Room: Track 2
Purpose: To assess the ability of MR and dual energy CT (DECT) imaging to detect radiation-induced bone-marrow changes in a swine model, using ¹8F-fluorothymidine (FLT) PET as the reference standard.
Methods: A Wisconsin Miniature SwineTM underwent simultaneous FLT PET/MR imaging on a GE Signa scanner and Dual Spiral and Rapid kV Switching DECT imaging on a Siemens SOMATOM Definition Edge and a GE Discovery CT750HD scanner, respectively. The PET/MR imaging protocol included whole-body PET acquisition and IDEAL-IQ imaging to generate proton density fat fraction maps. The DECT scans produced vendor-specific images that allow bone-marrow assessment through calcium subtraction. Radiation was delivered using the Viewray MRIdian treatment system to active bone-marrow volumes in the lower-lumbar/upper-sacral spine as identified on the PET images. PET/MR and DECT imaging was repeated at one- and four-weeks post-radiation. To assess bone-marrow changes, regions of interest (ROIs) were placed on the irradiated and unirradiated vertebrae to measure standardized uptake value (SUVmax) on PET, fat fraction on MR, and HU/water concentration on DECT images.
Results: SUVmax in the irradiated vertebrae decreased by an average of 86% at one-week post-radiation and remained at that level at four weeks. Irradiated vertebrae demonstrated an average increase in MR fat-fraction of 25% and 100% at one- and four-weeks post-irradiation, respectively. DECT on both platforms showed decreased bone-marrow activity in the irradiated vertebrae but showed larger variation within the ROIs compared to the MR and PET images.
Conclusion: All imaging modalities investigated here showed potential for assessing changes in marrow following irradiation. PET and MR images showed clear decreases in bone marrow activity in the irradiated areas. While DECT results were in general agreement with the PET and MR results, they demonstrated larger variations that may present challenges for prospective assessments.