CHICAGO – Some patients will go to great lengths – literally – to receive proton beam radiotherapy for prostate cancer, but there is still little evidence to date to support its use over intensity-modulated radiotherapy in this population, investigators noted at the annual meeting of the American Society of Clinical Oncology.
Although some patients traveled cross-country to be treated at one of six proton beam therapy (PBT) centers, the only significant difference in adverse event outcomes between the costlier proton therapy and the more widely available intensity-modulated radiotherapy (IMRT) was lower 6-month genitourinary toxicity with PBT (5.9% vs. 9.5%; odds ratio, 0.60; P = .03), reported Dr. James B. Yu, a radiation oncologist at Yale University in New Haven, Conn., and colleagues.
"We found that the rate of complications was transiently better for proton therapy, but at 1 year there was no difference between that and IMRT," Dr. Yu said in an interview. He reported the 12-month rate of genitourinary complications as statistically similar, at 18.8% with PBT and 17.5% with IMRT.
There were no significant differences between the two types of therapy in gastrointestinal or other toxicities at either 6 or 12 months.
The Yale investigators obtained data on all Medicare claims in 2008 and 2009 from the Medicare Chronic Condition Warehouse database. Looking for both patterns of care and clinical outcomes, they identified a total of 27,647 men (aged 66-94 years) who received either PBT or IMRT.
Patients All Over the Map
They also found that the 421 men (1.5% of the total cohort) who underwent PBT came from all over the U.S. map, and that more of them sought treatment at centers 75 miles or farther from where they lived (5.7%, compared with 4.9% treated at centers within 75 miles of home).
Curiously, some patients traveled across the entire country even when there was a proton facility in their backyard. For example, several patients flew from California, where there is a proton therapy center at Loma Linda University, to the University of Florida in Jacksonville, whereas others traveled from Boston, where Massachusetts General Hospital has a proton beam center, to California.
"We’re not really sure why they did this, but our hypothesis is that there are two tiers of health care in this country, with some folks who can and are willing to fly across the country for treatment, and others who go down the street for their care," Dr. Yu said.
Patients treated with PBT tended to be younger and healthier, and have a higher socioeconomic status, the investigators found.
Findings in Line With Other Studies
Dr. Jason A. Efstathiou, a radiation oncologist at Massachusetts General Hospital, which has been delivering proton therapy since the 1940s, says that the findings are in line with those of other comparative studies, some showing a modest early benefit in terms of adverse events for proton beams, and others showing an advantage for IMRT over proton therapy or conformal radiation in patients with prostate cancer.
"There are results out there supporting differences, largely modest differences, between radiation therapy types, but they’re kind of all over the map," he said in an interview.
For example, he and colleagues presented data from a prospective study at the 2012 ASCO Genitourinary Cancers Symposium showing that in patient-reported quality of life domains, "PBT appears to be associated with lower gastrointestinal and urinary toxicity early after treatment, with similar late outcomes," they wrote.
In a different study, published in April 2012 in JAMA, investigators at the University of North Carolina in Chapel Hill found that "among patients with nonmetastatic prostate cancer, the use of IMRT compared with conformal radiation therapy was associated with less gastrointestinal morbidity and fewer hip fractures, but more erectile dysfunction; IMRT compared with proton therapy was associated with less gastrointestinal morbidity" (JAMA 2012;307:1611-20).
To get a better handle on this complex issue, Massachusetts General Hospital, in partnership with the University of Pennsylvania, is embarking on a randomized study of the comparative efficacy and safety of PBT vs. IMRT. The study will look at 6-month efficacy outcomes, cost effectiveness and toxicities at 2 years, and survival and other end points out to 10 years. Dr. Efstathiou is the principal investigator of that study. He was not involved in the study by Dr.Yu and his colleagues.
The current study was conducted with assistance from the Centers for Medicare and Medicaid Services. Dr. Yu and Dr. Efstathiou reported having no relevant disclosures.