Endocrine Abstracts

Background: Diagnostic thyroid scans using technetium-99m pertechnetate are widely used to differentiate the causes of hyperthyroidism. Only 1-5% of the administered isotope is taken up by the thyroid after 20 minutes resulting in high background radioactivity.

Objectives: To determine the effective radiation dose and calculated organ doses after a standard administration of Technetium-99m pertechnetate in patients referred for diagnostic scans.

Methods: All patients participating in the study gave their written informed consent. We used SPECT imaging and 2D whole body imaging to determine the radiopharmaceutical retention within regions of specific uptake i.e. thyroid, stomach, bladder, salivary glands. IDAC 2.1 was used to determine effective doses.

Results: The effective dose calculated for the standard 78.4 MBq administration was 4.89 mSv. The highest organ doses expressed as tissue dose per administered activity (mGy/MBq) were observed in the thyroid (0.448) followed by salivary glands (0.018), oesophagus (0.011), bladder wall (0.009), reproductive system (0.007) and lymphatic nodes (0.006). Lowest organ doses were in the lens (0.002) and skin (0.002).

Conclusions: These are preliminary results from the Simplification of Low Level Internal Dosimetry study (SOLLID). As more data are accumulated we hope to develop a simple method of determining tissue doses which will help guide clinicians ordering nuclear medicine scans.