Investigation of post-therapeutic image-based thyroid dosimetry using quantitative SPECT/CT, iodine biokinetics, and the MIRD’s voxel S values in Graves’ disease

• Published in: EJNMMI physics Vol. 7; no. 1; p. 6
• Main Authors: Fujita, Naotoshi, Koshiba, Yumiko, Abe, Shinji, Kato, Katsuhiko
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 28.01.2020; Springer Nature B.V; SpringerOpen
• Subjects: Absorbed dose; Accumulation; Activity coefficients; Applied and Technical Physics; Computational Mathematics and Numerical Analysis; Computed tomography; Correlation coefficients; Dosimeters; Dosimetry; Engineering; Graves’ disease; Image acquisition; Imaging; Internal radionuclide dosimetry; Iodine; Iodine 131; Mathematical analysis; Medical imaging; Medicine; Medicine & Public Health; Nuclear Medicine; Original Research; Photon emission; Radiation dosage; Radioiodine therapy; Radiology; Regression analysis; SPECT/CT; Therapy; Thyroid; Thyroid gland; Tomography; Absorbed dose; Graves’ disease; Radioiodine therapy; SPECT/CT; Internal radionuclide dosimetry; Thyroid
• ISSN: 2197-7364; 2197-7364
• DOI: 10.1186/s40658-020-0274-7

Background Before radioiodine therapy for Graves’ disease, the estimated thyroid-absorbed dose is calculated based on various clinical parameters. However, the actual accumulation of iodine in the thyroid during radioiodine therapy is not determined. We validated the feasibility of post-therapeutic image-based thyroid dosimetry through quantitative single-photon emission computed tomography (SPECT) imaging and thyroid biokinetics and expanding the Medical Internal Radiation Dose Committee’s (MIRD) voxel dosimetry guidelines. Methods Forty-three patients with Graves’ disease who underwent radioiodine therapy were chosen as subjects for this retrospective analysis. We acquired patients’ SPECT images 24 h after oral administration. SPECT images were quantified using system volume sensitivity to calculate time-integrated activity coefficients on a voxel basis. Absorbed dose was obtained by convolving MIRD guideline voxel S values with time-integrated activity coefficients. To determine accuracy, we compared the results obtained using the post-therapeutic image-based absorbed-dose method ( D̅ image,PVC ) with absorbed doses calculated using the method described by the European Association of Nuclear Medicine (pre-therapeutic method; D EANM ). Results Using image-based dosimetry as post-therapeutic dosimetry, we visualized the local accumulation and absorbed dose distribution of iodine in the thyroid. Furthermore, we determined a strong correlation (Pearson’s correlation coefficient = 0.89) between both dosimetries, using the regression equation: D̅ image,PVC  = 0.94 ×  D EANM  + 1.35. Conclusion Post-therapeutic image-based doses absorbed in the thyroid resembled those of pre-therapeutic EANM method-based absorbed doses. Additionally, the post-therapeutic image-based method had the advantage of visualizing thyroid iodine distribution, thus determining local dose distributions at the time of treatment. From these points, we propose that post-therapeutic image-based dosimetry could provide an alternative to standard pre-therapeutic dosimetry to evaluate dose response.