ESTRO 2020 Abstract Book

S265 ESTRO 2020

OC-0472 A potential multi-model AI framework for MRI motion correction and fast image acquisition in RT

Abstract withdrawn from presentation

OC-0473 Evaluation of first 20 patients treated with MR-Only prostate radiotherapy with MR-CBCT matching J. Wyatt 1,2 , R.A. Pearson 1,2 , J. Frew 1 , C. Walker 1 , N. Richmond 1 , M. Wilkinson 1 , K. Wilkes 1 , S. Driver 1 , S. West 1 , K. Pilling 1 , R.L. Brooks 1 , D. Ainslie 1 , E. Wilkins 1 , H.M. McCallum 1,2 1 Newcastle upon Tyne Hospitals, Northern Centre for Cancer Care, Newcastle upon Tyne, United Kingdom ; 2 Newcastle University, Northern Institute for Cancer Research, Newcastle upon Tyne, United Kingdom Purpose or Objective MR-only radiotherapy removes the need for a planning CT, enabling the superior MR soft-tissue to be used for delineation without the MR-CT registration uncertainty. MR-CBCT soft-tissue matching removes the need for implanted fiducial markers, which is essential for extending MR-only treatments to other clinical sites but has not been previously reported. This paper presents an evaluation of the first clinical implementation of MR-only radiotherapy using MR-CBCT soft-tissue matching. Material and Methods 20 patients received planning MR and CT scans on a radiotherapy couch top. All patients were delineated, planned and treated using the MR alone, with the CT scan used for QA purposes only. Two MR sequences were acquired: a small Field Of View (FOV) MR image for target delineation and a large FOV MR image for Organs At Risk (OAR) delineation, synthetic CT (sCT) generation and on-treatment verification. The sCT was produced using MriPlanner (Spectronic Medical, Sweden) and the VMAT plan created using RayStation (RaySearch Laboratories, Sweden). For on-treatment verification the CBCT was matched to the large FOV MR, which was relabelled as a “CT” in the DICOM header so it could be used on the TrueBeam linear accelerator (Varian, Palo Alto, USA). The prostate and seminal vesicles were independently delineated using the back-up CT fused with the small FOV MR. The volume ratio between MR-only prostate and seminal vesicles volume and the MR-CT volume was calculated. The sCT dose calculation accuracy was evaluated by registered the CT to the sCT and recalculating the MR-only plan on the CT. The dose difference to the PTV D50 was calculated and the doses compared using a gamma analysis. The CBCT matching accuracy was assessed by two radiographers independently matching the first fraction CBCT to the backup CT and comparing to the clinical MR-CBCT match. Results The prostate and seminal vesicle volumes were smaller for the MR-only pathway than using the MR-CT fusion, with the volume ratio being V = 86 ± 2 % (mean ± sem). The sCT dose calculation was accurate, with a mean dose difference in the PTV D50 of ∆D=0.2±0.1% (range - 0.5%,1.0%) . The mean gamma pass rate within the body contour with gamma criteria 1%/1mm was (range 95.6%, 99.4%). See fig 1 for example sCT dose distribution and MR- CBCT match.

Fig 1 The differences between the clinical MR-CBCT match and the mean of the backup CT-CBCT matches were small (fig 2), with mean differences 0.1 ± 0.4 mm, 0.1 ± 0.4 mm, - 0.2 ± 0.2 mm for the vertical, longitudinal and lateral axes respectively.

Fig 2

Conclusion MR-only radiotherapy with soft-tissue matching has been successfully clinically implemented to our knowledge for the first time. The MR-only pathway produced smaller target volumes with high dosimetric and on-treatment matching accuracy. This implies that MR-only prostate radiotherapy can be safely delivered using MR-CBCT soft- tissue matching without fiducial markers, enabling MR- only radiotherapy to be extended to other pelvic cancers. OC-0474 Feasibility of prostate SBRT with DIL boost in various platforms: A Crowd Knowledge based study A. Savini 1 , E. Villaggi 2 , O. Blanck 3,4 , C. Moustakis 5 , V. Hernandez 6 , S. Russo 7 , M. Esposito 7 , R. De Blas Piñol 8 , N. Hardcastle 9 , J. Saez 10 , R. Doro 11 , M.D. Falco 12 , V. Silvestri 13 , B. Nardiello 14 , S. Broggi 15 , L. Strigari 16 , S. Cilla 17 , S. Strolin 18 , M. Stasi 19 , P. Mancosu 20 1 Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori IRST IRCCS, Medical Physics, Meldola, Italy ; 2 AUSL Piacenza, Medical Physics, Piacenza, Italy ; 3 University Medical Center Schleswig-Holstein, Radiation Oncology, Kiel, Germany ; 4 Saphir Radiosurgery Center- Frankfurt and Northern Germany, Radiation Oncology, Güstrow, Germany ; 5 University Hospital Münster, Medical Physics, Münster, Germany ; 6 Hospital Universitari Sant Joan de Reus, Medical Physics, Tarragona, Spain ; 7 Azienda USL Centro Toscana, Medical Physics, Florence, Italy ; 8 Institut Catala d'Oncologia- Hospitalet, Medical Physics, Barcelona, Spain ; 9 Peter MacCallum Cancer Centre, Medical Physics, Melbourne, Australia ; 10 Hospital Clinic de Barcelona, Medical Physics, Barcelona, Spain ; 11 University of Florence- Istituto Fiorentino di Cura ed Assistenza IFCA, Medical