Regina Elena National Cancer Institute Rome, Italy
L. Goanta1, I. Angelicone2, M. Bottero1, A. Farneti1, A. Faiella1, and G. Sanguineti1; 1IRCCS Regina Elena National Cancer Institute, Radiation Oncology, Rome, Italy, 2Sapienza University, Faculty of Medicine and Psychology, A.O.U SantAndrea, Radiation Oncology, Rome, Italy
Purpose/Objective(s): To investigate both the pattern of failure and the opportunity of a repeated radiotherapy course after salvage radiation therapy (sRT) for prostate cancer (PC). Materials/
Methods: At our Institution, all patients (pts) who develop a further biochemical failure (BF) after both radical prostatectomy and subsequent sRT are offered re-staging with prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) first, and, if negative, with multiparametric magnetic resonance imaging (mpMRI) of the prostatic fossa. In the present study we included the pts who satisfied all the following criteria since March 2023: no pathologically positive nodes at surgery; no distant disease at re-staging PET/CT before sRT; subsequent BF after sRT defined as Prostate-specific antigen (PSA) > 0.20 ng/ml on 2 consecutive measures; presence of recurrent disease at either PSMA PET/CT and/or mpMRI. Pts without detectable disease at imaging were disregarded. The site(s) of failure (FS) was (were) classified as Local (LS) if within the prostatic fossa, Regional (RS) if within the pelvic nodes up to the common iliacs excluded, and Distant (DS) if outside the pelvis. Oligorecurrence was defined as a maximum of 5 FS on imaging. After co-registering the positive re-staging imaging and the planning CT at sRT, we assessed whether each FS was outside (OFS) or inside (IFS) the previously treated volume and we estimated the mean equivalent dose in 2 Gy fraction (EDmean2) received by each IFS. Results: 56 consecutive pts were included. 29 (52%) pts had received prostatic fossa sRT only and 27 (48%) pts also whole pelvis sRT. Only 5 pts (9%) had undergone concurrent androgen deprivation therapy at sRT. Median PSA nadir after sRT was 0.06 ng/ml (IQR 0.01-0.3 ng/ml) and occurred after 7.8 months (IQR: 4-16.5 mths). All pts were restaged with PSMA PET/CT and 21 pts (38%) with mpMRI. We found an overall number of 83 recurrences at a median time of 41 months after sRT (IQR 19.9-65.2 mths). At failure, the median PSA was 0.63 ng/ml (IQR 0.4-1.2 ng/ml) and the median PSA doubling time was 8.3 months (IQR 4.3-12.3 mths). All patients were oligorecurrent. Failures were distributed as follows: 39 (47%) DS, 26 (31%) RS and 18 (22%) LS. 60 (72%) were OFS, whereas 23 (28%) were IFS; of the latter ones, 14 were LS, 7 RS and 2 DS, with a median EDmean2 of 75.2 Gy (IQR 73-78.7 Gy), 50 Gy (IQR 45.4-51.6 Gy) and 53.1 Gy (IQR 57.6-48.6 Gy), respectively. All LS had undergone a staging mpMRI at sRT and 13 (72%) occurred in a previously positive prostatic fossa. Conclusion: All patients are oligorecurrent at the time of a BF post-sRT. Moreover, most of the failures do occur outside a previously treated volume. For both reasons, a second course of definitive/ablative RT is potentially indicated. Surprisingly, the prostatic fossa is a relatively frequent site of failure especially when containing macroscopic disease and despite the high dosage at sRT.
