Purpose: Predictive 3-dimensional dosimetry requires spatial concordance between diagnostic and therapeutic activity distributions. We assess similarity between theranostic pairs (99mTc–macroaggregated albumin [MAA] single photon emission computed tomography [SPECT] and 90Y microsphere positron emission tomography [PET]) in patients using criteria that account for spatial resolution differences and misregistration. Methods and Materials: Phantom-based acceptance criteria were determined using a liver phantom filled with 99mTc and 90YCl3 and scanned with SPECT/computed tomography [CT] and PET/CT, respectively. Gaussian blurring was applied to PET to match 99mTc phantom scan image quality. After rigid registration between SPECT/CT and PET/CT, perturbations up to ±3 voxels were applied to determine the similarity metric (SM) sensitivity. 99mTc-MAA SPECT/CT and 90Y microsphere PET/CT image pairs/patients (n = 23) were processed analogously. SMs calculated included the Pearson correlation coefficient (ρr), Lin's concordance correlation coefficient (ρc), Spearman's rank correlation coefficient (ρs), the mean squared difference, and the Dice similarity coefficient (DSC). Patient-specific acceptance criteria were determined by evaluating the SMs of the blurred PET compared with itself misregistered. Results: After transforming PET to SPECT resolution, high similarity was found in phantom, with ρc, ρr, ρs > 0.98 ± 0.01, a mean squared difference of (4.1 ± 0.3) × 10−4 and DSC > 0.85 ± 0.01 for investigated thresholds (5%, 30%, and 50%). SMs for patients varied from poor to good. A small percentage (13%-30%) of patient scans were acceptable using phantom-based acceptance criteria. The percentage increased slightly (17%-35%) using patient-specific acceptance criteria. DSC for most patients were substantially lower (average 0.95 vs 0.61 for 5% threshold) than phantom values. Conclusions: At best, 35% of patients had an SM within the acceptance criteria established to account for imaging-related effects impacting spatial concordance between 99mTc-MAA SPECT and 90Y PET. Additional clinical factors should be evaluated in the future. The procedure of accounting for image-related effects when assessing spatial concordance can be applied to other theranostic pairs.
|Number of pages||8|
|Journal||International Journal of Radiation Oncology Biology Physics|
|State||Published - Aug 1 2019|