ESTRO 2023 - Abstract Book

S1178

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ESTRO 2023

In this single institutional analysis, we prospectively collected fiducial tracking information for patients who were treated with upfront conventionally fractionated pelvic nodal radiation followed by a 3-fraction boost. As a control group, during the same period we identified patients treated sans nodes with 5-fraction SBRT. Monte Carlo estimates (MC) to the Fisher’s Exact Test was used to assess temporal loss of fiducial tracking across treatment fractions. Volatility was defined as a deviation from the most common “state” of fiducial tracking, and was corrected for number of fractions. The 5- and 3 fraction cohorts were compared using the Mann-Whitney Test (MWT). Analysis of fiducial tracking changes and their association with pre-treatment factors was performed using two techniques: (1) pattern of tracking change from first to last fraction using the Kruskal-Wallis test and MC, and (2) deviation from ideal tracking as a function of fiducial tracking loss aggregated over all fractions using Spearman Correlation Coefficient and MWT. Results A total of 233 patients were treated with either 5-fraction SBRT (n = 186, 79%) or a 3-fraction SBRT boost after nodal irradiation (n = 49, 21%) from April 2021 to July 2022. Over five treatment fractions, there was a significant (p < 0.001) loss of fiducial tracking fidelity as demonstrated by progressive loss of one tracked fiducial. In contrast, there was no similar tracking loss for the three fraction regimen that proceeded nodal treatment (p = 0.9). Moreover, there was significantly more volatility observed in the 5-fraction versus 3-fraction boost treatment (median volatility 2.2 vs. 0.0, p < 0.001). There were no significant associations between fiducial tracking, independently for 3- or 5-fractions, using either analysis method for the following parameters: neoadjuvant ADT, time from fiducial placement to SBRT, clinical target volume, and QOD vs. daily SBRT delivery. Conclusion Pelvic nodal treatment has no impact on 3-fraction SBRT boost fiducial tracking quantity or quality. In contrast, 5-fraction treatments demonstrated a significant progressive loss of fiducial tracking over time and increased volatility of those fiducials tracked, thus we recommend placement of a minimum of four fiducials. Finally, no pre-treatment factors were significantly associated with changes in fiducial tracking for 3- or 5- fraction SBRT. G.C. Iorio 1 , E.M. Cuffini 1 , V. Chiofalo 1 , C. Grossi 1 , S. Bartoncini 1 , V. Richetto 2 , I. Bonavero 1 , D. Bongiovanni 1 , G. Petruzzellis 1 , M. Levis 1 , G. Rovera 3 , S. Grimaldi 3 , B. Lillaz 4 , M. Oderda 4 , P. Gontero 4 , D. Deandreis 3 , U. Ricardi 1 1 University of Turin, Department of Oncology, Turin, Italy; 2 University of Turin, Department of Medical Physics, Turin, Italy; 3 University of Turin, Department of Medical Sciences, Nuclear Medicine, Turin, Italy; 4 University of Turin, Department of Surgical Sciences, Urology, Turin, Italy Purpose or Objective To evaluate the impact of PSMA-PET in the management of oligorecurrent post-prostatectomy (RP, +/- prostate bed RT) prostate cancer (PCa) patients, with a focus on metastasis-directed therapy (MDT),namely SBRT. Materials and Methods This analysis is part of a prospective, open label, observational, single-centre study testing the PSMA-PET performance in recurrent hormone-sensitive PCa patients. Patients with biochemical recurrence (BCR, PSA>0.2 ng/ml) following RP +/- prior prostate bed RT (PB-RT, adjuvant-ART or salvage-SRT) were staged with PSMA-PET. This analysis pertains to PSMA positive patients only. The primary endpoint was to assess the biochemical progression-free survival (bPFS) resulting from the therapeutic approaches employed for the different recurrent sites; patients with an exclusive PB-recurrence and no prior PB-RT were excluded from the analysis. The ADT-free interval was evaluated in patients treated with exclusive SBRT. Results Data from 193 patients staged with PSMA-PET (June 2016-April 2022) for BCR after RP (pN0-pNx) were prospectively collected. Median follow-up was 38.8 months (mos). 89/193 PSMA-positive patients (46.11%) were included in the present analysis, with 155 lesions detected. 7 patients with an exclusive PB-recurrence and no prior PB-RT were excluded from the analysis. The most common failure site was N1, with 57 lesions detected in 33 patients (37%); 10 patients (11.3%) had M1a, 21 (23.6%) had M1b, 3 patients (3.4%) had M1c, while 14 patients (15.7%) had multiple lesions. Tables 1-2 show patient, PSMA and treatment details. Hereby, we report mainly the MDT cohorts outcomes per recurrent site. In 22/89 cases (24.7%) SBRT + ADT was administered: 13 N1, 2 M1a, 6 M1b, 1 N1+M1b. The median bPFS of this cluster was 9.9 mos (range 3 – 39.5), and 12/22 patients recurred after median interval of 9.5 mos. Exclusive SBRT was administered in 16/89 patients (17.9%): 8 N1, 1 M1a, 7 M1b. The median bPFS was 8.3 mos (range 3.5 - 42), with 13/16 patients recurring after a median interval of 7.8 mos (range 3.5 – 30). After a median interval of 19.5 mos, 6/13 patients underwent a second SBRT round (+ADT in 3/6 patients) achieving a median bPFS of 8.3 mos (1 – 23.3). 1/13 patients underwent exclusive ADT. An observational approach was adopted in 6/13 cases, contributing to an overall median ADT-free interval of 31.2 mos. 5/89 patients (5.6%) underwent salvage surgery (4 N1, 1 M1a) with a median bPFS of 6.6 mos (range 1 – 11.7). 26/89 patients underwent exclusive ADT following positive PSMA findings, and at the present analysis only 2 developed castration resistance. PO-1456 PSMA-guided management of oligorecurrent post-prostatectomy patients: focus on SBRT