Biodistribution, pharmacokinetics, and organ-level dosimetry for 188Re-AHDD-Lipiodol radioembolization based on quantitative post-treatment SPECT/CT scans

BackgroundRhenium-188-labelled-Lipiodol radioembolization is a safe and cost-effective treatment for primary liver cancer. In order to determine correlations between treatment doses and patient response to therapy, accurate patient-specific dosimetry is required. Up to date, the reported dosimetry of Re-188-Lipiodol has been based on whole-body (WB) planar imaging only, which has limited quantitative accuracy. The aim of the present study is to determine the in vivo pharmacokinetics, bio-distribution, and organ-level dosimetry of Re-188-AHDD-Lipiodol radioembolization using a combination of post-treatment planar and quantitative SPECT/CT images. Furthermore, based on the analysis of the pharmacokinetic data, a practical and relatively simple imaging and dosimetry method that could be implemented in clinics for Re-188-AHDD-Lipiodol radioembolization is proposed.Thirteen patients with histologically proven hepatocellular carcinoma underwent Re-188-AHDD-Lipiodol radioembolization. A series of 2-3 WB planar images and one SPECT/CT scan were acquired over 48h after the treatment. The time-integrated activity coefficients (TIACs, also known as residence-times) and absorbed doses of tumors and organs at risk (OARs) were determined using a hybrid WB/SPECT imaging method.ResultsWhole-body imaging showed that Re-188-AHDD-Lipiodol accumulated mostly in the tumor and liver tissue but a non-negligible amount of the pharmaceutical was also observed in the stomach, lungs, salivary glands, spleen, kidneys, and urinary bladder. On average, the measured effective half-life of Re-188-AHDD-Lipiodol was 12.51.9h in tumor. The effective half-life in the liver and lungs (the two organs at risk) was 12.61.7h and 12.0 +/- 1.9h, respectively. The presence of Re-188 in other organs was probably due to the chemical separation and subsequent release of the free radionuclide from Lipiodol. The average doses per injected activity in the tumor, liver, and lungs were 23.5 +/- 40.8mGy/MBq, 2.12 +/- 1.78mGy/MBq, and 0.11 +/- 0.05mGy/MBq, respectively. The proposed imaging and dosimetry method, consisting of a single SPECT/CT for activity determination followed by Re-188-AHDD-Lipiodol clearance with the liver effective half-life of 12.6h, resulted in TIACs estimates (and hence, doses) mostly within +/- 20% from the reference TIACs (estimated using three WB images and one SPECT/CT).ConclusionsThe large inter-patient variability of the absorbed doses in tumors and normal tissue in Re-188-HDD-Lipiodol radioembolization patients emphasizes the importance of patient-specific dosimetry calculations based on quantitative post-treatment SPECT/CT imaging.