ESTRO 36 Abstract Book

S141 ESTRO 36 2017 _______________________________________________________________________________________________

HDR brachytherapy, using a phase-only cross correlation localization method. [1] Beld E. et al. 2015 Proc. Intl. Mag. Reson. Med. 24, #4151. [2] De Oliveira A. et al. 2008 MRM 59 1043-1050.

needle insertion errors caused by e.g. needle bending, (2) unpredictable anatomy movements such as prostate rotations (induced by the insertion or retraction of the needle), prostate swelling or intra-procedural rectum or bladder filling. In this study, a new adaptive dose planning strategy is proposed to assess the second challenge. The performance of this approach is evaluated by simulating brachytherapy procedures using data of 10 patients diagnosed with prostate cancer. Material and Methods Throughout HDR prostate brachytherapy, unpredictable anatomy movements may cause errors in dose delivery and potentially, this may result in failure to reach clinical constraints (e.g. for single fraction monotherapy: D95% PTV>19 Gy, D10% urethra<21 Gy, D1cc bladder<12 Gy and D1cc rectum<12 Gy). In this study, a novel adaptive dose planning pipeline for MR-guided HDR prostate brachytherapy using a single needle robotic implant device is proposed to address this issue (Figure 1a). The dose plan (needle track positions, source positions and dwell times) and needle insertion sequence are updated after each needle insertion and retraction with MR–based feedback on anatomy movements (cf. Figure 1b). The pipeline was assessed on moving anatomy by simulating MR-guided HDR prostate brachytherapy with varying number of needle insertions (from 2 to 14) for 10 patients. The initial anatomy of the patients was obtained using the delineations of the prostate tumor and the OAR considered (urethra, bladder and rectum) on MR images. Each needle insertion and retraction induced anatomy movements which were simulated in 2 steps: (1) a typical 3D rotation of the prostate was imposed (2) a regularization of the movement in space was then applied. The initial and final dose parameters were compared in the situations with and without update of dose plan and needle insertion sequence. Results The computation time for re-planning was less than 90 seconds with a desktop PC. The actual delivered dose improved with vs. without update of dose plan and needle insertion sequence: On average, the dose coverage of the PTV was higher in the situation with vs. without update (Figure 1c). Moreover, the difference increased with the number of needle insertions. The dose received by the PTV in the situation with re-planning was not significantly different compared to the initial dose plan. Finally, the dose to the OAR’s was not significantly different between the initial dose plan and the dose delivered in the situation with and without update. Conclusion This study proposes a new adaptive workflow with feedback on the anatomy movements for MR-guided HDR prostate brachytherapy with a single needle robotic implant device. The assessment of the pipeline showed that the errors in the dose delivered due to movement of anatomy can be compensated by updating the dose plan and the needle insertion sequence based on MRI.

OC-0276 Toward adaptive MR-guided HDR prostate brachytherapy – Simulation study based on anatomy movements M. Borot de Battisti 1 , B. Denis de Senneville 2 , G. Hautvast 3 , D. Binnekamp 3 , M. Peters 1 , J. Van der Voort van Zyp 1 , J.J.W. Lagendijk 1 , M. Maenhout 1 , M.A. Moerland 1 1 University Medical Center Utrecht, Departement of Radiotherapy, Utrecht, The Netherlands 2 UMR 5251 CNRS/University of Bordeaux, Mathematics, Talence, France 3 Philips Group Innovation, Biomedical Systems, Eindhoven, The Netherlands Purpose or Objective Dose delivery during a single needle, robotic MR-guided HDR prostate brachytherapy may be impaired by: (1)