ESTRO 2022 - Abstract Book

S500

Abstract book

ESTRO 2022

Materials and Methods The instrument utilizes the commercial HDR BT outer catheter and an inner needle with internal compliant mechanism. This mechanism enables distal tip steering through proximal instrument bending while preserving high axial and flexural rigidity. Active steering of the instrument allows for adjustments of the catheter pathway and withdrawal of the inner needle creates a work channel for remote afterloading. Finite element analysis evaluates the design and the prototype is validated in experiments involving tissue simulants and ex-vivo bovine tissue. US images are used to provide visualization and shape-reconstruction of the instrument during the insertions. Results Manually controlled active needle tip steering in inhomogeneous tissue simulants and ex-vivo tissue resulted in mean targeting errors of 1.4 mm and 2 mm in 3D position, respectively. We found lateral tip steering up to 20 mm. The experiments showed that the steering response of the instrument is history-independent. Conclusion The results indicate that the endpoint variability of the steerable needle is similar to that of a conventional rigid HDR BT implant needle while adding the ability to steer along curved paths. High axial and flexural rigidity enable puncturing and path control within various heterogeneous tissues. The developed steerable instrument has the potential to overcome problems currently unavoidable with rigid HDR BT implant needles, such as PAI, without major changes to the clinical workflow. K. Sritharan 1,2 , H. Akhiat 3 , D. Cahill 4 , S.L. Choi 5 , A. Choudhury 6 , P. Chung 7 , J. Diaz 3 , L. Dysager 8 , W. Hall 9 , L. Kerkmeijer 10 , C.A. Lawton 9 , J. Murray 1,2 , C.J. Nyborg 11 , F.J. Pos 12 , M. Rigo 13 , T. Schytte 11,14 , M. Sidhom 15 , A. Sohaib 16 , A. Tan 17,18 , J. van der Voort van Zyp 19 , D. Vesprini 20 , M.J. Zelefsky 21 , A. Tree 1,2 1 Royal Marsden Hospital NHS Foundation Trust, Radiotherapy, Sutton, United Kingdom; 2 Institute of Cancer Research, Radiotherapy and Imaging, London, United Kingdom; 3 Elekta AB, Elekta, Stockholm, Sweden; 4 Royal Marsden Hospital NHS Foundation Trust, Urology, London, United Kingdom; 5 MD Anderson Cancer Centre, Radiation Oncology, Houston, USA; 6 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom; 7 Princess Margaret Cancer Centre, Radiation Oncology & Radiation Medicine Program, Toronto, Ontario, Canada; 8 Odense University Hospital, Oncology, Odense , Denmark; 9 Medical College of Wisconsin, Radiation Oncology, Milwaukee, Wisconsin, USA; 10 Radboud University Medical Centre, Radiation Oncology, Nijmegen, The Netherlands; 11 Odense University Hospital, Oncology, Odense, Denmark; 12 The Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands; 13 IRCCS Sacro Cuore Don Calabria Hospital, Advanced Radiation Oncology, Negrar Di Valpolicella, Verona, Italy; 14 University of Southern Denmark, Clinical Research, Odense, Denmark; 15 Liverpool Hospital, Cancer Therapy Centre, Liverpool, New South Wales, Australia; 16 Royal Marsden Hospital NHS Foundation Trust, Radiology, Sutton, United Kingdom; 17 Townsville Cancer Centre, The Townsville Hospital, Radiation Oncology, Townsville, Queensland, Australia; 18 James Cook University, Oncology, Townsville, Queensland, Australia; 19 University Medical Centre Utrecht, Radiation Oncology, Utrecht, The Netherlands; 20 Sunnybrook Health Sciences Centre, University of Toronto, Radiation Oncology, Toronto, Ontario, Canada; 21 Memorial Sloan Kettering Cancer Centre, Radiation Oncology, New York, USA Purpose or Objective Up to a third of patients who have a radical prostatectomy for localised prostate cancer will have a rising PSA post- operatively and salvage radiotherapy is a curative treatment option in this setting. Accurate delineation of the target remains the ‘weakest link’ in the radiotherapy planning process. Pelvic anatomy is better visualised on MR compared to CT due to a higher soft tissue resolution and may facilitate CTV delineation, yet it’s use in prostate bed radiotherapy planning is limited. Current guidelines for prostate bed CTV delineation are primarily based on CT and can differ considerably. This is a multicentre international contouring study which aims to assess the degree of interobserver variability for prostate bed CTV delineation on MRI amongst experienced clinical and radiation oncologists. Materials and Methods In total, 22 observers, predominantly experienced radiation/clinical oncologists, were invited to take part in the study. Each participant was provided with T2W Elekta Unity MR-linac scans for three patients post prostatectomy. A clinical vignette containing the patient’s history, diagnostic MRI report, histopathology report and the baseline prostate mpMRI scan were provided. Observers were asked to outline the prostate bed CTV using the information provided as per their current clinical practice, on ProKnow, a cloud-based contouring software. On completion, the contours were imported into the ADMIRE research version 2.0 (Elekta AB, Stockholm, Sweden) program. A Simultaneous Truth and Performance Estimate (STAPLE) was created for each case and interobserver comparisons were then carried out by comparing each observer’s individual contour to the STAPLE structure. Results A total of 19 observers partook in this study; 17 radiation/clinical oncologists, 1 urological surgeon and 1 radiologist, from a total of 11 institutions in 7 countries. Only the contours drawn by the oncologists were used to create the STAPLE. A totally of 51 contours were analysed, of which three were not included for technical reasons. Figure 1 demonstrates the median results for four comparison metrics. Figure 2 demonstrates visually the variability seen for one of the cases. On Poster Discussion: 14: Urology 2 PD-0571 Determining interobserver variability in prostate bed CTV target delineation using MRI