Dosimetry in differentiated thyroid carcinoma (12-1402R)

Area of Science:

• Nuclear Medicine
• Oncology
• Radiological Physics

Background:

• Differentiated thyroid cancer (DTC) treatment often involves radioactive iodine ((131)I) therapy.
• Accurate dosimetry is crucial for optimizing treatment efficacy and minimizing side effects.
• Establishing a dose-effect correlation in (131)I therapy for DTC remains a clinical challenge.

Purpose of the Study:

• To conduct a dosimetric study of (131)I treatments for differentiated thyroid cancer (DTC) at our institution.
• To investigate potential dose-effect correlations in DTC patients treated with (131)I.
• To evaluate absorbed doses to thyroid bed remnants and the whole body.

Main Methods:

• Thirty DTC patients received 3700 MBq of (131)I and were hospitalized for two nights for radiological protection.
• Dose rates were measured at 1 meter from patients at approximately 20 and 44 hours post-administration.
• Whole-body scans were performed, and a two-compartment model was used to calculate cumulated activities and absorbed doses using the MIRDOSE method.

Main Results:

• Absorbed doses to thyroid bed remnants varied widely (13-1161 Gy) and correlated with dose rate, cumulated activity, and uptake.
• Whole-body absorbed doses ranged from 0.12 to 0.23 Gy.
• All patients achieved successful ablation, irrespective of the wide range of absorbed doses to the thyroid bed remnants.

Conclusions:

• A definitive dose-effect correlation for (131)I therapy in DTC could not be established in this study.
• Successful ablation occurred even with absorbed doses below previously published thresholds.
• Predosimetry for calculating (131)I activity in DTC treatment presents significant challenges.