ESTRO 2024 - Abstract Book

S2546

Clinical - Urology

ESTRO 2024

PSA level at imaging was not a useful discriminator for disease detection or presence of extraprostatic disease. Detection rates for any disease at levels 1-<2 ng/ml was 15/20 (75%), at 2-<3 ng/ml 14/18 (77.8%) and 3+ ng/ml 24/25 (96%), p = 0.19. Similarly, detection rates of extraprostatic disease were 14/20 (70%), 9/18 (50%) and 19/25 (76%) at these levels, p = 0.27. Analyzed by site of uptake, there was no difference in prostate, nodal, bone or visceral uptake based on PSA levels <2 or ≥ 2 ng/ml. Comparing patients with extraprostatic PSMA avid disease vs others, there was no difference in their PSA levels (median 2.7 vs 2.2 ng/ml, Mann-Whitney test p =0.65). However they had significantly shorter PSADT[prostate specific antigen doubling time] (median 3.9 vs 6.5 months, Mann-Whitney p = 0.01) and non-significantly higher proportion of Gleason grade group 4 and 5 disease [30(71.4%) vs 10(50.0%), chi-square p = 0.17]. PSADT < 3 months had significantly higher likelihood of extraprostatic disease detection 17/19 (89.5%) vs. 26/45 (57.8%), chi-square p = 0.03. Logistic regression model for extraprostatic disease detection based on PSA at the time of imaging, PSADT and Gleason grade group had a likelihood ratio chi- square of 10.84 with 5 df, and Pr(>χ2) of 0.05. The c -index was 0.74 and the R2 was 0.22. There was moderate calibration.

Conclusion:

PSMA PET-CT is a useful tool for identifying the patterns of recurrence at biochemical failure. The disease detection rate was high even at thresholds below 2 ng/ml, and a similar proportion of patients had metastatic disease above and below this threshold. Rather, patients with a shorter PSADT and higher Gleason grade group have a higher likelihood of metastatic disease at PSA progression and may be the ideal candidates for early imaging. Prospective studies are warranted to assess the impact of earlier imaging on outcomes.

Keywords: PSMA_PET, recurrence, prostate

2536

Mini-Oral

Long term outcomes of stereotactic MR-guided adaptive radiotherapy for prostate cancer

Claire van Vliet 1 , Philip Meijnen 1 , Anna H.M. Piet 1 , Paul Cobussen 1 , Berend J. Slotman 1 , Reindert J.A. van Moorselaar 2 , Anna M.E. Bruynzeel 1 1 Amsterdam UMC location Vrije Universiteit Amsterdam, Radiation Oncology, Amsterdam, Netherlands. 2 Amsterdam UMC location Vrije Universiteit Amsterdam, Urology, Amsterdam, Netherlands

Purpose/Objective:

Recently the use of stereotactic body radiotherapy (SBRT) has been implemented as standard treatment of localized prostate cancer. Stereotactic MR-guided adaptive radiotherapy (SMART) has shown superior toxicity outcomes compared to CT-guided SBRT and is well tolerated as confirmed by patient reported outcome measures (1, 2). This