Propensity-Weighted Survival Analysis of SBRT vs. Conventional Radiotherapy in Unfavorable Intermediate-Risk Prostate Cancer

BACKGROUND:Prostate stereotactic body radiotherapy (SBRT), which delivers high-dose precision treatment in ≤5 fractions, is a shorter, more convenient, and less expensive alternative to conventionally fractionated radiotherapy (CRFT; ∼44 fractions) or moderately hypofractionated radiotherapy (MFRT; 20-28 fractions). SBRT has not been widely adopted but may have radiobiologic advantages over CFRT/MFRT. We hypothesized that SBRT would be associated with improved overall survival (OS) versus CFRT or MFRT ± androgen deprivation therapy (ADT) for unfavorable-intermediate-risk prostate cancer (UIR-PCa). METHODS:Men with UIR-PCa treated with SBRT (35-40Gy in ≤5 fractions) or biologically equivalent doses of CFRT (72-86.4Gy in 1.8-2.0Gy/fraction) or MRFT (≥60Gy in 2.4-3.2Gy/fraction; biologically effective doses ≥120) were identified in the National Cancer Database (NCDB). Unweighted and propensity-weighted multivariable Cox analysis (MVA) was used to compare OS hazard ratios. RESULTS:Of 28,028 men with UIR-PCa who received CFRT with (n = 12,872) or without ADT (n = 12,984); MFRT with (n = 251) or without ADT (n = 281); and SBRT with (n = 212) or without ADT (n = 1,428) were identified. Relative to CFRT without ADT, CFRT+ ADT (HR 0.92, 95% CI 0.87-0.97, P = .002) and SBRT without ADT (HR 0.74, 95% CI 0.61-0.89, P = .002) were both associated with improved OS on MVA. Relative to CFRT+ADT, SBRT without ADT correlated with improved OS on MVA (HR:0.81, 95% CI 0.67-0.99, P = .04). Propensity-weighted MVA demonstrated that SBRT (HR:0.80, 95% CI 0.65-0.98, P = .036) and ADT (HR:0.91, 95% CI 0.86-0.97, P = .002) correlated with improved OS. SBRT was not associated with improved OS versus MFRT. CONCLUSION:SBRT, which offers a cheaper and shorter treatment course that mitigates COVID-19 exposure, was associated with improved OS versus CFRT for UIR-PCa. These results confirm guideline-based recommendations that SBRT is a viable option for UIR prostate cancer. The results from this large retrospective study require further validation in clinical trials.