ESTRO 38 Abstract book

S34 ESTRO 38

minimum of 0.3 s. Due to limitations in the temporal resolution of the system, dwell times of less than 0.3 s could not be resolved for reconstruction, resulting in 175/200 dwell positions being reconstructed. Figure (b) shows the reconstructed prostate volume taken from the TRUS, co-registered with the reconstructed dwell positions from the BrachyView system and CT determined dwell locations. Figure (c), shows the configuration of the experiment.

ranging from 24-60 Gy in 3-8 fractions. Thirty-two percent of patients received concurrent immunotherapy or targeted therapies. Median follow-up was 11.6 months. In 48% of patients, acute grade 1-2 toxicities (CTCAE v4) were reported, mostly fatigue and nausea. Acute grade 3 nausea and weight loss were observed in one patient. Another developed a lumbar insufficiency fracture six months post-SMART, a possible late grade 3 adverse event. Only one in-field tumor recurrence was observed eight months post-SMART, resulting in a 1-year LC of 93%. The 1-year DFS and OS rates were 47% and 76%, respectively. Conclusion Delivery of SMART to adrenal oligo-metastasis is associated with limited acute toxicity, even in a cohort where 32% of patients received concurrent immune and targeted therapies. Local control rates are promising, but long-term follow-up is awaited. OC-0073 BrachyView: A Real-time In-body HDR Source Tracking System with Simultaneous TRUS Image Fusion S. Alnaghy 1 , D. Cutajar 1 , M. M. Safavi-Naeini 1 , G. Stuart 1 , H. Andrew 2 , A. Bece 2 , J. Jakubek 3 , S. Pospisil 3 , M. Lerch 1 , M. Petasecca 1 , A. Rosenfeld 1 1 University of Wollongong, Centre for Medical Radiation Physics, Wollongong, Australia; 2 St George Hospital, St George Cancer Care Centre, Kogarah, Australia; 3 Czech Technical University of Prague, Institute of Experimental and Applied Physics, Prague, Czech Republic Purpose or Objective HDR BrachyView is a real-time in-body gamma camera probe for 3D HDR prostate brachytherapy source tracking, providing real-time source position verification. This study constitutes the first experimental demonstration of the HDR BrachyView prototype, performed with a CIRS tissue- equivalent gel prostate phantom. The main objectives of this study are to evaluate the developed real-time acquisition software in terms of the accuracy of spatiotemporal source position estimation, and to evaluate the combination of BrachyView reconstructed positions and dwelling times and the 3D TRUS image data using a custom developed visualisation software. Material and Methods A prototype in-body gamma camera system with integrated TRUS and associated real-time image acquisition and analysis software was developed for intraoperative source tracking in HDR brachytherapy. The probe utilises a cylindrical 7-pinhole tungsten collimator and a 4×1 array of Timepix high-resolution pixelated silicon detectors. The developed real-time data acquisition and image fusion software is validated against CT measurements of source position during a full clinical treatment plan. The tracking accuracy and temporal resolution of the system was validated experimentally using a deformable tissue-equivalent prostate gel phantom and a full clinical HDR treatment plan. A global coordinate system was defined by CT scanning the phantom with the probe in situ. Fusion of the estimated source dwell positions and timing with the 3D prostate image was performed using an integrated 3D visualisation software. Results Figure 1 (a) shows the percentage of the reconstructed dwell positions distribution as a function of the discrepancy of the position in respect to the nominal location determined by the TPS and identified in the CT scan of the phantom using implanted CT markers in each catheter. The BrachyView system was able to measure 78% of the 200 source positions with an accuracy within 1 mm. A minimum acquisition time of 0.28 s/frame was required to achieve this accuracy, restricting dwell times to a Proffered Papers: BT 1: Treatment verification

Conclusion HDR BrachyView is demonstrated to be a valuable tool for intraoperative source tracking in HDR brachytherapy. It can resolve source dwell locations in real-time and potentially in-vivo, with the advantage to visualise the source positions within the prostate anatomy when combined with TRUS. However, a faster readout system combined with a more efficient source localisation algorithm is required to be able to maximise the number of reconstructed dwell positions with short dwell times. OC-0074 Accuracy of an integrated EMT/BT system for dwell-position detection in pelvic BT L. Van Heerden 1 , J. Schiphof-Godart 1 , M. Christianen 1 , J. Mens 1 , M. Franckena 1 , M. Maenhout 1 , R. Rijnsdorp 1 , L. Purpose or Objective Recently, a prototype High-Dose Rate Brachytherapy (HDR-BT) Flexitron afterloader with integrated Electromagnetic Tracking (EMT) has been developed by Elekta AB, enabling pre-treatment in-vivo verification of dwell positions. However, electromagnetic interference originating from surrounding equipment present during HDR-BT procedures could lead to dwell-position detection errors. As of yet, this has not been investigated for the integrated system in various clinical environments for pelvic brachytherapy. The goal of this study is to assess the impact of the interference on the accuracy of EMT- based dwell-position detection in prostate and cervix HDR- BT. Material and Methods Dedicated prostate and cervix phantoms were constructed holding an implant of 10 catheters and the Utrecht applicator with 6 needles, respectively. CT scans of the phantoms were acquired to reconstruct the implant geometry. Subsequently, BT plans were created with dwell positions at every 5mm. These BT plans were verified by EMT in an interference-free set-up and in Luthart 1 , M. Hoogeman 1 , I. Kolkman-Deurloo 1 1 Erasmus Medical Center, Radiation Oncology, Rotterdam, The Netherlands