ESTRO 37 Abstract book

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ESTRO 37

Material and Methods In our retrospective study we evaluated 65 PC patients undergoing 68 Ga-PSMA-PET/CT or MRI in our department between March 2013 and December 2016 and consequently receiving dose escalation RT to PSMA- positive lesions, 4 patients with primary RT and 61 patients with biochemical failure (BCF) after RP +/- prior RT. Our data include 59 patients (90.7 %) with staging of high-risk PC and 5 patients with intermediate-risk PC. Overall median follow-up after dose escalation RT was 20.3 months (range 7.4-50.8mo). The primary endpoint was BCF after dose escalation RT. Toxicity rates were classified according to CTCAE v4.03. Results Median age at the beginning of RT was 69 years (range 50-86ys). Median PSA before RT was 1.2 ng/mL (range 0.0-6.2ng/ml). Concomitant androgen deprivation therapy (ADT) was applied to 32 patients, median duration of neoadjuvant ADT before start of RT was 2.8 mo (range 0.2-21.3mo). Median duration of adjuvant ADT was 14.8 mo (range 2.8-43.2mo). Median progression free survival (PFS) was 18.4 mo (range 2.7-46.6mo). Of 65 patients, 19 (29.2%) developed BCF caused by distant metastases in 12 (18.5%) patients, by local recurrences in four (6.2%) patients, of these two developed additional distant metastases. In three patients the cause of BCF is unknown due to missing imaging for restaging. Of the 19 patients with BCF, 10 patients were associated with prior or concomitant ADT to SRT. Conclusion The integration of 68 Ga-PSMA PET imaging in RT planning and consecutive dose escalation RT led to a satisfying PSA-PFS of 65% in the high-risk PC patient group. With a median follow-up of 20.3 mo, PFS was mainly limited due to a high distant failure rate implying the need for intensified systemic treatment in a subset of patients. Treatment-related toxicity on gastrointestinal and genitourinary tract will be evaluated. EP-1597 Dose-escalation for early salvage radio- therapy in prostate cancer improves bDFS E. Latacz 1 , P. Dirix 1 , B. De Laere 2 , P. Van Dam 2 , P. Meijnders 1 , P. Huget 1 , D. Verellen 1 1 Department of Radiation Oncology- Iridium Cancer Network- Oncology Center GZA Hospitals Sint-Augustinus, Radiation Oncology, Wilrijk, Belgium 2 Translational Cancer Research Unit- Oncology Center GZA Hospitals Sint-Augustinus, Translational Cancer Research Unit, Wilrijk, Belgium Purpose or Objective To compare a dose of 66.0 vs 70.0 Gy to the prostate bed in patients referred for early salvage radiotherapy (SRT) after radical prostatectomy. Material and Methods From January 2009 until December 2015, 159 patients with a biochemical recurrence after radical prosta- tectomy were referred for early SRT (PSA <0.5 ng/ml). Median time between surgery and SRT was 29 months (range 6-161m). Mean PSA at time of referral was 0.2 ng/ml (range 0.02-4.9 ng/ml). Until August 2014, a dose of 66 Gy in 33 fractions was delivered to the prostate bed. Thereafter, a dose of 70 Gy in 35 fractions was applied. All patients were treated with intensity- modulated radiotherapy with identical simulation and image-guidance protocols. No concomitant androgen- deprivation therapy was used. In 51 (32%) patients, some elective nodal irradiation (ENI) was performed, generally only covering a limited field including the bilateral

obturator, internal and external iliac nodes up to the lower border of the sacro-iliacal joint. A biochemical relapse after SRT was defined as a PSA level that had increased to ≥ 0.2 ng/mL from the post-SRT nadir confirmed by one more consecutive result at least 2 weeks later. The time to biochemical relapse after SRT was defined as the period from the end of SRT to the confirmatory PSA measurement. The close-out date for survival analysis was June, 2017. Acute and late gastro- intestinal (GI) and genito-urinary (GU) toxicities were scored according to CTCAE v4.0. Results

Hundred patients received 66.0 Gy to the prostate bed and 59 patients received 70.0 Gy. Patient demographics were comparable between both groups ( Table 1 ). Mean follow-up was 28 months (range 3-67m). At 2-years of follow-up, biochemical disease-free survival (bDFS) was 78% and 86% for patients treated with 66 Gy and 70 Gy, respectively (p = 0.04, Figure 1 ). Univariate analysis showed a better bDFS in patients treated with a higher dose to the prostate bed (p = 0.04) and a lower Gleason score (p= 0.05). There was no statistically significant correlation between bDFS and pT-stage, pN-stage, PSA at time of referral (<0.2 vs. > 0.2 ng/ml), nor ENI. In multivariate analysis, a higher dose to the prostate bed (HR 0.32, 95%CI 0.12-0.86, p=0.02) and a lower Gleason score (HR 0.15, 95%CI 0.03-0.72, p = 0.02), remained significant. Acute toxicity was available for all patients, there were no grade 4/5 toxicities in either group. The differences between the 2 groups were not significant on a chi-square test regarding both GI (p = 0.98) and GU (p = 0.61) toxicities. Late toxicity was available for 148 patients, there were no grade 4/5 toxicities in either group. The differences between the 2 groups were not significant regarding both GI (p = 0.98) and GU (p = 0.57) toxicities.