ESTRO 2022 - Abstract Book

S1454

Abstract book

ESTRO 2022

In the LR-CTV, the near-minimum BED(D98%) was comparable between the SEQ and SIB 48.0 ( p = 0.19), while a statistically significant increase was found for SIB 54.4 plans ( p = 0.002). Significant reduction ( p = 0.002) of the median BED(D50%) and near-maximum BED(D2%) was achieved with both SIB dose levels (see Table 2).

Conclusion The SIB technique resulted in highly conformal dose distributions with the reduction of the unintended dose to the LR-CTV. A prescription dose range for the LR-CTV will be clinically defined to offer tailored personalized treatments, according to the clinical and imaging characteristic of the patients.

PO-1656 Accuracy of diffusion-weighted MRI in radiotherapy setup for multicenter PET/MRI in head/neck cancer

R.M. Winter 1 , M. Lium 2 , O. Engelsen 3 , O. Sæther 4 , K.R. Redalen 2

1 Norwegian University of Science and Technology, Department of Physics , Trondheim, Norway; 2 Norwegian University of Science and Technology, Department of Physics, Trondheim, Norway; 3 University Hospital of North Norway (UNN), PET Imaging Center, Tromsø, Norway; 4 St. Olavs hospital, Trondheim University Hospital, Department of Radiology and Nuclear Medicine, Trondheim, Norway Purpose or Objective Diffusion-weighted MRI (DWI) is of growing interest in multicenter imaging biomarker studies. However, using different MR systems in multicenter studies has the drawback that it may increase the variation in the image values. This is especially relevant for PET/MR systems tailored to imaging the patient in radiotherapy position, since the MR coil setups designed to accommodate the patient positioning tools typically have lower signal-to-noise ratio (SNR) which may add even more variation. Our aim was to assess the performance of a radiotherapy tailored PET/MR system for quantitative DWI in a multicenter imaging study in head/neck cancer (EMINENCE, clinicaltrials.gov NCT04612075). Materials and Methods Performance was assessed on a 3T PET/MR system (Siemens) with radiotherapy setup (Medibord; Fig. 1A) in two different centers. DWI was measured in a calibration phantom (High Precision Devices, Inc; Fig. 1B) recommended by the Quantitative Imaging Biomarkers Alliance (QIBA). The ice water cooled phantom contained 13 vials of different mediums to allow the measurement of six known apparent diffusion coefficients (ADC). For a set of four scans the QIBA benchmark protocol (SS- EPI; four b-values; 0, 500, 900, 2000 s/mm 2 ; 1 average each; transverse acquisition) was used. Scans were repeated three times using the same protocol but with increasing number of averages (2; 3; 2,2,3,5) to account for the reduced SNR in radiotherapy setup and investigate possible improvements in ADC accuracy. SNR of the b0 image, ADC bias ( Δ ADC, measured minus true value), %bias, precision (coefficient of variation, CV), short-term repeatability (within-subject CV, wCV) and intercenter reproducibility (iCV) were analyzed according to the QIBA profile. Measurements were repeated with a diagnostic 16 channel coil (16ch) for comparison. A clinical protocol for low distortion DWI (RESOLVE) was tested in center 1.