Studies: Proton therapy effective treatment for prostate cancer

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Two studies published in the January issue of the International Journal of Radiation Oncology•Biology•Physics demonstrated the effectiveness of proton therapy in treating prostate cancer. One study revealed the therapy’s effectiveness while limiting side effects; the other showed that external beam therapy can achieve results comparable to brachytherapy.

In the first study, researchers at the University of Florida Proton Therapy Institute in Jacksonville, led by Nancy Mendenhall, MD, wanted to examine outcomes, including toxicity, in image-guided proton therapy. According to the study background information, while x-ray-based radiation therapies have been successful, an opportunity still remains to lower toxicity by reducing unnecessary radiation dose to non-targeted tissues.

“Increased toxicity with dose escalation and intensification efforts, particularly gastrointestinal toxicity and genitourinary (GU) toxicity, suggests that we have approached the maximum therapeutic ratio with x-ray–based EBRT [external-beam radiation therapy],” wrote the authors. “Most radiation energy in patients receiving x-ray–based EBRT is deposited in non-targeted tissue; in contrast, most radiation energy with external-beam proton therapy is deposited inside the targeted area.”

Researchers prospectively studied 211 men with low-, intermediate- and high-risk prostate cancer. After the men were treated with proton therapy, one intermediate-risk patient and two high-risk patients showed disease progression.

Side effects at follow-up were limited as well. The study results showed that 42 percent of patients required post-treatment GU symptom management compared with 38 percent who needed symptom management pre-treatment. Four transient Grade 3 GU toxicities occurred, but all were among patients with pre-treatment symptoms. Only one Grade 3+ gastrointestinal symptom occurred.

"This study is important because it will help set normal tissue guidelines in future trials," said Mendenhall.

In the second study, researchers from Massachusetts General Hospital in Boston, Loma Linda University Medical Center in Loma Linda, Calif., and the Radiation Therapy Oncology Group in Philadelphia performed a case-matched analysis comparing high-dose external-beam radiation therapy using a combination of photons and protons with brachytherapy.

Over three years, 196 patients received the external beam treatments of 79.2 Gray equivalent dose using photons and protons. Data were compared to 203 men of similar stages who received brachytherapy over the same time period. Researchers then compared the biochemical failure rates.

Eight-year biochemical failure rates were 7.7 percent for external-beam radiation therapy patients and 16.1 percent for brachytherapy patients. When stratified by risk group, the biochemical failure rates were similar with either technique, according to the study results.

"For men with prostate cancer, brachytherapy and external beam radiation therapy using photons and protons are both highly effective treatments with similar relapse rates," wrote John J. Coen, MD, a radiation oncologist at Massachusetts General Hospital. "Based on this data, it is our belief that men with prostate cancer can reasonably choose either treatment for localized prostate cancer based on their own concerns about quality of life without fearing they are compromising their chance for a cure."