Prostate-specific antigen kinetics after stereotactic body radiotherapy for localized prostate cancer: A scoping review and meta-analysis.

Purpose: Stereotactic body radiotherapy (SBRT) is emerging as a valuable treatment modality for localized prostate cancer, with promising biochemical progression-free survival rates. Longitudinal assessment of prostate-specific antigen (PSA) is the mainstay of follow-up after treatment. PSA kinetics and dynamics are well-established in the context of brachytherapy and conventionally fractionated radiotherapy, yet little is known in the context of prostate SBRT.

Methods: A review of available literature in MEDLINE, Scopus, and Embase was performed, focusing on studies reporting PSA slope, nadir, bounce, and biochemical failure after prostate SBRT.

Results: Thirty-three records (45 % prospective) encompassing 9,949 patients were included. SBRT dose ranged from 32-50 Gy in 4-5 fractions and overall median follow-up time (range) was 41 (15-74) months. Use of androgen deprivation therapy ranged from 0-38 %. SBRT was characterized by a steep initial decline of PSA, slowing down over time and ultimately yielding a lower nadir in comparison with conventional radiotherapy, with a median value (range) of 0.24 (0.1-0.6) ng/mL after a median time (range) of 33.1 (6-54) months. There was an inverse correlation between the highest SBRT dose in a trial and PSA nadir (r = - 0.59; p < 0.001). Benign PSA bounce occurred in 30 % of patients across all studies, after a median time (range) of 14.8 (9-36) months and with a median size (range) of 0.5 (0.3-1.1) ng/mL. There was no significant correlation between bounce and dose, nadir nor biochemical failure. There was, however, a significant inverse correlation between ADT use and PSA bounce frequency (r = -0.49; p = 0.046).

Conclusion: PSA kinetics and dynamics after SBRT for localized prostate cancer are different from those in other established radiotherapy modalities. Benign PSA bounce is very common. Clinicians should be aware of these factors and patients should be counseled accordingly, preventing unnecessary distress or salvage treatment.