Page 191 - Quantitative Imaging of Small Tumours with Positron Emission Tomography
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Chapter 9 Methods The patient underwent whole body PET-CT imaging on a time-of-flight scanner for both [18F]DCFPyL and [18F]FDHT. Injected dosages of [18F]DCFPyL at baseline and follow-up were 316 MBq and 303 Mbq, with uptake intervals of 124 min and 133 min, respectively. Injected dosages of [18F]FDHT were 232 MBq and 238 Mbq, with uptake intervals of 45 min and 45 min, respectively. For [18F]DCFPyL, we delineated the total tumour burden using a PERCIST SUV threshold based on liver uptake (9), which is a feasible approach due to the high tumour-to-background contrast and stable liver uptake between patients. Due to the unfavorable biodistribution of [18F] FDHT, an alternative approach was needed. Therefore, the total tumour burden was delineated using a bone-mask (CT-based) where all uptake with SUV >1.9 was included (10). Next, nodal metastases and bone marrow disease was manually delineated. On each scan, we measured the PSMA- or FDHT-positive tumour volume, SUVmean, the Tumour-to-Blood ratio (TBR), and the total lesion uptake for SUV and TBR (SUV/TBR multiplied by the total tumour volume). Also, we measured the SUVmean in normal tissues: blood, kidneys, parotid glands, spleen, and liver for [18F]DCFPyL; blood, kidneys, spleen, muscle, and liver for [18F]FDHT. Then, we calculated the relative differences in those measures between the baseline and follow-up PET-CT scans. As prostate cancer metastases are often very small, we also quantified the total tumour burden using images that were corrected for partial-volume effects using post-reconstruction iterative deconvolution that was calibrated to comply with updated EARL2 guidelines. ab 0 400 300 200 100 0 -60 -100 Original PVC -20 -40 Figure 9.2: Changes in [18F]DCFPyL uptake of (A) normal tissues and (B) the total tumor burden, from the scans shown in Figure 9.1. Changes in normal tissue uptake pertain to SUVmean. The whole body tumor metrics were derived from the total tumor burden as a single VOI. PVC = partial-volume correction. 190 Relative change (%) Relative change (%) Bloodpool Liver Spleen Parotid gland (left) Parotid gland (right) Kidney (left) Kidney (right) SUVmean TBR Volume Total-lesion-uptake SUV Total-lesion-uptake TBR