ESTRO 36 Abstract Book

S88 ESTRO 36 _______________________________________________________________________________________________

S. Ken 1 , F. Arnaud 1 , R. Aziza 2 , D. Portalez 2 , B. Malavaud 3 , J. Bachaud 4 , P. Graff-Cailleaud 4 , S. Arnault 5 , A. Lusque 5 , T. Brun 1 1 Institut Universitaire du Cancer - Oncopole - Institut Claudius Regaud, Medical Physics and Engineering, Toulouse, France 2 Institut Universitaire du Cancer - Oncopole - Institut Claudius Regaud, Radiology, Toulouse, France 3 Institut Universitaire du Cancer - Oncopole - CHU de Toulouse, Urology, Toulouse, France 4 Institut Universitaire du Cancer - Oncopole - Institut Claudius Regaud, Radiotherapy, Toulouse, France 5 Institut Universitaire du Cancer - Oncopole - Institut Claudius Regaud, Bureau des Essais Cliniques, Toulouse, France Purpose or Objective Focal brachytherapy is proposed in our institute as an alternative treatment to active surveillance for low-grade prostate cancer (PCa). This study aims at characterizing the tumor focus and its margin with multiparametric Magnetic Resonance Imaging (mpMRI) in order to prepare the clinical protocol of focal brachytherapy. Material and Methods Patients pre-qualified for this study were positive for PCa (Gleason 3+3) on a previous standard biopsy series. New series of mp-MRI-guided and ultrasound-targeted biopsies were performed and in total, 17 patients with confirmed tumor and diameter<20mm were included in this phase II clinical trial (NCT01902680). mpMRI were acquired on a 1.5T Magnetom Aera Siemens scanner with 18-channel surface body coil. Anatomic imaging consists in Fast Spin Echo T2-weighted MRI (T2-MRI). In addition, same in- plane acquisition of functional Diffusion Weighted MRI (DWI-MRI) and Dynamic Contrast Enhanced MRI (DCE-MRI) were performed. After mpMRI registration, tumor volumes of interest (VOI) were drawn on anatomic T2-MRI. VOI and VOI+2mm were reported on functional DWI-MRI and DCE-MRI (Figure 1). Extracted parameters were Apparent Diffusion Coefficient (ADC) and KTrans. All parameters distributions were analyzed with Olea Sphere v3.0 and compared to contralateral normal appearing tissue. Focal brachytherapy was then delivered to all patients with linked 125 I seeds with a dose prescription of 152 Gy on the Planning Target Volume (PTV=VOI+2mm).

Conclusion This study confirms that mpMRI is a non-invasive technique able to characterize tumor margin in low-grade PCa. Tumor characterization and delineation is a crucial step in focal brachytherapy as only sub-volume of the prostate is treated with high gradient dose levels. Target volume margin definition is a hot topic when focal treatments (e.g. cryotherapy or HIFU) are considered and mpMRI can bring quantitative answers. OC-0172 interstitial salvage HDR-brachytherapy for recurrent prostate cancer after radiation therapy P. Jiang 1 , C. Van der Horst 2 , B. Kimmig 1 , F. Zinsser 1 , B. Poppe 3 , U. Luetzen 4 , K.P. Juenemann 5 , F.A. Siebert 1 , J. Dunst 1 1 UKSH- Campus Kiel, Department of Radiation Oncology, Kiel, Germany 2 Community Clinic Kiel, Department of Urology-, kiel, Germany 3 Medical Campus Pius-Hospital- Carl von Ossietzky University, University Clinic for Medical Radiation Physics-, Oldenburg, Germany 4 UKSH- Campus Kiel, Department of Nuclear Medicine, Kiel, Germany 5 UKSH- Campus Kiel, Department of Urology, Kiel, Germany Purpose or Objective There is growing literature on local salvage treatments following definitive radiation. However, data employing interstitial high dose rate brachytherapy (HDR-BT) for salvage treatment are rare, especially those with long- term outcomes. This is a report of our results as a unique published cohort with salvage HDR-BT after previous HDR- BT treatment (Jiang et. al. 2016, brachytherapy, paper in pressed). Emphasis was put on 5-year outcome and toxicity. Material and Methods From 2009 to 2014, 29 patients with local failure after previous radiotherapy for prostate cancer were treated with salvage interstitial HDR-BT. Primary treatment was combined external beam irradiation (EBRT) with 50Gy plus HDR-BT-boost with 30 Gy in 27 patients. The primary treatment carried the total dose to a combined biologic equivalent dose in 2 Gy per fraction of about 178 Gy, by assuming an α/β ratio of 1.5 for the tumor and about 146 Gy by an α/β ration of 3. 2 patients had undergone EBRT with 66.6 Gy of the prostate bed as salvage treatment after prostatectomy. The interval between primary treatment and salvage treatment was 5.5 years (mean ± SD: 5.5 ± 2.8 years). All 29 patients had biochemical failure according to the Phoenix definition. The diagnosis of local recurrence was made on the basis of F-18 labeled cholin-PET. The presence or co-existence of regional lymph node and/or distant metastases was excluded by imaging methods.

Results ADC parameters (mean, median, 25th and 75th percentiles) are found to be significantly lower in tumor volume (VOI) compared to contralateral normal tissue (p<0.012 for all ADC parameters), confirming diffusion tumor mass restriction. Different distributions of ADC and Ktrans were observed among patients (Figure 2). Majority (66.66%) of low ADC and abnormal Ktrans values were included in the VOI. Interestingly, the 2mm margin allows us to treat additional abnormal ADC and KTrans volumes on 1/3 of the patients.