ESTRO 2023 - Abstract Book

S1595

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ESTRO 2023

dosimetric parameters, urethra doses, and femur doses, however, did not differ significantly. The dose homogeneity was worse in SIB 40 Gy plan compared to SIB 37.75 Gy plan. Likewise, the number of segment and monitor units did not significantly differ between plans. Conclusion This is the first dosimetric study to evaluate the dose escalation using the simultaneous integrated boost technique in prostate cancer patients treated with high field1.5-Tesla MR-LINAC. Our study demonstrated that increasing the dose of IPL up to 40 Gy in 5 fractions is dosimetrically feasible, with the exception of an increase in bladder maximum doses and dose homogeneity. As a result, this study paves the way for future clinical trials of the dose escalation SBRT regimen in prostate cancer patients. M. Schrader 1 , H. Garcia Schüler 1 , A. Kishan 2 , B. Atalar 3 , L. Boldrini 4 , S. Ehrbar 1 , H. Igaki 5 , J. Leeman 6 , R. Mak 7 , E. Mellon 8 , I. Nilo 1 , H. Nagar 9 , A. Pedersen 10 , E. Ozyar 11 , P. Parikh 12 , J. Dolan 12 , S. Perryck 1 , L. Placidi 4 , M. Steinberg 2 , M. Marchesano 13 , P. Maingon 14 , S. Tanadini-Lang 1 , L. Wilke 1 , N. Andratschke 1 1 Unispital Zürich, Radio-Onkologie, Zürich, Switzerland; 2 University of California, Radiooncology, Los Angeles, USA; 3 Maslak Acibadem Maslak Hospital Istanbul, Radiation Oncology, Istanbul, Turkey; 4 Fondazione Policlinico Universitario Agostino Gemelli, IRCCS, Rome, Italy; 5 National Cancer Center, Radiooncology, Tokyo, Japan; 6 Dana-Farber Cancer Institute, Harvard Medical School, Boston, USA; 7 Mass General Brigham, Radiooncology, Brigham, USA; 8 University of Miami, Sylvester Comprehensive Cancer Center, Miller School of Medicine, Miami, USA; 9 NewYork-Presbyterian, Weill Cornell Medicine , Ithaca, USA; 10 Rigshospitalet, Oncology, Copenhagen, Capital Region, Denmark; 11 Maslak Acibadem Maslak Hospital, Department of Radiation Oncology,, Istanbul, Turkey; 12 Henry Ford Health - Cancer, Radiation Oncology, Detroit, USA; 13 Ospedale FBF San Pietro, Radiooncology, Rome, Italy; 14 Hôpital de la Salpêtrière, Radiooncology, Paris, France Purpose or Objective Patients with cardiac implantable electronic devices (CIEDs) represent a critical cohort concerning radiotherapy and MR safety challenges. CIEDs experiences in an MRI environment are described in the literature. Yet, with the advent of Magnetic Resonance guided Radiotherapy (MRgRT) using hybrid MR and linear accelerators (MR linac) only case reports exist, and clinical experience is lacking. The intent of this survey was to capture the pattern of practice in institutions employing a low-field MR linac in patients with CIEDs and to derive cautious practice recommendations. Materials and Methods The survey consisted of 9 multiple choice and open questions regarding treatment of patients with MRgRT and experiences with different devices with follow-up inquiries and was sent to all worldwide active low-field MR linac centers (n=53). The participants gave information about patients until the end of 2021. Results We received replies from 13 centers worldwide (response rate 25%) which provided data on their decision making process of CIED patients in an MR environment. 54% of the centers had been treating 41 CIED patients in total, while 46% had not yet treated CIED patients but would consider treatment if specific requirements were met. 62% of the centers with CIED experience would allow MR conditional devices, the remaining centers (23%) would also allow non-conditional devices. 2 centers (15%) did not allow any CIED. 95% of the patients had conditional CIEDs and two patients had nonconditional devices. 28 % of all reported devices were CIEDs with cardioverter, defibrillator function (ICDs). The focus of all centers was the benefit of MRgRT vs the risk of device damage or failure. Some centers would only treat if a) the patient was not CIED dependent (15%), b) the device could be turned off (8%), or c) if a continuous heart and O2 monitoring was not needed (8%). The centers developed individual workflows based mainly on technical data sheets, national guidelines and cardiologist’s recommendation and cardiologists periprocedural check. Yet, only one third of the centers implemented a CIED physics specific checklist. Monitoring was in most cases continuous visual and verbal monitoring besides common emergency precautions. Pulse oximetry was the most frequent reported monitoring modality. No CIED related incident has been reported so far. Conclusion Despite missing MRgRT recommendations on the management of CIEDs, half of the responding centers allowed patient treatment with CIED after following safety procedures and weighting benefit risk of MRgRT. No clinical incidence, device damage or change with the 41 patients treated was reported, indicating that MRgRT in CIED patients could be considered safe, given pre—treatment checklists, protocols, and close collaborations with cardiologists. We recommend center manufacturer collaboration and experience expansion of all participating centers in further surveys. PO-1855 Patients with cardiac implantable electronic devices: A Patterns of Care Survey for low-field MRgRT.

PO-1856 Implementation of the DirectDensity CT reconstruction kernel for radiotherapy planning

R. Tulip 1 , S. Manolopoulos 1 , N. Richmond 2 , C. Walker 2

1 Northern Centre for Cancer Care - North Cumbria - Newcastle upon Tyne Hospitals NHS Foundation Trust, Radiotherapy Physics, Carlisle, United Kingdom; 2 Northern Centre for Cancer Care - Newcastle upon Tyne Hospitals NHS Foundation Trust, Radiotherapy Physics, Newcastle-Upon-Tyne, United Kingdom Purpose or Objective The Hounsfeld number–density (HN-D) calibration curve used in planning systems is energy dependent and discontinuous at soft tissue-like densities. Scanning patients at a kVp optimal for image quality requires multiple HN-D curves; increasing quality assurance burdens and adding potential confusion in planning processes. Traditionally HN-D curves are limited to