The Environmental Dose Measurements of High Dose Iodine-131 Treated Thyroid Cancer Patients during Hospitalization Period

Radioiodine mostly 131I is one of the oldest clinical radionuclide types which used widely spread in diagnosis and currently used in the treatment of both thyreotoxicosis and thyroid cancer. This is an integral part of differentiated thyroid carcinoma therapy [1,2]. For most thyroid cancer treatments, large doses of 131I are administered to ablate residual thyroid tissue and functional metastases from thyroid cancer. The success of thyroid ablation with 131I depends mainly on the mass of remaining thyroid tissue in the neck and the initial dose rate to this tissue [3]. The activity to be used for radioiodine therapy still remains subject to discussion at differentiated thyroid cancer (DTC) for ablation of postsurgical thyroid remnants, destruction of metastases and etc. While it is performed by either administering an empiric fixed dose or using dosemetry-guided activities [3]. There is a broad range of the conventional fixed activities of 131I recommended to be administered [4,5]. Normally, the activity is limited for safety reasons to around 7.4 GBq [6]. A summary on the use of fixed activities for the treatment of DTC can be found in a review articles [7-9]. The lesion-based dosemetry concept, mainly on the data of Maxon et al. [10,11], aims at improving the efficacy of the treatment by achieving an absorbed dose threshold of more than 300 Gy to remnants. Because of radiation safety considerations, application of large doses of 131I greater than 800 MBq requires patient hospitalization [12,13]. Most of the administered radioiodine not taken up by thyroid tissue will be excreted from the patient primarily by the kidneys, and consequently, the patient should be encouraged to drink freely to minimize dose to kidneys, bladder and gonads. So, a great majority of the administered activity will appear in the urine [2]. For most patients, 35%-75% of the administered dose is excreted within the first 24 h after dose administration [13,14]. The next most significant pathway is saliva. This will manifest in contamination of eating and drinking utensils, and pillow coverings (due to saliva excretion during sleep). Lesser pathways are sweat and faeces. The proportion of each (apart from urine) will vary widely [2]. Radiation contamination could be expected from patient’s urine, perspiration and saliva over the course of the isolation period. For this reason, patients should be considered as a potential source of radiation contamination, especially during the first 48 hours following administration [2]. When considering radiation safety precautions for attending personnel, members of the general public and patients in adjacent rooms, it is important to remember that 131I emits both negative β particles and prominent gamma photons. Iodine-131 is typical of a complex beta decay scheme with physical half-life of 8.05 days. There are five Volume 1 Issue 2 2016