ESTRO 38 Abstract book

S839 ESTRO 38

moderate hypofractionated external beam radiotherapy (RT) for prostate cancer delivered either twice or thrice a week. Material and Methods From 2003 to 2017, 157 patients with localized prostate cancer and an estimated risk of nodal metastases of ≤20% were treated consecutively on the prostate ± seminal vesicles with 56 Gy in 4 Gy-fractions delivered either twice (86 patients, from 2003 to 2010, group-1) or thrice (71 patients, from 2010 to 2017, group-2) a week using IMRT or VMAT techniques. Median OTT for group-1 and group-2 were 46 (range, 38-90) and 30 (range, 29 to 40) days, respectively. Sixty-one patients (39%) received, in addition, neoadjuvant and concomitant androgen deprivation (median duration of 6 months). Gastrointestinal (GI) and genitourinary (GU) toxicities were scored according to the Common Terminology Criteria for Adverse Events version 3.0 grading scale. Biochemical relapse-free survival (bRFS) was assessed using the Phoenix definition. The median follow-up time was 110 and 56 months for group 1 and 2, respectively. Results At 6 weeks, patients treated thrice-a-week experienced higher acute ≥ grade-2 GU toxicity compared to those treated twice-a-week (25.4% vs 5.8%, p=0.001) even though none presented ≥ grade-3 GU or GI toxicity in the thrice-a-week group. Although, 5-year ≥ grade-2 late GU toxicity-free survival was higher in group-1 (95.9%±2.3%) than in group-2 (81.5±4.9%, p=0.003), the long range GU toxicity was not different between both groups. Furthermore, no differences in ≥ grade-2 late GI toxicity- free survival were observed between both groups (97.5±1.7% vs. 97±2.1% for groups1 and 2, respectively). The 5-year bRFS was not different for patients treated twice compared to those treated thrice-a-week (80.6±4.5% vs. 85.3±4.8%, respectively p=0.441), as much as for patients treated in >5 weeks vs. those treated in ≤ 5 weeks (81.3±4.4% vs. 84.4±5.1%, respectively p=0.584). Conclusion Less vs. more than 5 weeks OTT may increase acute and late GU side effects without significantly improving bRFS in patients treated to high effective doses (>80 Gy) with moderate hypofractionated RT for prostate cancer. However, the similar prevalence of side effects in the long range for both groups of patients may favor that patients find more convenient to be treated in 5 rather than 7 weeks. The role of OTT on long-term outcome and toxicity of prostate cancer patients treated with hypofractionation deserves further prospective evaluation. EP-1555 Precision of deformable image registration for high-field MR-Linac treatment of prostate cancer R.L. Christiansen 1,2 , L. Dysager 3 , O. Hansen 2,3 , C. Brink 1,2 , B. Uffe 1,2 1 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark ; 2 University of Southern Denmark, Department of Clinical Research, Odense, Denmark ; 3 Odense University Hospital, Department of Oncology, Odense, Denmark Purpose or Objective Online radiotherapy (RT) plan adaption requires re- delineation of target and organs at risk (OAR), while the patient is on the treatment couch. Automated deformable image registration (DIR) resulting in deformation of the planned target and OAR delineations will potentially minimize time spent on re-planning if deformation of these structures is sufficiently accurate for clinical use. This study investigates the compares the precision of automatically deformed structures with manually defined structures in high-risk prostate cancer patients. Material and Methods The study includes six high-risk prostate patients referred for curative RT and prescribed 78 Gy to the prostate and the proximal 2 cm of the seminal vesicles (SV) and 56 Gy

better outcomes than surgical patients. Here we report the results of our experience with high-dose hypofractionated helical Image Guided-Intensity Modulated Radiotherapy (IG-IMR) (Tomotherapy, Accuray, Wisconsin) in high-risk prostate cancer (HR PCa) patients (pts). Material and Methods One hundred thirty-three HR PCa pts treated with hypofractionated helical IG-IMRT from April 2006 to July 2015 were included in this analysis. HR PCa was defined as the presence of one or more of the following characteristics: Gleason Score ≥ 8, and/or initial PSA ≥ 20 ng/ml, and/or clinical stage ≥ T3b. Seventeen pts had radiologically positive nodes (N1). The median age of the patients was 75 (range: 57-90) years. They were treated on pelvic lymph nodes (including common iliac chain) to a total dose of 51.8 Gy, with simultaneous integrated boost (SIB) on prostate and seminal vesicles to 74.2 Gy in 28 fractions, delivered in 5 ½ weeks. The 2 Gy equivalent dose, considering the accepted a/b ratio of 1.5 for prostate cancer, is 88 Gy. Androgen deprivation therapy (ADT) was prescribed to 121/133 pts for a median of 38 (0- 120) months (pts with biochemical failure during ADT continued the hormonal treatment). In N0 pts ADT was prescribed for median of 32 months. Median initial PSA was 16 (1.41-826.00) ng/mL. Results With a median follow up of 60 (11.8-145.2) months, biochemical relapse free survival (bRFS) was 79.7% and distant metastasis free survival (DMFS) was 86.5%. Overall survival was 69.2%, and cancer specific survival (CSS) was 91.7%. Important differences were registered between N0 and N1 pts (see Table 1). Gastro-Enteric (GE) acute grading (G) ≥ 2 toxicity was 6 %, G3 only 0.8%. Genito- Urinary (GU) acute G≥2 toxicity was 30.1%, G3 only 0.8%. Late toxicity was as follows: GE≥ G2 12.8%, G3 3%; GU≥ G2 21.1%, G3 9%, but with spontaneous or therapeutic resolution, thus only 3.8% of pts presented G3 GU toxicity at the last follow up. Conclusion Our results confirm that high-risk prostate cancer patients, most of them not suitable for surgery due to comorbidities, irradiated on pelvic lymph nodes with dose- escalation on prostate, associated to androgen deprivation, obtain good 5-year biochemical control, with acceptable acute and late toxicity. Positive lymph nodes pts present worse outcomes. EP-1554 Twice vs thrice-weekly moderate hypofractionated EBRT for PCa: does overall treatment time matter? V. Achard 1 , S. Jorcano 2 , M. Rouzaud 1 , L. Escude 2 , R. Miralbell 1 , T. Zilli 1 1 Hopitaux Universitaires Geneve, Radio-oncology, Geneva, Switzerland ; 2 Teknon Oncologic Institute, Radiation Oncology, Barcelona, Spain Purpose or Objective For prostate cancer the influence of overall treatment time (OTT) remains a controversial issue. Although a protracted OTT may have a detrimental effect on long- term disease control with standard fractionation, its impact on outcome has never been explored in moderate hypofractionation. Furthermore, changes in dose per fraction and OTT can impact tolerance and treatment- related side-effects. This study is aiming to evaluate the influence of OTT in disease control, acute, and long-term side effects with Patients bRFS DMFS CSS High Risk, N0 82.8% 89.7% 94.8% N1 52.9% 58.8% 70.6%