ESTRO 38 Abstract book

S140 ESTRO 38

on pre-treatment mpMRI, the DIL was contoured with the use of 2 sequences (T2W and DWI). Contours were generated by consensus of two physicians. The site of local relapse was compared with the initial site of disease. The dose received by the site of recurrence was investigated. Results Forty-four percent of patients were low-risk and 56% intermediate-risk. The median prostate volume was 34cc (17-60). Median CTV and OAR doses were: V100: 96.5% (95- 99.4), V150 20.5% (13.7-35.1), V200 5.3% (3.1-10.1), Urethral Dmax 106% (103-111) and rectum 2cc 53 % (45- 48). The median follow-up period was 37 months (range 23-50). The PSA nadir was reached at 24 months follow-up, with a median value of 1.07 ng/mL. To date, 14 patients (32%) have experienced biochemical failure (4 patients low-risk and 10 intermediate-risk; p=0.013). Re-staging mpMRI showed local relapse in 12 patients (27.2%) and 11/12 patients underwent MRI-TRUS fusion biopsy confirming local relapse in 10 patients. The analysis of DVH of all 44 patients revealed that patients with biochemical failure had received significantly lower doses in terms of V100, V125 and D90 (p=0.032, p=0.018 and p=0.018 respectively). Of the 25 patients with DILs on diagnostic mpMRI, the mean D90 and D98 on DIL were lower for patients with biochemical failure (21.8 Gy and 20.1 Gy vs 22.2 Gy and 20.8 Gy, respectively; p=n.s). And in patients with confirmed local failure, the doses received by the index lesion were median D90=21.8 Gy (range 19.9 Gy-24.7 Gy) and median D98=20 Gy (19.9 Gy-22.5 Gy) Conclusion This dosimetric analysis demonstrates a dose-response relationship in patients treated with single fraction 19Gy. Patients with intermediate-risk disease, with visible DIL on mpMRI and patients treated with cooler implants have higher incidence of biochemical and local failure. The recurrence pattern is predominantly local in patients with initial gross disease on mpMRI. Patients in this study failed after receiving doses as high as D90=24.7Gy providing some rationale for further dose escalation to dominant intraprostatic nodules. OC-0284 Radiomic and dosimetric analysis of urethral strictures following prostate HDR monotherapy Y.M. Tsang 1 , D. Vignarajah 2 , A. Mcwilliam 3 , H. Tharmalingam 4 , A. Choudhury 3 , P. Hoskin 4,3 1 Mount Vernon Cancer Centre, Radiotherapy, Northwood Middlesex, United Kingdom ; 2 Sunshine Coast University Hospital, Clinical Oncology, Queensland, Australia ; 3 University of Manchester, Division of Cancer Sciences- School of Medical Sciences- Faculty of Biology Medicine and Health- Manchester Academic Health Sciences Centre, Manchester, United Kingdom ; 4 Mount Vernon Cancer Centre, Clinical Oncology, Northwood Middlesex, United Kingdom Purpose or Objective High dose-rate (HDR) brachytherapy as monotherapy is accepted as a safe and effective local treatment for organ-confined prostate cancer. However, urethral stricture has been reported as one specific late effect with HDR monotherapy with conflicting results in and rethral dose. Radiomics is an emerging field in the era of precision medicine and there is great potential with mining MRI radiomics to capture the intra-tumour heterogeneity of prostate cancer. Against this background, we have analysed a cohort of HDR monotherapy patients to establish the frequency of non- malignant urethral stricture and explore the relation between stricture formation and (i) dose distribution along the length of the urethra and (ii) MRI radiomic features of the prostate gland.

allowed. Patients on the 2 fractions arm had 2 dosimetries and fractions were delivered 6 hours apart. Toxicity was evaluated at 1, 3, 6 weeks and 3 months after treatment using Common Terminology Criteria for Adverse Events (CTCAE) score, IPSS and International Index of Erectile Function (IIEF-5), and compared to baseline. Descriptive statistics, t test, paired t test, Pearson Chi-Square and Fisher Exact test were used to describe and compare the groups. Statistical significance was 0.05 Results Median Follow-up is 16 (3- 33) months. Pre-treatment median prostate-specific antigen for arm1 and arm 2 were were 6.6±3and 6.7±2.7 respectively. T stages for arm 1 and arm2 were T1c = 55% and 57%, T2a = 31% and 31%, T2b = 9% and 12%, T2c 5% and 2 % respectively. Gleason score were mostly 7(3+4) 52% and 57%, 7(4+3) 28% and 30% respectively. Evaluation of sexual function showed the following values: with a mean base line of 13±6.8 and 15.2±6.5 compared to 12.9±6.8 and 12.2±6.4 at 12 weeks for arm1 and arm 2 respectives. IPSS categories at baseline were mild 6.3±4.4 and 6.7±4 for arm 1 and arm 2, respectively. At 1 week there was a small increase of the IPSS score 11.5±7.9 for arm 1 and 12.6±8.1 for arm 2. Patients start to recuperate at 3 weeks with IPSS being 8.4±5.7 vs 10±6.4 and returned to baseline at 3 months with 6.5±5.5 and 7.6±5.4 respectively. The most frequently symptoms at 3 weeks were urinary frequency and burning sensation. Most patients had Grade 0-1 acute urinary toxicity: 89.7 % or arm 1 and 90.4 % for arm 2. Urinary retention occurred in 6.7% of patients in arm 1 and 2.1% arm 2. There was a small increase in Grade 2 acute gastrointestinal toxicity 1% for arm 1 and 4.8% for arm 2. However, acute toxicity did not differ between arms (GU p=0.62, GI p= 0.47). Conclusion Both arms of the protocol either a single fraction of 19.5Gy or 2 fractions of 14.5Gy delivered in a one-day schedule are well tolerated. Acute GI and GU toxicities are the same in both arms during the first 12 weeks, erectile dysfunction seems to follow the same pattern. Further report with longer follow-up on toxicity will follow. OC-0283 Pattern of relapse and dosimetric analysis of a single dose 19Gy HDR-brachytherapy phase II trial A. Gomez-Iturriaga 1 , D. Buchser 2 , P. Minguez 3 , J.M. Espinosa 3 , F. Perez 3 , J. Cacicedo 2 , F. Suarez 2 , A. Gonzalez 2 , P. Bilbao 2 , F. Casquero 2 1 Hospital Universitario Cruces- Biocruces Health Research Institute, Radiation Oncology, Barakaldo, Spain ; 2 Hospital Universitario Cruces- Biocruces Health Research Institute, Radiation Oncology, Barakaldo- Bizkaia, Spain ; 3 Hospital Universitario Cruces- Biocruces Health Research Institute, Radiation Physics, Barakaldo- Bizkaia, Spain Purpose or Objective To report the pattern of relapse within the prostate with reference to the initial site of disease in patients treated with single fraction 19-Gy and to determine the dose delivered to these areas of recurrence to inform potential strategies of focused dose escalation. Material and Methods A total of 44 patients with low and intermediate-risk prostate cancer were treated according to an institutional review board-approved prospective study of single- fraction HDR brachytherapy. Treatment was delivered using 192 Ir to a dose of 19 Gy prescribed to the prostate, no margins were applied. Patients who experienced a biochemical failure underwent a re-staging multiparametric MRI(mpMRI) and MRI-TRUS fusion biopsy to rule-out local recurrence. Forty-two patients (95%) had a pre-treatment mpMRI. In patients with visible Dominant intraprostatic lesions (DIL)