ESTRO 36 Abstract Book

S704 ESTRO 36 2017 _______________________________________________________________________________________________

Y. Van Wijk 1 , B. Vanneste 2 , S. Walsh 2 , S. Van der Meer 3 , B. Ramaekers 4 , W. Van Elmpt 2 , M. Pinkawa 5 , P. Lambin 2 1 Maastricht university, School for Oncology and Developmental Biology, Maastricht, The Netherlands 2 MAASTRO clinic, Radio Oncology, Maastricht, The Netherlands 3 Adelante Zorggroep, Audiology, Maastricht, The Netherlands 4 Maastricht university, Heath Economics, Maastricht, The Netherlands 5 University Hospital Aachen, Michael Pinkawa, Aachen, Germany Purpose or Objective Dose escalation during external beam radiation in prostate cancer patients has been shown to improve progression free survival, but also leads to increased risk of gastro- intestinal (GI) toxicity due to high radiation dose in the rectal wall. A method to reduce this dose is implantation of an implantable rectum spacer (IRS) to increase the distance between the rectal wall and the high dose region. Two commercial systems exist: hydrogel spacer (SPA) and Rectal balloon implant (RBI). In this study, a virtual IRS was developed to help identify the patients for whom it is cost-effective to implant an IRS. The research goal was to test whether this virtual IRS is a viable tool to tailor the decision of an IRS implantation to be beneficial for the specified patient. Material and Methods A virtual IRS was developed using a model based on scans of 11 patients with a RBI. This model was used to create a deformation field (i.e. virtual IRS) that was applied to scans of patients without an IRS. To test the virtual IRS, scans were used of 16 patients before and after the implantation of an IRS: 8 with a RBI, and 8 with a SPA. The real IRS scans were compared to scans with a virtual IRS. IMRT plans were made based on scans before the IRS, after IRS and with the virtual IRS, prescribing 78 Gy to the target volume. These plans were used to compare the rectum dose, the Normal Tissue Complication Probability (NTCP) for GI and the related cost-effectiveness of no IRS compared with the virtual IRS and the real IRS. The NTCP model used previously validated dosimetric parameters for late rectal bleeding: mean dose (Gy) and V75 (%) as dosimetric predictors for late rectal bleeding. It also included clinical parameters such as haemorrhoids or use of hormonal therapy. The cost-effectiveness was analyzed using an earlier published Markov model. The incremental net monetary benefits (iNMB) was calculated (assuming a willingness to pay of €80.000/QALY). Results The NTCP for the patients with a RBI and the virtual IRS were 4.1% [range: 3.6-5.0%], and 4.0% [range: 3.4%-5.3%] respectively. For the patients with a SPA the mean NTCP was 4.6% [range: 3.7%-6.1%] while this was 4.4% [range: 3.8%-4.7%] for the virtual IRS (Table 1).

experienced a biochemical recurrence with the 2-year biochemical recurrence-free survival (bRFS) being 91%. A persistant PSA ≥ 0.5 ng/ml after RP was significantly associated with decreased bRFS (p=0.028). Conclusion Risk adapted dose intensified postoperative RT is feasible and associated with favorable acute and late GU and GI toxicity rates and promising bRFS rates. EP-1326 Long term patients clinical outcome after salvage post-prostatectomy Radiation Therapy (RT) P. Pietro gabriele 1 , E. Elisabetta garibaldi 2 , A. Angelo maggio 3 , e. Elena delmastro 4 , a. Andrea galla 4 , s. Sara bresciani 5 , D. Domenico Gabriele 6 , M. Michele Stasi 5 1 irccs-fpo candiolo cancer center, radiotherapy pedartment, candiolo turin, italy 2 irccs-fpo candiolo cancer cenetr, radiotherapy department, candiolo turin, italy 3 irccs-fpo candiolo cancer institute, medical physics, candiolo turin, italy 4 irccs-fpo candiolo cancer center, radiotherapy department, candiolo turin, italy 5 irccs-fpo candiolo cancer center, medical physics, candiolo turin, italy 6 sassari university, radiotherapy department, sassari, italy Purpose or Objective To study the outcome of patients treated for prostate cancer with salvage radiotherapy after radical surgery. Material and Methods From January 2000 to December 2015 we treated for salvage in our Institution 234 patients (44-75 ys, median 64) affected by prostate cancer operated and with biochemical/clinical recurrences. The pre surgery PSA was 9 (0.36-90) ng/mL, pathologic GS 7 (4-9) and cT1, 2, 3 and 4 were 1, 61, 137 and 1, respectively. Lymph node invasion was presented in 11 patients; the number of nodes removed was 6 (0-40) and positive margins were 64 (27 %); post-surgery PSA was 0.10 (0-2). Radiation therapy was performed with Linac from 1999 to 2009 by 3DCRT and with Tomotherapy from 2010 by IMRT-IGRT. Radiation dose were 70.2 Gy (61.6-79.2) to the prostate bed and 54 Gy (45-57.6) to the pelvis, 1.8 Gy per fraction; the pelvis was irradiated in 46 patients (20%). 66 patients (28%) were treated during RT with hormone therapy (HT). The median time from surgery to RT was 40.7 months (range: With a median FU of 117 months (17.6-303) the 10 years prostate Cancer Specific Survival was 88%; Clinical Relapse Free Survival was 67 % and Biochemical Relapse Free Survival only 36%. Cox univariate and multivariate analysis were performed and the results are the following: in multivariate analysis for Cancer Specific Survival are predictive PSA pre RT (p=0.0018; HR=1.18), PSA measured at last follow-up (p=0.0018; HR=1.04) and nodal invasion (p=0.024; HR=5.9); for Biochemical Free Survival are predictive D’Amico classification (p=0.002; HR=1.6) and cT(p=0.007; HR=1.7); for Clinical Relapse Free Survival GS(p=0.0008; HR=1.7) and last follw-up PSA(p=0.0001; HR=1.02). Conclusion In this, based on a large database, it was found that the PSA measured at last low-up was predictor of Prostate Cancer Specific and Clinical Relapse free survival while GS and D’Amico Classification were significantly independent prognostic factors of clinical relapse and Biochemical Free Survival for patients treated with postprostatectomy salvage RT. Acknowledgments: This work was supported by “5 per Mille 2009 MinisteroSalute-FPRC Onlus”. EP-1327 Decision Support System to implant a rectum spacer during prostate cancer radiotherapy 6-212). Results

The mean iNMB of the RBI was -€ 1062 [range: -€ 1,974-€ 658]. For the virtual IRS in these patients this was -€ 1042 [range: -€ 1,526.8-€ 400]. The mean iNMB of the SPA was -€ 605 [range: -€ 2,383-€ 427]. For the virtual IRS this was