ESTRO 36 Abstract Book

S62 ESTRO 36 _______________________________________________________________________________________________

Material and Methods This is a multicentric Rare Cancer Network (www.rarecancer.net) retrospective study launched in February 2016. Demographic, therapeutic and outcome data of 48 adult PS pts treated in 13 European and American Institutions were collected in a common database and then analysed. Median age was 64.5 years (range: 22 - 87). Curative surgery was delivered in 35 pts (prostatectomy = 19, cystoprostatectomy = 16), usually with lymphadenectomy (n = 24). Curative radiotherapy (RT) was delivered in 24 pts, as neoadjuvant (n = 2), postoperative (n = 17), or as definitive treatment (n = 5). Ten pts received neoadjuvant (n = 3) or adjuvant (n = 7) chemotherapy. None of the patients received hormonal therapy. Results Median follow-up was 67 months. Five-year local control (LC), overall survival (OS), cancer-specific survival, disease-free survival, and metastases-free survival rates were 48.9%, 45.2%, 52.4%, 29.7%, and 31.2%, respectively. Irradiated patients presented better 5-year LC (63.8% vs 38.8%, p = 0.2) but its impact was not confirmed in the 35 pts receiving curative surgery. In the subgroup of pT3-T4 patients treated with curative surgery, RT significantly improved the 5-year LC (45.7% vs 0%, p = 0.007) and OS (48% vs 0%, p = 0.014) rates. cT4 pts presented a significantly lower 5-year OS (60.1% vs 29.5%, p = 0.001) and LC (70.2% vs 11.4%, p < 0.001) rates. Histologic type did not significantly influence the LC and OS, but pts presenting a prostatic stromal sarcoma, a rhabdomyosarcoma, or a sarcomatoid carcinoma showed a trend toward a worse outcome (5-year LC [31.9% vs 59.2%] and OS [28% vs 70%]). Conclusion Adult PS has a bad prognosis. More advanced diseases present lower LC and OS rates. Curative RT should be considered part of the multidisciplinary approach to PS. PV-0131 MR-only prostate external radiotherapy treatment planning - a multi-center/multi-vendor validation E. Persson 1 , C. Gustafsson 1,2 , F. Nordström 3 , M. Sohlin 3 , A. Gunnlaugsson 4 , K. Petruson 5 , N. Rintelä 6 , K. Hed 6 , L. Blomqvist 7 , B. Zackrisson 7 , T. Nyholm 7,8 , L.E. Olsson 2 , C. Siversson 9 , J. Jonsson 7 1 Skåne University Hospital, Hematology- Oncology and Radiation Physics, Lund, Sweden 2 Lund University, Medical Physics, Malmö, Sweden 3 Sahlgrenska University Hospital, Medical Physics and Biomedical Engineering, Gothenburg, Sweden 4 Skåne University Hospital, Oncology, Lund, Sweden 5 Sahlgrenska University Hospital, Oncology, Gothenburg, Sweden 6 Karolinska University Hospital, Medical Radiation Physics and Nuclear Medicine, Stockholm, Sweden 7 Umeå University, Radiation Sciences, Umeå, Sweden 8 Uppsala University, Immunology- Genetics and Pathology, Uppsala, Sweden 9 Spectronic, Medical, Helsingborg, Sweden Purpose or Objective An important prerequisite for MRI only radiotherapy is the generation of a synthetic CT (sCT) from MRI-data. This study aims to validate the use of MriPlanner TM , a software for MR to sCT conversion, for 170 prostate cancer patients. Performed within the Swedish consortium Gentle Radiotherapy, this multi-center study enables a large- scale validation of calculated synthetic CTs for multiple vendors. This is a presentation of the full results of the MR-Only Prostate External RAdiotherapy (MR-OPERA) study. Poster Viewing : Session 3: Treatment planning

Material and Methods The four participating centers had MriPlanner TM (Spectronic Medical AB, Helsingborg, Sweden) installed as a cloud based service. The software makes use of an atlas- based generation method, called the statistical decomposition algorithm, which generates sCTs from T2- weighted MR-images. Study participation did not affect treatment prescription, and the patients followed the routine clinical workflow. A T2-weighted MRI, covering the external body contour, was added to the clinical MRI scan protocol. The MR-image was sent from the MR-scanner workstation to the MriPlanner TM platform. The generated sCT was automatically returned to the treatment planning system. A total of four different MR-scanners from two vendors and two magnetic field strengths were included in the study. For each patient, a CT-treatment plan was created and approved according to clinical practice. The generated sCT was rigidly registered to the CT, the structures transferred, and the clinical treatment plan was recalculated on the sCT. Separate external contours were generated based on the sCT and CT images respectively. The dose distributions from the CT-plan and the sCT-plan were compared based on a set of DVH-parameters and with gamma evaluation. Treatment techniques included VMAT, IMRT and conventional treatment using two commercially available treatment planning systems. Results The overall (multi-center/multi-vendor) mean difference between sCT and CT dose distribution were 0.23%±0.42% for PTV mean, 0.04%±0.27% for bladder mean and 0.16%±0.42% for rectum mean (1 s.d). Gamma evaluation showed a mean pass rate of 99.12%±0.63% in the complete body volume and 99.97%±0.13% in the PTV volume using a 2%/2mm global gamma criteria (1 s.d). The four centers showed similar results. All evaluated DVH-criteria were shown to be equivalent at a 95% confidence interval using a two one-sided test of equivalence for paired samples. Conclusion The results of the MR-OPERA study showed that an MRI only workflow using the MriPlanner was dosimetrically accurate for a variety of vendors, field strengths and treatment techniques. Minimal differences were observed between sCT and CT dose distributions, and in comparison to other uncertainties in radiotherapy, they can be considered negligible. The proposed method will allow for a straightforward implementation of an MRI only workflow for external prostate radiotherapy at most clinics. PV-0132 Comparison of planned versus simulated delivered dose in IMRT for endometrial cancer I. White 1 , D. McQuaid 1 , A. Dunlop 1 , N. Hopkins 1 , M. Caputo 1 , S. Mason 1 , S. Lalondrelle 1 1 The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Radiotherapy, Sutton, United Kingdom Purpose or Objective To quantify the planned versus the delivered radiation dose using deformable image registration of cone beam CT (CBCT), in patients treated with IMRT for endometrial cancer. Material and Methods 1. Post-hysterectomy patients treated with adjuvant IMRT (4500cGy in 25 fractions) for endometrial cancer were retrospectively dose tracked using CBCT on a commercial treatment planning system (RayStation v5, Raysearch Laboratories). 2. CBCTs were acquired days 1-4 and then weekly except when error >5mm. 3. Rigid registration between the planning CT and each CBCT was performed based on treatment position. 4. CBCT electron density values were established.