ESTRO 2023 - Abstract Book

S1855

Digital Posters

ESTRO 2023

Conclusion The MR-Sim achieved conformance certification to the QIBA DWI profile, providing confidence in the use of ADC as a biomarker. In additional, it was seen that room temperature calibration to traceable reference values is possible and allows simple routine QA with minimal preparation, at more clinically-relevant ADC values and reduced artefacts. However, temperature uncertainties are greater. QIBA tolerances specified for 0°C water generally provide a good baseline for room temperature tolerances. [1] K. E. Keenan et al., "MRI-visible liquid crystal thermometer," Magnetic Resonance in Medicine, vol. 84, no. 3, pp. 1552-1563, 2020. [2] P. S. Tofts et al., "Test liquids for quantitative MRI measurements of self-diffusion coefficient in vivo," Magnetic Resonance in Medicine, vol. 43, no. 3, pp. 368-374, 2000. 1 The Christie NHS Foundation Trust, CMPE, Manchester, United Kingdom; 2 The Christie NHS Foundation Trust, Radiotherapy Services, Manchester, United Kingdom; 3 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom; 4 The Christie NHS Foundation Trust, Research and Innovation, Manchester, United Kingdom Purpose or Objective The MR Linac Consortium biomarkers working group Prostate DWI sequence was used to measure median prostate ADC in the prostate of patients undergoing treatment on the MR Linac (MRL). The sequence suffered from poor SNR and resolution which limited clinical value. The aim of this work was to improve image quality without compromising the quantitative utility of the sequence and maintaining a reasonable acquisition time. Materials and Methods The consortium sequence (SS-EPI DWI, b = 0, 150, 500 s/mm2 (2, 4, 16 averages respectively), TE/TR = 82/3354 ms, voxel = 1.9x1.9x4.0 mm, Averages = 1, TA = 3:31) was modified to improve in-plane resolution and increase SNR (SS-EPI DWI, b = 150, 500 s/mm2 (5, 12 averages respectively), TE/TR = 70/2800 ms, voxel = 1.4x1.4x5.0 mm2, Averages = 2, TA = 4:48). The b = 0 image was removed as it is not used to calculate the ADC map. Additional averages were added to the b = 150 and 500 s/mm2 images to improve SNR. Thirteen patients treated on the MRL, recruited to the MOMENTUM study, were scanned with both sequences at their MR planning session. Visual image quality assessment of the DWI images and ADC maps was undertaken by a radiologist who assessed the appearance of the whole prostate, transitional/peripheral zones (TZ/PZ), tumour and seminal vesicles against the MOMENTUM image quality assessment criteria (1 = not scanned, 2 = not visible, 3 = not clear, 4 = clear, 5 = very clear), while blinded to the sequence used. ADC maps (figure 1) were calculated using the b = 150 and 500 s/mm2 images. Structure contours were obtained by rigidly registering the DWI images to the planning MR images, and adapting the contours drawn on the planning MR. Median whole prostate ADC measurements were compared between the two sequences by Bland-Altmann analysis. PO-2075 Optimising the MRL Consortium Biomarkers Group Prostate DWI Sequence Image Quality & ADC Comparison C. Moore 1 , A. Clough 2 , C. Nelder 2 , C. Eccles 2 , P. Hoskin 3 , R. Chuter 1 , J. Zhong 3 , D. McHugh 1 , A. Choudhury 4 , M. Dubec 1