ESTRO 36 Abstract Book

S380 ESTRO 36 _______________________________________________________________________________________________

to late toxicity, there is no significantly difference in late GI (RR=1.04, 95%CI: 0.88-1.23, p =0.63) and GU toxicity (RR=1.10, 95% CI: 0.47- 2.40, p =0.26) at 5-years. Since severe heterogeneity were existed, we also divided these studies into dose-escalated and no dose-escalate H-RT group. Dose-escalated H-RT increased in late GI toxicity (RR=1.80, 95%CI: 1.32-2.43, p =0.0002) and GU toxicity (RR=1.38, 95%CI: 1.07-1.79, p =0.01) significantly, while no dose-escalated H-RT did not (GI: RR=0.82, 95%CI: 0.68- 1.00, p =0.05; GU: RR=0.92, 95%CI: 0.72-1.16, p =0.46). Conclusion This meta-analysis provides more reliable evidence that H- RT decreased biochemical failure rate, while did not improve overall survival. For dose-escalated H-RT also decreased BCDF rates, and accordingly increased late GI and GU toxicity, while for those without dose-escalated H- RT, there is no difference in BCDF and late GI and GU toxicity. PO-0725 Sigmoid colon is an important organ at risk for high-grade faecal urgency after pelvic radiotherapy R. Jadon 1 , P. Parsons 2 , L. Hanna 1 , M. Evans 1 , J. Staffurth 1 1 Velindre Cancer Centre, Department of Clinical Oncology, Cardiff, United Kingdom 2 Velindre Cancer Centre, Department of Medical Physics, Cardiff, United Kingdom Purpose or Objective Faecal urgency is a common symptom after pelvic radiotherapy negatively impacting quality of life for survivors of pelvic malignancies. Compared with other symptoms such as rectal bleeding and incontinence, dose- volume predictors of faecal urgency are not well established and have not been discussed in the QUANTEC reviews. In this study dose-volume predictors of faecal urgency and constraints to potentially prevent it are sought. Material and Methods Patient-reported late bowel toxicity data was collected for patients treated with pelvic radiotherapy 12 months post-treatment using the subjective LENT-SOMA patient questionnaire. Treatment plans for these patients were retrospectively analysed with contouring of potential organs at risk including bowel loops, bowel bag, small bowel, large bowel, sigmoid, rectum and anal canal. Dose-volume predictors for these organs were sought using multivariate logistic regression analysis, with a p-value of <0.05 considered significant. Constraints from these significant dose-volume predictors were then determined to dichotomise patients into those with and without faecal urgency. Chi-squared analysis was used to assess the 'goodness of fit” of these constraints. The constraints were re-explored on the 24 months post-treatment toxicity data for the same patients. Results 203 patients returned questionnaires including 128 prostate and pelvic node patients, 19 bladder patients, 38 endometrium and 18 cervical cancer patients. 73% were treated with conformal radiotherapy and 27% with IMRT/ VMAT. Faecal urgency was reported by 52% of patients, with 41% reporting high grade (grade 3-4 toxicity), defined as 'daily” (grade 3) or 'constantly” (grade 4). There was no clear difference in urgency rates by diagnosis or radiotherapy technique used. Dose volume parameters of bowel loops, large bowel and sigmoid were predictive of faecal urgency. However only sigmoid parameters (V10, V15, V25) could be used to derive statistically significant constraints below which toxicity would be clinically acceptable. These constraints are detailed in the table below. At 24 months these constraints still demonstrated the ability to dichotomise patients with and without toxicity, although not statistically significantly.

Conclusion These results suggest sigmoid colon to be a responsible OAR for faecal urgency, and reduction of sigmoid dose may improve faecal urgency rates for pelvic radiotherapy patients. Further validation of the constraints derived in an independent sample of patients is required. PO-0726 Dose escalation with HDR brachytherapy for intermediate- and high-risk prostate cancer R. Chicas-Sett 1,2,3 , F. Celada 1 , J. Burgos 1 , D. Farga 1 , M. Perez-Calatayud 1 , S. Roldan 1 , E. Collado 1 , B. Ibañez 1 , J. Perez-Calatayud 1 , A. Tormo 1 1 La Fe Polytechnic and University Hospital, Radiation Oncology, Valencia, Spain 2 Universidad Católica de Valencia "San Vicente Mártir", Escuela de Doctorado, Valencia, Spain 3 Recoletas Oncology Institute- Campo Grande Hospital, Radiation Oncology, Valladolid, Spain Purpose or Objective Dose escalation by the combined therapy between high- dose-rate brachytherapy (HDRB) plus external beam radiation therapy (EBRT) has reported excellent clinical results, strongly supporting its use in high-risk patients. We present our experience of dose escalation using a single-fraction HDRB for intermediate- and high-risk prostate cancer. Material and Methods From August 2010 to September 2015, 332 patients with National Comprehensive Cancer Network intermediate- (n=59) and high-risk (n=273) prostate cancer were evaluated. Median age was 71 years (range 46-84). The staging was performed via magnetic resonance imaging (MRI) in every case, as is showed in table1. Patients underwent a single-fraction HDRB boost of 15 Gy (n=242) or 9-9.5 Gy (n=90) if seminal vesicles were infiltrated using real-time TRUS based planning. Four gold fiducials markers were implanted immediately after HDRB. EBRT 46 Gy/23fx or 60 Gy/30fx was performed 4 weeks after HDRB to patients who received 15 Gy and 9-9.5 Gy HDRB boost respectively. All patients received EBRT by Volumetric Arc Therapy (VMAT) with imaging guided by CBCT. A total of 148 patients (45%) received a dose of 46 Gy to the pelvis according to the risk pelvic node involvement by ROACH formula. The constraints recommended by GEC/ESTRO have been respected in all brachytherapy plans (Rectum D 2cc ≤ 75Gy; urethra D10 ≤120 Gy EQD 2 ). GI and GU toxicities were reported according to CTAE v4.0. In all, 290 patients (87%) received neo-concomitant and adjuvant androgen deprivation therapy. Patients were followed prospectively and the Phoenix definition was used to assess biochemical failure