Abstract Book

S861

ESTRO 37

Results 185 pts (88 ADV/87 SALV) with complete data at baseline and at 1 year were analysed. For 104 of these, data at 2 years were also available. Median baseline, 1- and 2 year ANX were 3 vs 4, 2 vs 2.5 and 2 vs 2 in ADV and SALV cohorts, respectively, The corresponding values for DEP were 2.5 vs 3, 2 vs 2 and 1 vs 2. At MVA, 1-year urinary intermittency and UI were the only 2 variables independently predictive of both ANX and DEP (Tab. 1). Two-year UI and nocturia independently predicted the risk of 2-year ANX, while 2-year UI was the only covariate independently predictive of 2-year DEP (Tab. 1).

PTV. To study the potential association to the bladder trigone on long-term urinary function, the bladder trigone was MR-based contoured too. An indwelling catheter was inserted to aid in the delineation of the urethra. The request for dose prescription is that V100%>95% of the PTV. The rectal dose-volume goals were V50% <50%, V80% <20%, V90<10%, V100%<5%. The bladder dose-volume goals were V50% <40%, V92.4% < 12.7%, V100% <10%. Concerning the urethra and the trigone, the constraints for the maximum dose (Dmax) were Dmax<39.9 Gy and Dmax<38.9 Gy, respectively. The IGRT protocol is based on 3 intraprostatic fiducial markers, with daily online checks by CBCT. The acute toxicity gastrointestinal (GI) and genitourinary (GU) were recorded using the RTOG/EORTC scale. Additional data are collected by means of I-PSS (International Prostate Symptom Score) e IIEF-5 (International Index of Erectile Function) questionnaires. Results Between November 2015 and July 2017, 30 patients were enrolled in this prospective study, the median follow-up duration was 6 months (range, 3-18 months). The median age was 74 years (range, 60–81 years). The mean target registration error was 0.3±0.2 mm (1SD). The CT- contoured prostate resulted on average 35% larger that the true gland (MR-based volume) with a mean DICE coefficient of 0.79 (range: 0.61–0.90), such that posterior portions were always missed and anterior normal tissue always included. For the dose distributions of the organs at risk, all the dose constraints were largely satisfied. Acute GU and GE toxicity of grade 2 were observed in 26% and 10% patients respectively. The quality of life assessment showed a complete recovery of obstructive symptoms 3 months from the end of the radiotherapy. Conclusion Our study showed an important reduction in volume of MR-guided prostate, in agreement with literature data. This allows safe high dose per fraction prostate with limited acute toxicities. EP-1600 Comparison of patterns of implantation for the 3 spacers for radiation therapy for prostate cancer. I. Latorzeff 1 , D. Marre 2 , G. Jimenez 1 , J. Mazurier 2 , P. Dudouet 1 , F. Jonca 3 , P. Seguin 4 , P. Labarthe 5 , J. Guillotreau 6 , G. Ploussard 7 , E. Bruguiere 8 1 Oncorad Garonne- Clinique Pasteur, Radiotherapy- Oncology, Toulouse, France 2 Oncorad Garonne- Clinique Pasteur, Physics, Toulouse, France 3 Clinique Ambroise Paré, Urology, Toulouse, France 4 Clinique Occitanie, Urology, Muret, France 5 Clinique des Cèdres, Urology, Cornebarrieu, France 6 Clinique Pasteur, Urology, toulouse, France 7 Clinique Saint Jean Languedoc, Urology, Toulouse, France 8 Clinique Pasteur, Radiology, Toulouse, France Purpose or Objective To study, after implant of a spacer, the anatomical and radiological parameters with MRI of installation between the 3 spacers Material and Methods Since September 2013, 46 patients, mean age 75 years, were implanted with a spacer by a single radiologist, in a space created between the prostate and the rectum (biodegradable balloon (BB), acid hyaluronique gel (AH) and polyethylene glycol gel(PEG)), before starting

Conclusion No significant differences in terms of risk of both baseline and long-term ANX and DEP were observed between pts treated with ADV or SALV RT. One- and two-year urinary incontinence was a strong predictor of long-term ANX and DEP. An independent role of urinary intermittency in impairing both psychological disturbances at 1 year, as well as of nocturia in increasing the risk of 2-year ANX, also emerged. EP-1599 MRI-guided contouring in SBRT of the prostate for localized disease A. Magli 1 , E. Moretti 2 , M. Guernieri 2 , M. Urpis 1 , A. Prisco 1 , M. Crespi 2 , C. Foti 2 , P. Scalchi 2 , M. Trovo' 1 1 ASUIUD, Department of Radiation Oncology, Udine, Italy 2 ASUIUD, Medical Physics / Fisica Sanitaria, Udine, Italy Purpose or Objective Magnetic resonance imaging (MRI)-guided stereotactic body radiation therapy (SBRT) has been established as a safe and effective treatment for prostate cancer. To evaluate the acute toxicity of a phase II study concerning SBRT with a dose scheme of 36.25 Gy in 5 fractions, in patients with localized prostate cancer at low/intermediate risk (according to NCCN score) and risk of lymph node involvement <17% ( Roach Index). Material and Methods This study dealt with a prospective analysis of the 30 patients treated with SBRT using VMAT technique. The GTV (prostate with the 1/3 proximal seminal vesicles) was delineated using the MR T2-weighted (T2w) and FLAIR images, co-registered with planning-CT images. Our local rigid registration method employed the 3 intraprostatic gold fiducial markers (GFM) as landmarks. The GTV was delineated also on CT-images and compared to MR-based GTV, by using the DICE metric. All patients were contoured under the supervision of the same physician (AM). For the planning, an isotropic margin of 6 mm around the MR-based GTV is added to obtain the