Room: Exhibit Hall | Forum 2
Purpose: A limiting factor in the treatment of pelvic cancer with radiotherapy and chemotherapy is damage to the bone marrow. Radiation converts hemopoietically active, or â€œredâ€?, bone marrow into inactive â€œyellowâ€? bone marrow. This change is accompanied by an increase in fat from the normal level of 20-40% to 80-95%. The objective of this proposal is to demonstrate the use of quantitative fat imaging for assessing the effects of radiotherapy on bone marrow during treatment.
Methods: It was observed early on that long-term conversion of red to yellow bone marrow can occur after RT. However, MRI techniques have only been considered as quantitative in the past 5 years with the introduction of the Proton Density Fat Fraction (PDFF). The adoption of quantitative MRI into RT has recently become practical by the introduction of on-board MRI of MRgRT systems. A PDFF imaging sequence was implemented on our Viewray MRIdianâ€™s 0.35T magnet with the following parameters: sagittal 2D SPGR, 224x224 matrix over 40cm, TR 150ms, TE 5-25ms (6 echos total), flip angle 30-90 degrees, anterior sat-band to reduce respiratory motion artifact.
Results: We have implemented an imaging protocol to measure PDFF and T1 and have preliminary data on 1 volunteer and 1 patient. Image quality is acceptable for clinical applications at sub-2mm in-plane and 5mm through-plane resolution in scan time of 48 seconds. Our pilot spine PDFF maps on our MRgRTâ€™s 0.35T MRI are comparable in quality to those obtained at 1.5T (slightly reduced resolution and SNR). Mean PDFF values between 1.5T and 0.35T are in reasonable agreement and std dev are similar indicating comparable SNR (supporting document). The patient longitudinal PDFFs show unstable image quality due to machine issue.
Conclusion: PDFF imaging is feasible on the 0.35T MRgRT on-board MRI. It could be a useful functional MRI tool for personalized RT.
Funding Support, Disclosures, and Conflict of Interest: Dr. Yang receives speaking honorarium from Viewray Inc., Dr. Yang serves as short-term consultant for Viewray Inc.