ESTRO 36 Abstract Book

S718 ESTRO 36 2017 _______________________________________________________________________________________________

schedule: 24/58 (41%) patients with BR received 2.25 Gy in 32 fractions (Total dose:72 Gy); 34/58 (59%) patients with LR received 2.1 Gy in 33 fractions (Total dose: 69.3 Gy) to the prostate/seminal vesicle bed and 2.25 Gy in 33 fractions to the LR site (total dose:74.25 Gy) using a simultaneous integrated boost (SIB) technique; 6/58 (10%) patients received 1.6 Gy to the pelvic lymph nodes (total dose 52.8 Gy), using a SIB technique. Hormone therapy ( HT-LHRH analogue and/or anti-androgen) was administered to 17 patients (29%) with high risk features. Toxicity was graded according to the Common Terminology Criteria for Adverse Events version v4.0. Biochemical failure was defined by ASTRO criteria. The Kaplan-Meier method determined time-to-acute toxicity events and the Mann-Whitney test compared clinical and dosimetric variables in groups with and without acute toxicity. Results The median follow-up was 12 months (range:3-41).The median duration of HT was 85 months (range 2-168). Only G1-G2 acute genitourinary (GU) and intestinal (GI) toxicities occurred. Acute grade 1 GU toxicity occurred in 28 patients (48%), with 25 (43%) developing cystitis and 3 (5%) hematuria. Acute grade 2 GU toxicity (cystitis) developed in 6/58 (10%) patients, with 1 also affected by urinary retension (2%). Acute grade 1 GI toxicity (proctitis) occurred in 25/58 patients (43%), which was associated with rectal bleeding in 2 (3%). Acute grade 2 GI toxicity (proctitis) developed in 4/58 (7%) patients, which was associated with rectal bleeding in 1 (2%). Post Hypo-ART the median PSA was 0.1 ng/ml (range:0-7.01) and the nadir was 0.03 ng/ml (range: 0-5.67). Biochemical recurrence and /or loco-regional relapse occurred in 10/58 (17%) patients at a median of 19 months after treatment (range: 10-40). Statistical analysis: after Hypo- ART there was 50% probability of developing acute GU toxicity on day 52 and GI toxicity on day 43. Dmax to the prostate/seminal vesicle bed was greater in patients who developed acute GI toxicity. Conclusion Low grade acute GU and GI toxicity and early biochemical response demonstrated that moderate Hypo-SRT was safe and effective. A longer follow-up is required to confirm these outcomes. EP-1354 Delayed Salvage Radiotherapy for Macroscopic Local Recurrence after Radical Prostatectomy M. Shelan 1 , S. Odermatt 1 , B. Bojaxhiu 1 , O. Elicin 1 , D.M. Aebersold 1 , A. Dal Pra 1 1 Bern University Hospital, Radiation Oncology, Bern, Switzerland Purpose or Objective Salvage radiotherapy (SRT) is the only potentially curative therapy available for patients experiencing biochemical recurrence after radical prostatectomy (RP), and likely more effective when offered early at low PSA levels. This work aims to retrospectively assess clinical outcome and toxicity of patients treated with delayed SRT to radiologically and/or histologically proven macroscopic local recurrence. Material and Methods We report on a cohort of 56 patients with radiologically detected isolated macroscopic local recurrence on MRI and/or CT scan and treated with SRT between 2001 and 2015. Histological confirmation was available in 35 (63%) patients. A dose of 64-66 Gy (2 Gy/fr) was delivered to the prostatic bed followed by a dose escalation to 72-74 Gy (2 Gy/fr) to the site of macroscopic disease using image- guided IMRT (IG-IMRT). Patients were treated with concomitant short-course (6 months) of androgen deprivation therapy. Biochemical relapse-free survival (PSA nadir + 0.2 ng/ml; bRFS) and clinical relapse-free- survival (cRFS) were calculated using Kaplan-Meier

method. Baseline, acute and late urinary and gastrointestinal (GI) toxicity rates were reported using CTCAE v4. Results Median age at SRT was 71 years (57-81). Out of 56 patients, 9 (16%) had pT3b disease and 19 (34%) had positive surgical margins. Sixteen patients (29%) had Gleason score ≥ 8 at RP. The median time from RP to SRT was 58 months (5-172). Median pre-RT PSA was 2.8 ng/ml (0.2-29). At a median follow-up of 39 months (8-153) post- SRT, 20 patients (36%) had biochemical failure and 8 (14%) developed distant metastasis. Median time to BF after SRT was 30 months (13-116). The 3- and 5-year bRFS were 70.5% and 53,5%, respectively. The 3- and 5-year cRFS was 89.2% and 80%, respectively. High-risk patients (pT3b and/or Gleason score ≥ 8) had 3- and 5-year bRFS of 54% and 27%, while 3- and 5-year cRFS was 66.7% and 44.4%, respectively. Univariate and multivariate analyses showed that Gleason score ≥ 8 and perineural invasion were associated with lower bRFS (p=0.005 and 0.046, respectively). High-risk patients presented lower bRFS and cRFS when compared to lower risk patients (p= 0.03 and 0.001, respectively). At baseline, 4 patients (7%) had grade 3 urinary toxicity. Twelve patients (21%) developed grade ≥ 2 acute urinary toxicities. Three patients (5%) had grade 2 acute GI toxicities. No grade ≥ 3 acute GI toxicity occurred. Nine patients (16%) had grade ≥ 2 late urinary toxicities. No grade ≥ 2 late GI toxicity was reported. Conclusion Delayed SRT using dose escalated IG-IMRT to isolated macroscopic local recurrence is associated with poor oncological outcomes particularly in high risk patients (i.e. pT3b and/or Gleason score ≥ 8). Toxicity profile seems to be acceptable at a medium term follow up. Patients with high risk features should be strongly considered for earlier and intensified treatment approaches. EP-1355 Comparing toxicity in IMRT and particle therapy of prostate cancer in a ROCOCO in silico trial Y. Van Wijk 1 , E. Roelofs 2 , B. Vanneste 2 , S. Walsh 2 , P. Lambin 2 1 Maastricht university, School for Oncology and Developmental Biology, Maastricht, The Netherlands 2 MAASTRO clinic, Radio Oncology, Maastricht, The Netherlands Purpose or Objective Studies have shown that dose escalation has positive effect on tumour control probability when treating high risk prostate cancer. However, due to the higher dose in the rectum, the normal tissue complication probability (NTCP) for gastral intestinal (GI) toxicity is increased. The goal of this study is to investigate whether radiotherapy of high-risk prostate cancer with light-ion particles results in reduced NTCP when compared to IMRT. A comparison between doses and NTCP was made for three modalities: IMRT, proton therapy (IMPT) and carbon-ion therapy (IMIT)