Abstract Book

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Results Median follow-up was 5 years. Actuarial 5-year biochemical DFS was 93.4%; including 100% for LR and 88.8% for IR patients. Cumulative incidence of late grade 3 or higher toxicity was 2.3% (1.9% grade 3 and 0.4% grade 4), yielding an upper 95% confidence interval of 4.4%. Grade 3 or higher toxicity was limited to the GU domain, with a 0% incidence in the GI domain. Grade 2 GI toxicity was seen in 9/259 patients (3.4%), of which 2/259 (0.8%) was due to rectal bleeding. As seen in the table, the overall urinary and bowel scores declined at month 1 and 12 after treatment; the overall urinary domain score fluctuating thereafter, with recovery at 5 years. Urinary EPIC subset evaluation as tabulated below revealed a persistent decrease in the incontinence score at 24 months and beyond, with irritative/obstructive scores returning to baseline after 12 months. The bowel score returned to baseline after 12 months. The hormonal score did not change at any time. The EPIC sexual score, which began at an already impaired baseline level of 55.9, decreased by a nonsignificant degree within the first month and to a clinically significant degree by >= 4 years out, at least some of which could be due to normal aging in a senior population. Conclusion Heterogeneous 'HDR-like” prostate SBRT appears to be safe and effective at median follow-up of 5 years in this prospective trial, compared to published results of other existing treatment modalities including surgery, IMRT, and brachytherapy. OC-0505 Interim results of a randomized trial of observation versus SABR for oligometastatic prostate cancer P. Tran 1 , N. Radwan 1 , R. Phillips 1 , A. Ross 2 , S. Rowe 3 , M. Gorin 2 , E. Antonarakis 4 , C. DeVille 1 , S. Greco 1 , S. Denmeade 4 , C. Paller 4 , D. Song 1 , M. Diehn 5 , H. Wang 4 , M. Carducci 4 , K. Pienta 2 , M. Pomper 3 , T. DeWeese 1 , A. Dicker 6 , M. Eisenberger 4 1 Johns Hopkins University The Sidney Kimmel Comprehensive Cancer Center, Department of Radiation Oncology, Baltimore, USA 2 Johns Hopkins University, Department of Urology, Baltimore, USA 3 Johns Hopkins University, Department of Radiology, Baltimore, USA 4 Johns Hopkins University The Sidney Kimmel Comprehensive Cancer Center, Department of Oncology, Baltimore, USA 5 Stanford University, Department of Radiation Oncology, Stanford, USA 6 Thomas Jefferson University, Department of Radiation Oncology, Baltimore, USA Purpose or Objective Local ablative treatment to oligometastatic patients can result in long term disease-free survival in colorectal and sarcoma patients. The importance of consolidating all macroscopic tumor deposits in prostate cancer in the modern era is an unanswered question. Stereotactic ablative radiation (SABR) is highly focused, high-dose radiation that is ideally suited for treatment of

oligometastatic patients. There are also exciting animal and patient studies suggesting that SABR can activate the immune system against cancer cells. Here we report on interim safety, clinical and translational outcomes of our Phase II randomized trial of SABR to men with recurrent low volume (1-3 metastases) hormone sensitive metastatic prostate cancer. Material and Methods Patients are randomized 2:1 to SABR:observation with minimization to balance assignment by primary intervention, prior hormonal therapy, and PSA doubling time. Progression after 6 months will be compared using Fisher's exact test. Hazard ratios and Kaplan-Meier estimates of progression free survival (PFS), ADT free survival (ADT-FS), time to locoregional progression (TTLP) and time to distant progression (TTDP) will be calculated based on an intention-to-treat. Local control will be assessed using RECIST 1.1 criteria. Adverse events will be summarized by type and grade. Quality of life pre- and post- SABR will be measured by Brief Pain Inventory. Further fundamental analysis of the oligometastatic state with be achieved through correlation with germline DNA repair gene mutations using the Color Genomics panel, investigational 18 F-DCFPyL PET/CT imaging and measurement of circulating tumor cells, circulating tumor DNA and deep sequencing of circulating T-cell receptor repertoires. Results Since activation in April 2016 we have had enrollment of 37 men and subsequent randomization of 36 out of the target 54. Thus far, as expected only minimal side-effects (no >Grade 3 toxicity) have been observed from the SABR alone. 67% (6/9) of eligible men on the observation arm have progressed at 6-months versus 33% (5/15) for the SABR arm. 2/20 (10%) men tested had germline DNA repair gene mutations (MUTYH c.1187G>A & CHEK2 c1555C>T). CellSearch™ detected only 1 CTC/7.5-ml in two men and the remaining eight men had no CTCs (20% detectability). In contrast, 9/17 (53% detectability) men had detectable CTCs using the HD-CTC platform and 3/4 (75%) interpretable cases showed a response following SABR. Other radiologic and blood correlatives are pending analysis and will be presented. Conclusion The ORIOLE trial (NCT02680587) is the first randomized Phase II study in the Western Hemisphere evaluating the safety and efficacy of SABR in oligometastatic hormone- sensitive prostate cancer. Preliminary clinical data is promising and leading-edge laboratory and imaging correlates will allow an unprecedented opportunity to characterize, in isolation, the effects of SABR on the dynamics of and immunologic response of the oligometastatic state. OC-0506 A model of tumour response to radiation considering 3D vascular architectures and vascular damage A. Gago-Arias 1 , I. Espinoza 1 , P. Franco 2 1 Pontificia Universidad Católica de Chile, Instituto de Física, Santiago, Chile 2 Pontificia Universidad Católica de Chile, Instituto de Física y Centro de Imágenes Biomédicas- Departamento de Ingeniería Eléctrica, Santiago, Chile Purpose or Objective It is well known that the tumour oxygenation status, which depends on the tumour microvasculature, affects tumour cells radiosensitivity. Additionally, high radiation doses (> 8–10 Gy) have been observed to induce severe Proffered Papers: PH 9: Analysis of treatment outcomes