No abstract

Following radiotherapy, PSA nadir is correlated with disease-free survival-lower nadir predicting higher long-term biochemical disease-free rates; however, temporary PSA rise ("bounce") may confound this prediction. We present mature results from a prospective Phase II SBRT trial correlating PSA response kinetics with relapse, with detailed analysis of patients with any post-SBRT PSA rise. Materials/Methods: 17 institutions treated 259 low-and intermediate-risk patients with SBRT (38Gy/4 fx) with median and maximum post-SBRT follow-up of 5 and 8 years. "Heterogeneous" dosimetry was required: Dmax >150% of prescribed (Rx isodose 50-67%), with strict "HDR-like" urethra, bladder and rectal dose limitation. Androgen deprivation therapy was not used. Patients were considered biochemically relapsed if either Phoenix or ASTRO criteria were met. Results: Median PSA levels measured 5.12 ng/mL pre-SBRT and 0.9, 0.2, 0.1 and 0.055 ng/mL at 1, 3, 5 and 7 years post-SBRT, respectively. Although 93.2% of patients remained disease-free at 5-and 7-years (100% low risk, 88.5% int. risk; nadir + 2), only 35% (90/259) had continuously decreasing PSA values post-SBRT, while 65% (169/259) had at least one rise (median 0.2 ng/mL; range 0.1-4.2 ng/mL). Of patients with any post-SBRT PSA rise, only 15/169 (8.9%) developed confirmed biochemical relapse (CBR), while 154/169 (91.1%) remained disease-free. Among patients with any PSA rise, those with CBR had a higher median PSA nadir (2.2 vs 1.2 ng/mL for non-relapsers, pZ0.046), and shorter median time to 1 st rise (16 vs 23 months for non-relapsers, pZ0.03). Median magnitude of first PSA rise was similar: 0.2 ng/mL for both. Among patients with any PSA rise, additional factors associated with relapse are in the Table. Conclusion: After heterogeneous SBRT, median PSA decreases through 7 years of follow-up, reaching <0.1 ng/mL after year 6. Nearly 2/3rds of patients experienced at least one post-SBRT PSA rise, with over 90% remaining disease-free thereafter. PSA rise associated with biochemical relapse tended to occur sooner and have a higher pre-bounce nadir level and was also more commonly seen in older patients and those with nonlow-risk disease. These results may help physicians to better sort patients whose post-SBRT PSA rise is unlikely to portend relapse versus those who may require more intensive monitoring.