A thermoluminescent method for the evaluation of the ${}^{131}$I effective half-life in the thyroid when treating Graves' disease

When planning treatment for Graves' disease with ${}^{131}$I, the effective half-life (T${}_{eff}$) should be estimated individually as it depends on biological characteristics such as iodine uptake and excretion, which differ from an individual to another (Berg et al. 1996). All the methods to quantify T${}_{eff}$ described in the literature are quite complex and are difficult to be used in clinical routine. With the aim of optimizing this process, a simplified method is proposed here to evaluate T${}_{eff}$ of ${}^{131}$I during treatment of Graves' disease. The present study suggests improving the method of determining T${}_{eff}$ based on thermoluminescence dosimetry. This involves implementing a new method and includes reduction of TLD (Thermoluminescent Dosimeter) measurements. The proposed method was validated on patients with Graves' disease. The radiation dose delivered to the patients was determined using the MIRD (Medical Internal Radiation Dosimetry) formalism. The relative difference between T${}_{eff}$ obtained based on seven measurement intervals at [0–24 h, 24–48 h, 48–72 h, 72–96 h, 96–120 h, 120–144 h, 144–168 h] and based on three measurement intervals at [0–24 h, 72–96 h, 144–168 h] and [0–24 h, 120–144 h, 144–168 h] was 1.9% and 3.81%, respectively. Comparison of doses obtained based on a general T${}_{eff}$ and on a personalized T${}_{eff}$ gave a statistically significant difference with a correlation coefficient R${}^2$ of 0.44. The T${}_{eff}$ obtained from just three measurements was found to be sufficiently accurate and easily applicable. The results obtained demonstrate the need to determine and use personalized T${}_{eff}$ values instead of using a fixed value of 7 days.