IMRT for Prostate Cancer: Standard Confirmed

Comparative Effectiveness Research

Nick Mulcahy

April 18, 2012

April 18, 2012 — The current radiotherapy standard for the treatment of localized prostate cancer — intensity-modulated radiation therapy (IMRT) — is the right standard, according to a study published in the April 18 issue of JAMA.

"IMRT causes fewer side effects and achieves better cancer control than the older conformal radiation," said senior author Ronald Chen, MD, MPH, from the University of North Carolina in Chapel Hill. He spoke at a press conference, held in Washington, DC, on the journal's new issue, which centers on comparative effectiveness research.

Currently there is "no clear evidence" that the newest and most expensive radiation technology — proton therapy — is better than IMRT, he said, adding that a randomized trial is needed to evaluate the 2 approaches.

To compare radiotherapy approaches, Dr. Chen and colleagues used population-based data, from 2000 to 2009, from the Surveillance, Epidemiology, and End Results (SEER) program, which are linked to Medicare claims.

The outcome measures were treatment-related morbidities and the need for any additional cancer therapy.

The main findings were that IMRT was associated with less need for additional therapy, fewer adverse bowel effects and hip fractures, but more erectile dysfunction than conformal radiation.

In addition, IMRT was associated with fewer adverse bowel effects than proton therapy, but there were no significant differences in other adverse effects or in the need for additional cancer treatment.

The researchers also found that the use of IMRT skyrocketed during the study period, growing from 0.15% of radiation cases in 2000 to 95.90% in 2009.

This "almost complete adoption" of IMRT took place despite the fact that no study had compared nongastrointestinal morbidity and disease control outcomes between conformal radiation therapy and IMRT, write the researchers. One single-center study did compare the 10-year rate of gastrointestinal morbidity, and found IMRT to be superior to conformal therapy, they add.

"What we saw in our study was that physicians adopted a new technology before there was a lot of evidence showing its effectiveness," Dr. Chen said. "Now we are seeing a similar trend with proton therapy," he added.

Dr. Chen sketched out the state of affairs with proton therapy in the United States.

Until 2006, there were 3 proton centers. In the past 5 years, that number has tripled, he said. Additionally, an estimated 20 more centers, which cost about $150 million, are in the building or planning stages. Medicare pays about $48,000 for each individual undergoing proton therapy, compared with $20,000 for IMRT, Dr. Chen pointed out.

A prominent oncologist recently decried the lack of evidence supporting the superiority of proton therapy over IMRT, and its cost.

Ezekiel Emanuel, MD, from the University of Pennsylvania in Philadelphia, and a former adviser to President Barack Obama, described the ongoing building of proton-beam therapy units in the United States as a "medical arms race" and "crazy medicine and unsustainable public policy."

In a recent New York Times online opinion piece, Dr. Emanuel wrote: "If the United States is ever going to control its healthcare costs, we have to demand better evidence of effectiveness and stop handing out taxpayer dollars with no questions asked."

Fewer Adverse Events With IMRT

For their comparison of IMRT and conformal radiation therapy, the researchers excluded any men in the SEER database who received radiation in combination with brachytherapy or prostatectomy. They found 12,976 men who received treatment from 2002 to 2006. Of these, 6666 received IMRT and 6310 conformal radiation; median follow-ups were 44 and 64 months, respectively.

In propensity-score-adjusted analyses, men who received IMRT were less likely than men who received conformal radiation therapy to receive a diagnosis of gastrointestinal morbidities (absolute risk, 13.4 vs 14.7 per 100 person-years; relative risk [RR], 0.91; 95% confidence interval [CI], 0.86 to 0.96) or hip fracture (absolute risk, 0.8 vs 1.0 per 100 person-years; RR, 0.78; 95% CI, 0.65 to 0.93).

The IMRT-treated patients were also less likely to need an additional cancer therapy (absolute risk, 2.5 vs 3.1 per 100 person-years; RR, 0.81; 95% CI, 0.73 to 0.89), but more likely to receive a diagnosis of erectile dysfunction (absolute risk, 5.9 vs 5.3 per 100 person-years; RR, 1.12; 95% CI, 1.03 to 1.20).

For the comparison of proton therapy and IMRT, the researchers identified 684 men treated with proton therapy from 2002 to 2007. They say that this is the largest series of patients to receive proton therapy to date.

They used propensity-score matching to compare these 684 patients treated with proton therapy and 684 treated with IMRT; median follow-ups were 50 and 46 months, respectively. IMRT patients had a lower rate of gastrointestinal morbidity (absolute risk, 12.2 vs 17.8 per 100 person-years; RR, 0.66; 95% CI, 0.55 to 0.79).

The researchers speculate that "the higher vulnerability of proton therapy to organ movement...may lead to an unintentional higher dose to the rectum compared with IMRT."

In response to this study, ProCure Treatment Centers, a group of 3 centers that offers proton-beam therapy, issued a statement that contradicted the findings of adverse bowel effects, saying that "protons reduce — not increase — gastrointestinal side effects."

There were no significant differences in rates of other morbidities between IMRT and proton therapy, or in the need for additional therapies, the researchers conclude.

Funding for the study was provided by the Agency for Healthcare Research and Quality. The authors have disclosed no relevant financial relationships.

JAMA. 2012;307:1611-1620. Abstract

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