ESTRO 2023 - Abstract Book

S804

Monday 15 May 2023

ESTRO 2023

V-maps with the average V-signal within a selected ROI and therefore eliminates the dependency on the signal amplitude. Six different ROI locations within the lung have been investigated. Results Due to a clear signal variation with frequencies corresponding to the breathing frequency and the heart beat, the NuFD algorithm was successfully applied to all volunteer scans and V- and Q-maps were generated. Comparing the normalization results of all volunteer scans (Fig. 1 and Tab. 1), median deviations of 7.8%/7.0%/12.3% (normalization factor/best ROI/worst ROI) from the reference scan were achieved for combined slices, which outperforms the uncorrected median deviation of 32.4%.

Conclusion Non-contrast enhanced functional lung MRI concepts can be transferred to a 0.35 T MR-Linac and integrated into clinical treatment workflows with standard equipment and short acquisitions. For the comparison of intra-volunteer scans, two signal normalization strategies have been successfully introduced and demonstrated comparable performance. MO-0956 Time evolved hypoxia guided proton therapy dose painting in HNSCC patients S. Makkar 1,2 , A. Bogaert 1 , B. Bachtiary 1 , C. De Angelis 3 , C.M. Zegers 4 , E. Roelofs 4 , K. McNamara 1,2 , J. Hrbacek 1 , D.C. Weber 3,5,6 , A. Lomax 1,2 , C. Winterhalter 1,2 1 Paul Scherrer Institute, Center for Proton Therapy, Villigen, Switzerland; 2 ETH Zürich, Department of Physics, Zürich, Switzerland; 3 Paul Scherrer Insitute, Center for Proton Therapy, Villigen, Switzerland; 4 GROW School for Oncology, Maastricht University Medical Centre+, Department of Radiation Oncology (Maastro), Maastricht, The Netherlands; 5 University Hospital of Zurich, Department of Radiation Oncology, Zürich, Switzerland; 6 Inselspital, Bern University Hospital, University of Bern, Department of Radiation Oncology, Bern, Switzerland Purpose or Objective Tumour hypoxia causes radio resistance therefore, boosting the dose to hypoxic regions in the tumour can help improve the tumour control. We use baseline and in-treatment HX4 PET images to prepare dose escalated proton plans and compare them to the delivered photon plans in patients with head and neck cancer. We design a patient specific workflow for estimating the dose escalation necessary and use it to assess the potential of personalized and time adapted proton plans. Materials and Methods HX4-PET images are used to delineate a hypoxic volume within the clinical target volume (CTV) with a tumour-to-muscle ratio > 1.4. A non-linear conversion model is used to obtain voxelised partial oxygen pressure (pO2), which along with variable linear energy transfer (LETd), is used for the proton-based oxygen enhancement ratio (OER) calculation. The