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Conventional Versus Stereotactic Proton Therapy for Early-Stage Prostate Cancer

By: Celeste L. Dixon
Posted: Thursday, October 26, 2023

In low-risk, early-stage prostate adenocarcinoma, stereotactic body proton therapy (SBPT) has been found to be noninferior to conventionally fractionated proton therapy (CFPT) regarding freedom from failure, and the two therapies have similar long-term toxicity rates and health-related quality-of-life scores, according to the final analysis of the randomized, multicenter phase III PCG GU002 trial presented at the 2023 American Society for Radiation Oncology (ASTRO) Annual Meeting (Abstract 140). Of 133 patients enrolled in the trial—all followed for at least 2 years and for a median of 5 years—45 were randomly assigned to CFPT and 88, to SBPT, reported Diego A.S. Toesca, MD, of the Mayo Clinic, Phoenix, and colleagues.

Patients in the CFPT arm received 79.2 Gy in 44 fractions for 9 weeks; those randomly assigned to SBPT received 38 Gy in 5 fractions for 1 week. Concurrent or adjuvant androgen-deprivation therapy (ADT) was not allowed.

For both groups, the 2-year rate of freedom from failure was 100%, which fulfilled the prespecified criteria for noninferiority of SBPT compared with CFPT, explained the authors. Freedom from failure at 2 years was defined as the first instance of local, regional, or distant recurrence; biochemical failure; or the start of salvage therapy, including ADT.

For patients treated with CFPT and SBPT, respectively, the 5-year freedom-from-failure rates were 97.4% and 100% (P = .1), and the 5-year overall survival rates were 97.1% and 95.5% (P = .46). The cumulative incidence of any grade 3 toxicities at 5 years was 0% and 5.7% (P = .14), respectively. The frequency of gastrointestinal grade 2 toxicity at 6 months was 0% and 2.3% (P = .55), respectively; at 2 years, it was 6.7% and 3.4% (P = .69). The frequency of genitourinary grade 2 toxicity at 6 months was 2.2% and 5.7% (P = .42), respectively, and at 2 years, it was 8.9% and 5.7% (P = .54). Changes in health-related quality-of-life scores (including urinary, bowel, sexual, and hormonal evaluations) at 2 years were similar between groups.

Disclosure: Dr. Toesca reported no conflicts of interest.

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