Early PSA kinetics for low- and intermediate-risk prostate cancer treated with definitive radiation therapy.

Abstract

PURPOSE\nThis study uses a patient-specific model to characterize and compare ideal PSA kinetics for low- and intermediate-risk prostate cancer following definitive radiation treatment with conventionally fractionated (CFRT), hypofractionated (HFRT), stereotactic body radiation therapy (SbRT), or brachytherapy, both high-dose-rate (HDR) and low-dose-rate (LDR).\n\n\nMETHODS AND MATERIALS\nThis retrospective analysis includes low- and intermediate-risk prostate cancer patients treated between 1998 and 2018 at an NCI-designated Comprehensive Cancer Center. Demographics and treatment characteristics were prospectively collected. Patients had at least two PSA measurements within 24-months of treatment and were free from biochemical recurrence. The incidence of, time to, and risk factors for PSA nadir (nPSA) and bounce (bPSA) were analyzed at 24-months following radiotherapy. Ideal PSA kinetics were characterized for each modality and compared.\n\n\nRESULTS\nOf 1,042 patients, 45% had low-risk cancer, 37% favorable intermediate-risk, and 19% unfavorable intermediate-risk. nPSA were higher for ablative modalities, both as absolute nPSA and relative to initial PSA (iPSA). Median time to nPSA ranged from 14.8 to 17.1 months. Over 50% treated with non-ablative therapy (CFRT, HFRT, and LDR) reached an nPSA threshold of ≤0.5 ng/mL compared to 23% of SbRT and 33% of HDR cohorts. The incidence of bPSA was 13.3% and not affected by treatment modality, Gleason Score, or prostate volume. PSA decay rate was faster for ablative therapies in the 6-24 month period.\n\n\nCONCLUSIONS\nAnalysis of PSA within 24-months following radiation therapy revealed ablative therapies are associated with a latent PSA response and higher nPSA. Multivariable logistics modeling revealed younger age, iPSA above the median, presence of bPSA, and ablative therapy as predictors for not achieving nPSA ≤0.5 ng/mL. PSA decay rate appears to be faster in ablative therapies following a latent period. Understanding the different PSA kinetic profiles is necessary to assess treatment response and survey for disease recurrence.