Abstract Book

S831

ESTRO 37

Purpose or Objective The change in prostate size for intensity-modulated radiotherapy (IMRT) planning in patients with small prostate glands has not yet been elucidated. If the size of prostate was changed, the cover of radiation dose is influenced. Therefore, we evaluated the relatively small changes in prostate size during IMRT using MRI and CT. Material and Methods A total of 24 consecutive patients with prostate cancer were enrolled in the study. Two gold fiducial markers were placed on the prostate 3 weeks before planning CT/MRI examination. MR imaging was performed at three time points. The initial MRI was performed prior to the start of radiotherapy. Second MRI was performed at 38 Gy (range: 36–40 Gy), which represented the halfway point of the radiotherapy course. The last MRI was performed on the day of completion of the radiotherapy course (76 Gy range: 74–78 Gy). We made a replan (adaptive plan) for all cases. We evaluate whether the outcome of DVH were same in initial plan and replan or not using size change of prostate and organ at risk. Results There was no significant difference between the estimated sizes of prostate during RT in all three phases (Figure 1). Volume of bladder wall was changed but which did not influence DVH. Volume of rectal wall was not changed in all phases. Replan at a point of second MRI was well implemented in all patients in the regulation of first dosimetric parameters.

Electronic Poster: Clinical track: Prostate

EP-1538 Combining EBRT and HDR-BT in high-risk prostate cancer: an effective and safe experience D. Candini 1 , F. Lopez-Campos 1 , T. Muñoz 1 , M. Martín 1 , C. Vallejo 1 , A. Hervás 1 1 Hospital Ramon y Cajal, Radiation Oncology, Madrid, Spain Purpose or Objective To evaluate acute and sub-acute genitourinary (GU) and gastrointestinal (GI) toxicity after external beam radiotherapy (EBRT) and a boost of High-Dose-Rate Brachytherapy (HDR-BT) in high-risk prostate cancer patients. Material and Methods Patients with prostate cancer, histologically confirmed, were enrolled. Selection criteria included: M0; high-risk features, according to NCCN and EAU guidelines; no trans-urethral resection of the prostate in the previous twelve months; no anesthesiological contraindications. All patients received hypofractionated and image-guided EBRT by volumetric IMRT technique to a dose of 37.5 Gy in 15 fractions combined with a single 15 Gy HDR-BT ( 60 Co multi-source) dose, two weeks later EBRT. All patients assumed androgen deprivation therapy for two years. Dosimetrical parameters and acute/sub-acute toxicity (according to the CTCAE Version 4.03) were collected. Results Between May 2015 and March 2017, 58 patients were treated by the reported schedule. No post-HDR procedure complications were detected in all patients and the procedure resulted feasible in terms of workload organization. Median follow-up was 20 months. The dosimetrical constraints evaluated were D2 cc < 9.75 Gy for rectal volume, and D10 cc < 17.25 Gy for urethra. They were respected in 100% of cases. The schedule was well tolerated. No patient developed GI and GU acute or sub-acute toxicity ≥ G3. All patient presents biochemical control. Conclusion This schedule is feasible and well tolerated with low morbidity and associated with excellent short and medium-term disease control rates. Ongoing and planned accrual of more patients and a longer follow-up will allow confirming these results EP-1539 No change in prostate size during radiotherapy with 2 Gy fractions for small size prostates O. Tanaka 1 , H. Komeda 2 , S. Hiose 3 , E. Yama 4 , T. Taniguchi 5 , M. Matsuo 6 1 Murakami Memorial Hospital- Asahi University, Department of Radiation Oncology, Gifu, Japan 2 Gifu Municipal Hospital, Department of Urology, Gifu, Japan 3 Gifu Municipal Hospital, Division of Radiation Service, Gifu, Japan 4 Gifu Municipal Hospital, Department of Radiation Oncology, Gifu, Japan 5 Murakami Memorial Hospital, Department of Radiation Oncology, Gifu, Japan 6 Gifu University School of Medicine, Department of Radiology, Gifu, Japan

Conclusion In this study, no significant change in prostate size was observed during the course of IMRT. The outcome of DVH from same regulation (initial and second) is mostly same. It is not necessary to reevaluate the size of the prostate during a radiotherapy period. EP-1540 Radiation therapy for patients with paraaortic lymph nodes metastases of prostate cancer P. Bulychkin 1 , S. Tkachev 1 , A. Nazarenko 1 1 N. N. Blokhin Cancer Research Center- Russian Academy of Medical Sciences, radiation oncology, Moscow, Russian Federation Purpose or Objective The purposes of our study were to create and integrate a new scheme of radiation therapy for patients with paraaortic lymph nodes metastases of prostate cancer. Material and Methods Patients with paraaortic lymph nodes metastases of prostate cancer after definitive and salvage radiation therapy were treated by radiation therapy alone or with concurrent hormone therapy. Radiotherapy have been prescribed to the all paraaortic lymphatic nodes to 40-44 Gy of 2-2.5 Gy in the first stage. Then the PET-