Research on multi-sized phantoms for thyroid counting calibration

Objective: In order to improve the accuracy of thyroid counter measurement for radioiodine (such as ¹³¹I) ingested by large amounts of public, multi-sized phantoms for thyroid counting calibration were studied. Method: Firstly, multi-sized neck (thyroid) phantoms corresponding to 1 ∼ 15-year-old children, adolescents and adults were designed according to the data of Chinese reference adult male voxel (CRAM) model, neck size and thyroid mass in different age groups population, and these phantoms included the main organs and tissues of the human neck, such as the thyroid, trachea, esophagus, cervical spine, and bone marrow. Then the Monte Carlo method was used to simulate the detection efficiency response of the NaI (Tl) type thyroid counter to phantoms with different types and sizes. Result: When the measurement distance was 20 cm, the relative biases of thyroid counter detection efficiency for IAEA/ANSI neck phantom, CRAM-neck phantom and the adult male neck phantom (TM) were less than 2%, but the relative biases of detection efficiency for different sized neck phantoms were 1% ∼ 30%. Conclusion The adult male neck phantom (TM) and IAEA/ANSI neck phantom are equivalent as the measurement distance was 20 cm, and the difference in the size of the calibration phantoms has a big influence on the detection efficiency of thyroid counters. Therefore, it is of great significance for improving the accuracy of measurement to develop neck (thyroid) phantoms corresponding to all age groups, especially for children. (authors)