Radioprotection de l'entourage des patients traités à l'iode 131 pour des cancers différenciés de la thyroïde : comparaison de deux méthodes d'estimation des temps de restriction de contact

In France, it is required to give patients some written radiation safety advice following an iodine-131 therapy of thyroid. However, there is no regulatory methodology proposed to assess the restriction times required to limit radiation dose received by their family and by third persons. In this study, we compared two methods to perform the calculation of restriction times for differentiated thyroid cancer: the first one, called Global method, follows general recommendations and the second one, called PaDe method, provides customized recommendations based on the effective half-life measured for each patient during the 48 h of hospitalization. For these simulations, the input parameters for both methods were dose constraints, contact patterns, final dose rate measurement at discharge of the patient, effective half-life and dose rate variation with distance. For the Global method, these parameters were set and were not changed. For the PaDe method, the effective half-life and the final dose rate were adjusted for each patient. Comparison between the two methods was carried out for 103 patients. For 68.0 % of the patients, no restrictions were necessary according to the PaDe method whereas the Global method required restrictions to be applied during up to 2 days. For almost 16.5 % of them, restriction times estimated with the PaDe method were systematically lower. For the remaining 15.5 %, at least one contact pattern restriction had to be increased according to the PaDe method. Furthermore, with the Global method, the same instructions were given to 97.0 % of the patients. These results showed the limits of the Global method which does not consider individually tailored biological data. Eventually, the use of the personalized PaDe method optimizes the radiation protection by improving the well being of the patient or reinforcing the family and third person's protection.