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For post-prostatectomy radiotherapy (RT), use of a hypofractionated regimen was noninferior to conventional RT in terms of patient-reported gastrointestinal or genitourinary (GI/GU) toxicities, a phase III study demonstrated.

The NRG Oncology GU-003 trial met its co-primary endpoints, with no clinically or statistically significant differences between arms on the Expanded Prostate Cancer Index Composite (EPIC) for both GI or GU toxicities at 2 years (P=0.12), reported Mark Buyyounouski, MD, of Stanford University in California.

For the hypofractionated versus conventional RT arms, respectively, mean changes from baseline on the EPIC GI and GU domains at this time point were:

• GI toxicities: -2.2 (±13.2) vs -1.5 (±14.1)
• GU toxicities: -5.2 (±22.8) vs -3.0 (±23.3)

"HYPORT [hypofractionated post-prostatectomy radiotherapy] represents a new practice standard for patients receiving post-prostatectomy radiotherapy," said Buyyounouski during a press briefing at the annual meeting of the American Society for Radiation Oncology (ASTRO).

At the completion of RT, the average change in GI scores was significantly worse for the hypofractionated RT group (-15.0 [±21.3]) compared to the conventional RT group (-6.8 [±15.8]; P=0.0011), but these differences vanished as time went on. No significant differences were seen for GU scores at RT completion (-7.9 [±20.9] and -4.3 [±22.6], respectively; P=0.70), or at any point thereafter.

At a median follow-up of 2.1 years, there was no difference between groups for biochemical or local failure.

While this was a noninferiority study about hypofractionation, "it is also a study about quality of life," said Buyyounouski. "It will be important for any new practice standard to preserve quality of life for patients."

Buyyounouski noted that hypofractionation is used every day in treating intact prostate cancer, but the researchers wanted to evaluate whether it could also be an appropriate option for men after they've undergone prostatectomy.

"This is an area of unmet need," said ASTRO discussant Sophia Kamran, MD, of Massachusetts General Hospital Cancer Center in Boston, who called the findings "potentially practice changing."

She noted that multiple potential benefits can be realized if hypofractionated RT can be extended to post-prostatectomy patients, from time savings and added convenience for patients, to more efficient utilization of resources in radiology departments.

"The field is moving toward hypofractionated radiotherapy for prostate cancer, and it really has been widely accepted in the intact setting," Kamran said. "Using contemporary radiation techniques and image guidance, we are able to target a volume and are able to safely deliver hypofractionated radiation therapy that allows for multiple benefits on multiple fronts for our patients, and for our physicians as well."

NRG Oncology GU-003 randomized 296 patients to either hypofractionated RT (62.5 Gy to the prostate bed in 25 fractions of 2.5 Gy) or conventional RT (66.6 Gy in 38 fractions of 1.8 Gy). Patients were eligible for the study if they had an undetectable PSA (<0.1 ng/mL) with either margin-negative pT3pN0/X or margin-positive pT2pN0/X adenocarcinoma of the prostate, or a detectable PSA (≥0.1 ng/mL) but pT2/3pN0/X disease.

"There was a lot of enthusiasm for this trial," said Buyyounouski. "We accrued 294 patients in 1 year and we think this demonstrated the enthusiasm both on behalf of patients and physicians in adopting a new approach like this."

Patients were stratified according to baseline EPIC scores and whether or not they had received androgen deprivation therapy. Changes in EPIC GU and GI domains were assessed at completion of RT, and at 6, 12, and 24 months.

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