ESTRO 2023 - Abstract Book

S471

Sunday 14 May 2023

ESTRO 2023

Results The various calibration methods showed a larger variation in calibration factors on the MR-linac relative to a conventional linac. The results of basic characterization tests are shown in Table 1. PDD showed good correspondence with the microDiamond detector. The response of the detector was influenced by the orientation of the detector relative to the magnetic field up to 10.7%.

Plan QA showed similar results for the PSD and Semiflex measurement with a dose difference of 0.6%. The dose differences with and without MRI acquisitions are plotted in Figure 1. Relative dose differences and standard deviations were 0.6±0.9% and 0.2±1.1%, respectively, for with and without MRI acquisition relative to the Semiflex measurement.

Conclusion Basic performance of the Blue Physics PSD has been tested and shown to be suitable for relative dosimetry in the MR-linac. The calibration methods showed variation and need to be further investigated. Furthermore the detector is dependent on the orientation relative to the magnetic field. No significant difference in dose measurements with and without MRI acquisition were observed. Further investigation is needed to qualify as an absolute dosimeter for the MR-linac.

Proffered Papers: Patient perspectives

OC-0589 Barriers for inclusion in a proton therapy trial among Danish patients with head and neck cancer A. Kristensen 1 , J. Friborg 2 , K. Jensen 3 , J.G. Eriksen 4 , C. Maare 5 , M. Farhadi 6 , J. Johansen 7 , C.R. Hansen 7 , M. Andersen 8 , S. Dalton 9 , C. Grau 3 1 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus , Denmark; 2 Rigshospitalet, Department of Oncology, Copenhagen , Denmark; 3 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 4 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 5 Herlev Hospital, Department of Oncology, Herlev, Denmark; 6 Zealand Hospital, Department of Oncology, Naestved, Denmark; 7 Odense University Hospital, Department of Oncology, Odense, Denmark; 8 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; 9 Danish Cancer Society Research Center, Survivorship & Inequality in Cancer, Copenhagen, Denmark Purpose or Objective In Denmark proton therapy (PT) is offered in one centralised treatment facility and for patients with head and neck cancer (HNC) only by participating in a randomized trial. Candidates for this trial are identified in a model-based selection procedure where treatment plans with photons and protons are compared. Normal tissue complication probability (NTCP) are used as a biomarker for expected benefit of PT.