ESTRO 38 Abstract book

S824 ESTRO 38

(N=12) and PT (N=7). All parameters values are given as median in the "Results" section.

dosimetric factors were smaller in PLPC receiving AT than in PLPC did not undergo AT. Dosimetric factors of the bladder and other coexistent statuses were not significant.

Results Figure 2 presents the violin plots relative to parameters derived from mpMRI. Distributions of ADC, D (10 -3 mm 2 /s), KTrans (min -1 ) and computed b2000 (s/mm 2 ) are shown according to the regions of interest (VOI or CONTRO) and the groups (PCa or PT). For PCa group, ADC and D parameters inside the VOIs were significantly lower than in the CONTRO: 1.23 [0.66-1.62] vs. 1.48 [1.13-1.67] (p=0.0022) and 0.93 [0.59-1.49] vs. 1.33 [0.94-1.57] (p=0.0022), respectively. Voxels intensity of computed b2000 was significantly higher: 37.87 [28.29- 87.11] vs. 27.63 [23.04-77.81] (p=0.0037). KTrans values were also significantly higher in the VOIs compared to CONTRO: 0.54 [0.05-1.10] vs. 0.36 [0.06-0.91] (p=0.0414). For PT group, ADC values were significantly lower inside the VOIs compare to CONTRO: 1.30 [0.98-1.43] vs. 1.43 [1.06-1.62] (p=0.0280). Computed b2000 values were significantly higher inside the VOIs: 46.45 [27.32-80.18] vs. 38.75 [25.66-70.20] (p=0.0180). D and KTrans were not significantly different between the VOIs and CONTRO: p=0.0630 and p=0.1282, respectively. Volume of normal ADC (1 st and 3 rd quartile range) inside the VOIs were significantly smaller in the PCa group compared to the PT group: 12.2% [4.3-43.8] vs. 36.7% [8.7- 50.9] (p=0.0346). Volume of low ADC (<1 st quartile) was more important in the PCa group compared to the PT group: 72.7% [52.6-95.4] vs. 51.1% [16.7-84.4] but at the limit of significance (p=0.0519).

Conclusion PLPC with AT appeared to be more critical than doses in PU on severe late urinary toxicity. EP-1524 Differentiation between adenocarcinoma and prostatitis with multi-parametric MRI S. Ken 1 , R. Aziza 2 , D. Portalez 2 , L. Chaltiel 3 , J. Gilhodes 3 , T. Brun 4 1 Institut Universitaire du Cancer - Oncopôle- Institut Claudius Regaud, Department of Engineering and Medical Physics, Toulouse, France ; 2 Institut Universitaire du Cancer - Oncopôle - Institut Claudius Regaud, Department of Medical Imaging, Toulouse, France ; 3 Institut Universitaire du Cancer - Oncopôle - Institut Claudius Regaud, Department of Clinical trial, Toulouse, France ; 4 Institut Universitaire du Cancer - Oncopôle - Institut Claudius Regaud, Department of Engineering and Medical Physics, Toulouse, France Purpose or Objective In our institute, patients with low-to-moderate risk of prostate cancer could benefit from ultra-focal brachytherapy [1] as an alternative treatment to active surveillance. However, radiological diagnosis, which will guide the treatment strategy, remains challenging and still needs confirmed biopsies to distinguish between prostatic adenocarcinoma (PCa) and prostatitis (PT). This study aims at identifying imaging biomarkers derived from multi-parametric MRI (mpMRI) to help for the differentiation between PCa and PT. Material and Methods Nineteen patients with low-to-moderate risk of prostate cancer underwent mpMRI on a 1.5T system (Magnetom Aera, Siemens Healthcare). Anatomical T2-weighted, IVIM diffusion (11b-values 0-800 s/mm 2 ) and T1-weighted perfusion series were acquired. Volumes of interest (VOIs, in blue on Figure 1) were contoured on T2 images and reported on KTrans, ADC, D and computed b2000 maps. Distributions of voxel values inside the VOIs were compared to contralateral normal appearing tissue (CONTRO, in green on Figure 1) delineated with careful attention to get equivalent volume size for comparison. Volumes repartitions according to quartiles were compared between the biopsy confirmed groups of PCa

Conclusion Abnormally low D parameters derived from IVIM and high KTrans parameters derived from perfusion MRI were found in the adenocarcinoma group but not in the prostatitis one. Percentage volumes distribution of ADC was also able to distinguish between the two groups. [1] Brun et al. Brachytherapy 2018 https://doi.org/10.1016/j.brachy.2018.01.011 EP-1525 Postoperative radiation therapy following radical prostatectomy in Stockholm County in 2008- 2016 J. Falk 1 , M. Aly 2 , T. Nordström 3 , A. Valdman 4 1 Karolinska University Hospital, Deptartment of radiation therapy, Stockholm, Sweden ; 2 Karolinska University Hospital, Department of Urology, Stockholm, Sweden ; 3 Danderyd Hospital, Department of Urology, Stockholm, Sweden ; 4 Karolinska University Hospital, Department of Radiation Therapy, Stockholm, Sweden