Prostate-specific antigen kinetics in hypofractionated radiation therapy alone for intermediate- and high-risk localized prostate cancer.

Background: This study aimed to evaluate the treatment outcomes and define the prostate-specific antigen (PSA) kinetics as potential prognostic factors in patients with intermediate- or high-risk localized prostate cancer (PCa) who underwent moderately hypofractionated radiation therapy. Methods: The study retrospectively reviewed the medical records of 149 patients with intermediate- or high-risk localized PCa who underwent definitive radiation therapy (70 Gy in 28 fractions) without androgen deprivation therapy. Clinical outcomes were analyzed based on risk stratification (favorable-intermediate, unfavorable-intermediate, and high-risk). The biochemical failure rate (BFR) and clinical failure rate (CFR) were stratified based on the PSA nadir and the time to the PSA nadir to identify the prognostic effect of PSA kinetics. Acute and late genitourinary and gastrointestinal adverse events were analyzed. Results: Significant differences were observed in the BFR and CFR according to risk stratification. No recurrence was observed in the favorable intermediate-risk group. The 7-year BFR and CFR for the unfavorable intermediate-risk and high-risk groups were 19.2% and 9.8%, and 31.1% and 25.3%, respectively. Patients with a PSA nadir >0.33 ng/mL or a time to the PSA nadir <36 months had a significantly greater BFR and CFR. The crude rate of grade 3 late adverse events was 3.4% (genitourinary: 0.7%; gastrointestinal: 2.7%). No grade 4-5 adverse event was reported. Conclusion: A significant difference in clinical outcomes was observed according to risk stratification. The PSA nadir and time to the PSA nadir were strongly associated with the BFR and CFR. Therefore, PSA kinetics during follow-up are important for predicting prognosis.