Abstract
Data that have been used in almost all MIRD S value absorbed dose and effective dose calculations to date have been based upon stylized anatomic computational phantoms and tissue weighting factors adopted by the ICRP in its Publication 60. Recently, more anatomically realistic phantoms have become available, which are likely to provide more accurate effective dose values for diagnostic agents. Gallium-68-DOTATATE is a radiolabeled somatostatin analog that binds with high affinity to somatostatin receptors, which are over-expressed in neuroendocrine tumors, and can be used for diagnostic PET/CT-based imaging. Several studies have reported effective dose values for 68Ga-DOTATATE using the 1987 Cristy-Eckerman stylized phantoms (CEP); here we present effective dose calculations using both the ICRP 60 and more updated formalisms. Methods: Whole-body PET/CT scans were acquired for 16 patients after 68Ga-DOTATATE administration. Contours were drawn on the CT-images for spleen, liver, kidneys, adrenal glands, brain, heart, lungs, thyroid gland, salivary glands, testes, red marrow (L1–L5), muscle (right thigh) and whole-body. Dosimetric calculations were performed based on the CEP and the more recent ICRP 110 reference voxel phantoms. Tissue weighting factors from ICRP 60 were used for the CEP effective dose calculations and tissue weighting factors from ICRP 103 for the ICRP 110 phantom calculations, respectively. Results: The highest computed organ absorbed dose coefficients were, in descending order, to the spleen, pituitary gland, kidneys, adrenal glands and liver. The effective dose was 0.023±0.003 mSv/MBq using ICRP 110 phantoms with tissue weighting factors from ICRP 103, which was significantly lower than 0.027±0.005 mSv/MBq calculated using CEP with tissue weighting factors from ICRP 60. One of the largest differences in absorbed dose coefficient estimates was for the urinary bladder wall 0.040±0.011 mGy/MBq (ICRP 110) compared to 0.090±0.032 mGy/MBq (CEP). Conclusion: This study shows that the effective dose is slightly overestimated using CEP compared to the ICRP 110 phantoms in combination with the latest tissue weighting factors from ICRP 103. The more detailed handling of electron transport in the latest phantom calculations gives significant differences in estimates of the absorbed dose to stem cell targeted in for the walled organs of the alimentary tract.
- PET/CT
- Radiobiology/Dosimetry
- Radiopharmaceuticals
- Gallium-68-DOTATATE
- PET/CT-imaging
- dosimetry
- effective dose
- normal tissue
- Copyright © 2018 by the Society of Nuclear Medicine and Molecular Imaging, Inc.