ESTRO 36 Abstract Book

S291 ESTRO 36 2017 _______________________________________________________________________________________________

needed to study the impact of the combination on overall survival and PFS. PV-0551 PSMA PET/CT vs MRI for GTV delineation in prostate cancer: a comparison with histology C. Zamboglou 1 , V. Drendel 2 , C.A. Jilg 3 , H.C. Rischke 1 , B. Teresa I. 4 , T. Krauss 5 , M. Werner 2 , M. Bock 6 , M. Langer 5 , P.T. Meyer 4 , A.L. Grosu 1 1 Medical Center - University of Freiburg, Department of Radiation Oncology, Freiburg, Germany 2 Medical Center - University of Freiburg, Department of Pathology, Freiburg, Germany 3 Medical Center - University of Freiburg, Department of Urology, Freiburg, Germany 4 Medical Center - University of Freiburg, Department of Nuclear Medicine, Freiburg, Germany 5 Medical Center - University of Freiburg, Department of Radiology, Freiburg, Germany 6 Medical Center - University of Freiburg, Department of Radiology- Medical Physics Division, Freiburg, Germany Purpose or Objective The exact delineation of the intraprostatic tumour burden is crucial for treatment planning in primary prostate cancer (PCa). We compared 68 Ga-HBED-CC-PSMA PET/CT with multiparametric MRI (mpMRI) for gross tumour delineation in patients with primary PCa based on slice by slice correlation with histopathological reference material. Material and Methods Patients with histopathologically proven primary PCa underwent 68 Ga-HBED-CC-PSMA PET/CT (n=10) and MRI (n=7) followed by radical prostatectomy. Resected prostates were scanned by ex-vivo CT using a special localizer and prepared for histopathology in a customized cutting device. Invasive PCa was delineated on a HE stained histologic tissue slide and matched to ex-vivo CT to obtain gross tumor volume (GTV-)histo. Ex-vivo CT including GTV-histo and MRI data were matched to in-vivo CT(PET). Consensus contours based on MRI (GTV-MRI), PSMA PET (GTV-PET) or the combination of both (GTV- union/-intersection) were delineated. In each in-vivo CT slice the prostate was separated into 4 equal segments (total 340 segements) and sensitivity and specificity for PSMA PET and mpMRI were assessed by comparison with histological reference material. Furthermore, the spatial overlap with GTV-histo was measured. In the case of multifocal PCa (4/7 patients), SUV values (PSMA PET) and b-values (diffusion weighted MRI) were obtained for each lesion. Results GTV-histo was detected in 225 of 340 segments (66%). Sensitivity and specificity for GTV-PET, GTV-MRI, GTV- union and GTV-intersection were 75% and 87%, 70% and 82%, 82% and 67%, 55% and 99%, respectively. GTV-histo had on average the highest overlap with GTV-union (57±22%), which was significantly higher than overlap with GTV-MRI (p=0.016) and GTV-PET (p=0.016), respectively. In every patient with multifocal PCa there was one lesion which had both the highest SUV and the highest b-value (mean and max), which was always the largest lesion in histology. Conclusion 68 Ga-HBED-CC-PSMA PET/CT and mpMRI showed high sensitivity and specificity in detection of primary PCa. The combination of both methods performed even better in terms of sensitivity (GTV-union) and specificity (GTV- intersection). A good spatial overlap with GTV-histo was observed for PSMA PET/CT and mpMRI alone which was significantly improved by GTV-union. Further studies are warranted to analyse the impact of these preliminary findings for therapeutic (focal therapy) strategies in primary PCa.

PV-0552 Urethra-sparing SBRT for prostate cancer: acute toxicity results from a randomized phase II trial T. Zilli 1 , S. Jorcano 2 , S. Bral 3 , C. Rubio 4 , A. Bruynzeel 5 , A. Oliveira 6 , U. Abacioglu 7 , H. Minn 8 , Z. Symon 9 , R. Miralbell 1,2 1 Hôpitaux Universitaires de Genève, Radiation Oncology, Geneva, Switzerland 2 Teknon Oncologic Institute, Radiation Oncology, Barcelona, Spain 3 Onze-Lieve-Vrouwziekenhuis, Radiation Oncology, Aalst, Belgium 4 Hospital Universitario Sanchinarro, Radiation Oncology, Madrid, Spain 5 VU University Medical Center, Radiation-Oncology, Amsterdam, The Netherlands 6 Portuguese Institut of Oncology, Radiation Oncology, Porto, Portugal 7 Neolife Medical Center, Radiation Oncology, Istanbul, Turkey 8 University Hospital Turku, Radiation Oncology, Turku, Finland 9 Sheba Medical Center, Radiation Oncology, Ramat Gan, Israel Purpose or Objective To present the acute toxicity results from a prospective multicenter phase II randomized trial of short or protracted urethra-sparing stereotactic body radiotherapy (SBRT) for localized prostate cancer (PCa). Material and Methods From 08/2012 to 12/2015, 170 patients (pts) from nine European centers with cT1c-3a N0 M0 PCa and a low risk of nodal involvement (≤20%, according to Roach et al.) were recruited and randomized according to two different overall treatment time (OTT) schedules: either 9 days (arm A, 84 pts), or 28 days, once-a-week, the same week- day (arm B, 86 pts). The prescribed dose was 36.25 Gy in 5 fractions of 7.25 Gy to the prostate ± seminal vesicles in both arms. The prostatic urethra, with a surrounding margin of 3 mm, received a lesser dose of 5 x 6.5 Gy = 32.5 Gy. All patients were treated either with a VMAT or IMRT technique under stereotactic conditions using Novalis linacs and ExacTrac image-guided technology. Genitourinary (GU) and gastrointestinal (GI) toxicity (CTCAE v4.0 grading scale), IPSS, and QoL scores (EORTC QLQ-PR25) were assessed at baseline, at the 5 th fraction (5fx), and 12 th weeks (12W) since SBRT start. Results 82 (median age 70 years) and 83 (median age 69 years) pts, respectively, from arms A and B, were retained for this analysis. Low-, intermediate-, and high-risk presentation was respectively 22%, 63%, and 15% (arm A) and 22%, 64%, and 14% (arm B). A 6-months androgen deprivation was used in 44% and 45% of the pts in arm A and B, respectively. The toxicity stopping rule of the study during the first 3-months was never activated. In both arms, Grade 1 GI toxicity increased from baseline to 5fx (from 19.5% to 38% and from 23% to 32% for arms A and B, respectively) returning back to baseline by W12 (18% for Arm A and 25% for Arm B). Only 2 cases of grade 2 GI toxicity (2.5%) were observed at 5fx in arm A. Grade 2 GU toxicity rates at baseline, 5fx, and W12 were 2%, 17%, and 11% vs. 5%, 19% and 6% in arms A and B, respectively (mainly moderate irritative and voiding symptoms). Only one grade 3 GU toxicity was observed at W12 in arm B (desobstructive TURP in a patient with a preexisting history of acute urinary retention). Median IPSS scores at the same endpoints were 6, 10, and 6 vs. 6, 10, and 7 for arms A and B, respectively, with similar IPSS-based QoL rates at baseline and W12 (80% of pts satisfied). No changes in EORTC QLQ-PR25 scores for GU, GI, and sexual domains were observed in both arms between baseline and W12.