ESTRO 2021 Abstract Book

S588

ESTRO 2021

intra-patient variation was observed in the kidney, where renal parenchyma and calyx were included in the contours. The average inter-patient variation over all organs was 1.2%, highlighting the potential benefit of considering variation in tissue parameters instead of using tabulated mean values. For brain, lens, liver and urine the ICRU46 values are within the determined 2SD_inter interval around the respective mean value, while for prostate and kidney the ICRU46 values are outside this interval. For kidney, cohort mean SPR was 2.3% below ICRU46. Conclusion Radiological tissue parameters in the head and pelvis were characterised in-vivo in a large patient cohort using dual-energy CT. This substantially expands and reassesses the current standard database defined in ICRU46 by smaller substructures in the brain as well as by the quantification of organ-specific inter- and intra-patient variation. Our results can be used as input to simulate intra- and inter-patient variability e.g. in Monte Carlo simulations.

PD-0757 Low dose cone beam CT for paediatric image-guided radiotherapy: how much dose is enough? A. Bryce-Atkinson 1 , R. De Jong 2 , T. Marchant 3 , G. Whitfield 4,5 , M.C. Aznar 1 , A. Bel 2 , M. van Herk 1 1 The University of Manchester, Division of Cancer Sciences, Faculty of Biology Medicine and Health, Manchester, United Kingdom; 2 Amsterdam University Medical Center, Department of Radiation Oncology, Amsterdam, The Netherlands; 3 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom; 4 The Christie NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, United Kingdom; 5 Royal Manchester Children's Hospital, The Children's Brain Tumour Research Network, The University of Manchester, Manchester, United Kingdom