Two studies published in International Journal of Radiation Oncology*Biology*Physics indicate that proton therapy is a useful treatment for prostate cancer. This specialized form of external-beam radiation therapy (EBRT) employs protons rather than x-rays.

One set of researchers followed 211 men with low-, intermediate-, or high-risk prostate cancer who were participating in three prospective trials of image-guided proton therapy. The patients were followed for a minimum of 2 years.

Disease progression occurred in one intermediate-risk and two high-risk patients. In the pretreatment period, 38% of patients required genitourinary (GU) symptom management compared with 42% posttreatment. A total of four transient Grade 3 GU toxicities occurred, all among the men requiring pretreatment GU symptom management. The researchers found a correlation between posttreatment GU 2+ symptoms and pretreatment GU symptom management.

Only one Grade 3+ gastrointestinal (GI) symptom occurred. The prevalence of Grade 2+ GI symptoms was 0% at 6 months, 5% at 12 months, 6% at 18 months, and 4% at 24 months, with a cumulative incidence of 20 patients (10%) 2 years after proton therapy. Grade 2+ rectal bleeding and proctitis correlated significantly with the percentage of rectal wall receiving proton therapy doses ranging from 40 cobalt gray equivalent (CGE) to 80 CGE.

“Early outcomes with image-guided proton therapy suggest high efficacy and minimal toxicity with only 1.9% Grade 3 GU symptoms and [less than] 0.5% Grade 3 GI toxicities,” concluded the investigators (Int J Radiat Oncol Biol Phys. 2012;82[1]:213-221; www.redjournal.org/article/S0360-3016%2810%2903332-8/fulltext).

In the same journal issue, a team led by radiation oncologist John J. Coen, MD, of Massachusetts General Hospital in Boston, described the results of high-dose EBRT using a combination of photons (x-rays) and protons for localized prostate cancer in 196 men, compared with permanent prostate brachytherapy in 203 case-matched patients (pp. e25-e31; www.redjournal.org/article/S0360-3016%2811%2900206-9/fulltext).

Although the 8-year biochemical failure (BF) rates were 7.7% in the EBRT group and 16.1% in the brachytherapy group, BF rates were similar by either technique when stratified by patient-risk group.