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SAN ANTONIO -- Men with intermediate- and high-risk prostate cancer treated with external-beam pelvic radiotherapy (EBRT) had better quality of life (QOL) outcomes when the combined prostate brachytherapy boost had a high dose rate (HDR), according to research presented here.

In a randomized phase III trial comparing health-related QOL outcomes after either low dose rate (LDR) or HDR brachytherapy boost, researchers found that HDR patients had better urinary and bowel QOL domain scores at 3 and 6 months post-implant.

The improved bowel domain scores persisted up to 48 months, reported Nikitha Moideen, MD, of BC Cancer Agency in Kelowna, British Columbia, at the annual meeting of the American Society for Radiation Oncology (ASTRO).

"We also saw an unexpected late decline in bowel quality of life at 24-48 months for LDR patients," Moideen said during the session. "We are currently doing an analysis of rectal dose for dose response relationships to try to explain this decline."

ASTRO session panel discussant Sophia C. Kamran, MD, of Massachusetts General Hospital in Boston, noted the advantage for patient experience with the HDR brachytherapy boost technique.

"We need to wait for efficacy data, but this gives us a lot of information," Kamran told attendees. "If you see a patient for whom you want to use combined therapy, and they are concerned about GI or GU toxicity, or quality of life, we can incorporate HDR brachytherapy."

The study included 191 men (42% with intermediate-risk prostate cancer and 58% with high-risk disease) with a median age of 71 years. Of these patients, 74% received androgen deprivation therapy for a median duration of 12 months. All received pelvic EBRT combined with prostate brachytherapy and were randomized to a 110 or 15 Gy boost.

The study's primary endpoint was acute urinary QOL at 6 months post-implant, measured with the Expanded Prostate Cancer Composite questionnaire. Secondary endpoints included acute bowel and urinary QOL at 6 months as well as late urinary, bowel, and sexual QOL at 1- to 5- year time points.

Moideen and her colleagues found that urinary QOL scores worsened more from baseline for HDR patients at 1 month, with declines from 88 to 74 compared with 89 to 81 for LDR patients.

"It is no surprise that HDR patients report earlier onset of symptoms," Moideen said. "By month 1, these patients have received their HDR implants and are well into their external beam radiation [treatment] portion, and at this point in time they report worse quality of life compared with LDR patients. However, by months 3 to 6, LDR patients have received a significant portion of their brachytherapy dose and report a worse quality of life than HDR patients."

Specifically, HDR patients QOL urinary domain scores rebounded to 79.0 versus 69.4 for LDR patients at 3 months and 84.0 versus 76.9 at 6 months (both P<0.001).

"LDR patients improved by month 12, and there's absolutely no difference in late urinary quality of life at 12 months to 60 months," Moideen reported.

As with urinary QOL scores, HDR patients also had higher bowel QOL scores at 3 months (87.0 vs 82.1, P=0.005) and 6 months (88.7 vs 82.8, P=0.023). However, while HDR patients were able to sustain those higher QOL scores up to 48 months, LDR patients did not improve late bowel QOL scores relative to the scores of HDR patients.

There was no statistically significant difference in health-related QOL sexual domain scores between the two arms.

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