Aim: to evaluate prevalence of prostate-specific antigen (PSA) bounce after high-dose rate interstitial radiation therapy as monotherapy for prostate cancer in two different regimens, and to perform an analysis of possible causes for this phenomenon.
Materials and methods: in 2012-2017 one hundred ninety eight prostate cancer patients underwent high-dose rate brachytherapy (HDR-BT) as monotherapy in N.N. Petrov National Medical Research Center of Oncology. Treatment was performed with one of two regimens: two 13 Gy sessions (group I) – 67 (33,8%) patients, and three 11,5 Gy sessions (group II) – 131 (66,2%) patients. Patients were treated using Microselectron device with Oncentra Prostate (Elekta) planning system (192Ir). All patients underwent 1 session of HDR-BT during 1 hospitalization with 1 fraction per 1 implantation with an average period between fractions being 3 weeks. PSA bounce was defined as PSA elevation to 0.3 ng/ml or above during its progressive decline after treatment completion with subsequent return to baseline (pre-bounce) or even lower values during surveillance or anti-inflammatory therapy.
Results: PSA bounce was observed in 61 (30,8%) patients out of 198. Depending on chosen HDR-BT regimen, transient PSA elevation was registered in 20 patients out of 67 in group I (29,8%) and in 41 patients out of 131 (31,3%) in group II. Four patients in group I and seven patients in group II had two separate PSA bounces. Duration of bounce-like PSA elevation was 3-6 months in most of the patients – 50 out of 61 (81,9%), and 6-9 months in the rest of the patients – 11 (18,1%). Calculations have shown that median prostate volume in patients who experienced PSA bounce was 48,7 cc [40,0; 60,4] (21,9-106,0), while in patients without PSA bounce in was equal to 31,4 cc [24,7; 38,2] (10,3-81,6) (р < 0,001).
Conclusion: PSA bounce was observed in almost one third of all patients without any relationship with HDR-BT fractioning regimen. Prostate volume was the main prognostic factor for PSA bounce.
Authors declare lack of the possible conflicts of interests.