Abstract Book

S859

ESTRO 37

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. radiotherapy 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 prostatectomy 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 EP-1597 Dose-escalation for early salvage

and increasing number of patients are necessary to adequately evaluate actual significance of these differences on clinical outcomes

EP-1596 Follow-up of prostate cancer patients receiving 68Ga-PSMA-PET guided dose escalation radiotherapy L. Pfetsch 1 , K. Schiller 1 , M. Devecka 1 , T. Maurer 2 , M. Eiber 3 , S. Combs 1 , G. Habl 1 1 Technical University of Munich, Department of Radiation Oncology, Munich, Germany 2 Technical University of Munich, Department of Urology, Munich, Germany 3 Technical University of Munich, Department of Nuclear Medicine, Munich, Germany Purpose or Objective To determine the influence of 68 Ga-Prostate Specific Membrane Antigen (PSMA) PET imaging on survival outcome and toxicity rates in prostate cancer (PC) patients after consecutive high-dose radiotherapy (RT) in a primary setting as well as for local recurrence or for lymph node (LN) metastases. 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