A PBRT update from the ASTRO annual meeting

Two papers presented at the annual meeting of the American Society for Radiation Oncology (ASTRO) offer some further information on the application of proton beam radiation therapy (PBRT) in treatment of prostate cancer.

In the first paper, Mendenhall and colleagues attempted to determine whether higher doses of proton beam radiation with proton therapy would cause early harmful side effects to urinary function within the genitourinary system (GU) function and rectal function within the gastrointestinal (GI) system.

This study reports data on 212 prostate cancer patients (enrolled between August 2006 and October 2007 in one of three prospective trials) all of whom received PBRT. High-risk patients also received docetaxol chemotherapy, followed by hormone therapy. The researchers followed the patients for at least a year after treatment and examined GU and GI toxicity scores  for each patient.

According to this report there was minimal early GU and GI toxicity on prospective trials of PBRTy. Less than 1 percent of patients had Grade 3 GU side effects, but there was a significant association between GU side effects after treatment and patients’ pretreatment urinary function. Less than 0.5 percent of patients had Grade 3 GI toxicities. The most common gastrointestinal side effect was minimal rectal bleeding, which was associated with the percentage of rectal wall receiving a range of radiation doses.

“Proton therapy is becoming more popular as a treatment for prostate cancer, but it is unclear at this point whether the long-term outcomes with proton therapy will be better than those achieved with other treatments,” Mendenhall is quoted as saying in an ASTRO media release. “These protocols were designed to establish benchmark results with proton therapy given with relatively high daily doses. At this point, we can say that early tolerance of proton therapy has been excellent, with a very low rate of urinary and rectal toxicity.” Dr. Mendenhall, is the medical director of the University of Florida Proton Therapy Institute in Jacksonville, FL.

According to a second ASTRO media release, Rossi and colleagues have reported that men who receive a “boost” of proton beam radiation after receiving a standard course of X-ray radiation therapy have fewer recurrences of their prostate cancer compared to men who did not receive the extra dose of proton radiation. Dr. Rossi is a radiation oncologist at the Loma Linda University Medical Center in Loma Linda, CA.

This study involved 391 patients with early-stage, localized prostate cancer treated at Loma Linda University Medical Center and Massachusetts General Hospital in Boston. Patients were randomized to receive either “standard dose” or “high dose” radiation, with proton beams being used to deliver the high-dose radiotherapy to the prostate. In low-risk patients, only 6 percent of those treated with high dose radiation had the cancer return after 10 years, compared to 29 percent who had conventional radiation doses. Among intermediate-risk patients, 37 percent who underwent high dose radiation had cancer come back, versus 45 percent of those who had conventional doses of radiation. There were no significant differences between the two groups in how long they survived and in their urinary and bowel functions.

It should be noted that the precise details of these two studies are not available in the media releases issued by ASTRO.

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