Abstract
BackgroundBefore 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.MethodsForty-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 (D̅image,PVC) with absorbed doses calculated using the method described by the European Association of Nuclear Medicine (pre-therapeutic method; DEANM).ResultsUsing 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: D̅image,PVC = 0.94 × DEANM + 1.35.ConclusionPost-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.
Highlights
Before radioiodine therapy for Graves’ disease, the estimated thyroidabsorbed dose is calculated based on various clinical parameters
Using the European Association of Nuclear Medicine (EANM) guidelines, absorbed dose is determined based on thyroid volume, radioiodine uptake (RIU), and effective iodine half-life
Mean DEANM calculated by EANM-based thyroid dosimetry was 230.2 ± 56.7 Gy
Summary
Before radioiodine therapy for Graves’ disease, the estimated thyroidabsorbed dose is calculated based on various clinical parameters. The actual accumulation of iodine in the thyroid during radioiodine therapy is not determined. The therapeutic effect of radioiodine therapy for Graves’ disease relates to the amount of administered radioactivity, or thyroid-absorbed dose [4, 5]. Using the EANM guidelines, absorbed dose is determined based on thyroid volume, radioiodine uptake (RIU), and effective iodine half-life. The actual accumulation of iodine in the thyroid at the time of radioiodine therapy can only be estimated because these calculations use formulae to determine administered radioactivity before treatment. These formulae assume homogeneous uptake of iodine in the thyroids of patients with Graves’ disease
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
