Final Analysis of a Phase III Controlled Randomized Study of Stereotactic Body Proton Therapy or Conventionally Fractionated Proton Therapy for Early Prostate Cancer: PCG GU002

PURPOSE/OBJECTIVE(S)

To determine if stereotactic body proton therapy (SBPT) is non-inferior to conventionally fractionated proton therapy (CFPT) in patients with early prostate cancer.

MATERIALS/METHODS

Multicenter, randomized, controlled, open-label, non-inferiority phase 3 trial that included patients with histologically confirmed low-risk prostate adenocarcinoma defined by Gleason score ≤6, PSA <10 ng/mL, and clinical stage T1-2a N0 M0 by AJCC 7th Ed. Eligible participants were randomly assigned (initially 1:1 and later 2:1 ratio) to CFPT (79.2 Gy in 44 fractions for 9 weeks) or SBPT (38 Gy in 5 fractions for 1 week). Concurrent or adjuvant androgen deprivation therapy was not allowed. The primary endpoint was freedom from failure (FFF) at 2 years, defined as the first occurrence of local, regional, or distant recurrence, biochemical failure by the Phoenix definition (increase of PSA ≥2 ng/mL over the nadir PSA), or the start of salvage therapy including ADT. Secondary endpoints included GI and GU grade ≥2 toxicity according to CTCAE v4 criteria, as well as health-related quality of life (HRQoL) metrics assessed by AUASI and EPIC scores. Non-inferiority would be declared if the 1-sided 95% confidence interval limit for the difference in 2-year FFF rate was below 4.2% between both groups by Clopper-Pearson exact method.

RESULTS

Between November 2010 and September 2020, 133 patients were enrolled and randomly assigned to CFPT (n = 45) or SBPT (n = 88). Median follow-up was 5 years (IQ 3.9-5.2), with the last patient enrolled followed for at least 2 years. The 2-year FFF was 100% for both groups, fulfilling the pre-specified criteria for non-inferiority of SBPT compared to CFPT. By KM estimates, 5-year FFF was 97.4% and 100% (P = 0.1), and the 5-year OS was 97.1% and 95.5% (P = 0.46) for patients treated with CFPT and SBPT, respectively. The cumulative incidence of any grade ≥3 toxicities at 5 years was 0% and 5.7% (P = 0.14) for patients treated with CFPT and SBPT, respectively. The frequency of GI grade ≥2 toxicity at 6 months was of 0% and 2.3% (P = 0.55), and at 2 years was of 6.7% and 3.4% (P = 0.69) for patients treated with CFPT and SBPT, respectively. The frequency of GU grade ≥2 toxicity at 6 months was of 2.2% and 5.7% (P = 0.42), and at 2 years was of 8.9% and 5.7% (P = 0.54) for patients treated with CFPT and SBPT, respectively. Changes in HRQoL scores at 2 years were similar between groups (Table).

CONCLUSION

SBPT is non-inferior to CFPT regarding FFF and associated with similar long-term toxicity rates and HRQoL metric scores.