this is a a tremendous study,” Sameer Keole, the incoming president of ASTRO and an assistant professor of radiation oncology at the Mayo Clinic, said at the meeting. “This is a modern-era study, and I think it shows us that we have two great options.”
“To me, the take-home point is that the [tumor] control rates are phenomenal and the complication rates are very low,” Keole added. “I think men can go seek the definitive treatment when it's appropriate, and know that external-beam radiation therapy—whether it's proton therapy or IMRT—is an excellent treatment option.”