3327 - Characteristics and Prognostic Implications of PSA Bounce in Prostate Cancer Patients Treated with Stereotactic Body Radiotherapy (SBRT)
Presenter(s)
A. Romei1, L. Nicosia2, C. Orsatti1, A. G. Allegra1, E. Pastorello1, F. Ricchetti1, N. Giaj-Levra1, C. De-Colle1, M. Rigo1, R. Ruggieri2, and F. Alongi1; 1Department of Advanced Radiation Oncology, IRCSS "Sacro Cuore Don Calabria Hospital" Cancer Care Center, Negrar di Valpolicella (VR), Italy, 2Department of Advanced Radiation Oncology, IRCCS Sacro Cuore Don Calabria Hospital, Cancer Care Center, Negrar di Valpolicella, Italy
Purpose/Objective(s): Prostate-specific antigen bounce (PSAb), a transient elevation in PSA levels, is an uncommon event observed in prostate cancer (PC) patients undergoing radiotherapy, causing potential diagnostic misinterpretation with biochemical recurrence. Furthermore, the etiology and kinetics of PSAb are not well known yet. This study analyzes the incidence, characteristics, and clinical relevance of PSAb in a homogeneous cohort of PC patients treated with stereotactic body radiotherapy (SBRT).
Materials/Methods: PC Patients received five SBRT fractions (35-36.25 Gy total) using the 1.5T MR-Linac platform with an adaptive workflow based on pre-treatment MRI images and cine-MRI monitoring. Inclusion criteria included men with a WHO performance status =2, low to intermediate-risk PC (stage T1-T2, Gleason =4+3), and absence of metastases. PSA levels were monitored to identify PSAb.PSAb was defined as a transitory increase of PSA level during the follow-up more than 0,2 mg/ml from previous PSA nadir. Statistical analysis examined correlations between the PSAb and various clinical and dosimetric variables. The Chi-square test was used for categorical variables (e.g., SpaceOAR use, radiation dose, treatment site, and Gleason Score), while Spearman’s correlation coefficient assessed continuous variables (e.g., initial and final tumor volumes, IPSS, and changes in CTV from first to the last fraction). Linear regression analysis further explored the impact of tumor volume changes (CTVdelta), post-bounce nadir, acute and chronic toxicity.
Results: 301 patients treated with SBRT were included in the analysis. PSAb occurred in 24.6% of patients, after a median of 11 months post-treatment, and 6 months PSAb incidence was 86.4%. No significant associations were found with tumor volume metrics or treatment scheduling. PSAn occurred after a median of 16 months and the mean PSAn was 1.02ng/ml (0.006-5.02ng/ml). Biochemical relapse occurred in 9 patients (3%).Toxicity analysis revealed predominantly acute events (G1-2), including cystitis (27.5%) and proctitis (4.6%), with minimal late toxicity, such as cystitis (9.2%) and sexual impotence (4.3%). No significant associations were found with toxicity. In the univariate analysis PSAb were correlated with biochemical relapse-free survival (p=0.01).
Conclusion: The identified correlations with treatment-specific factors offer insights into optimizing patient management and tailoring follow-up protocols. In this experience PSAb is associated with better oncological outcomes. Future research should explore the biological mechanisms of PSAb and its impact on long-term outcome emphasizing the need for careful post-treatment monitoring of PSA levels to differentiate PSAb from recurrence, thereby avoiding premature interventions.