Personalised assessment of the dose following radioiodine remnant ablation for a patient presenting a residual intrathoracic goitre

摘要

A patient treated with 3.7 GBq of I-131 after thyroidectomy for a papillary carcinoma presented, three days after iodine administration, an unusually elevated dose rate at 1 m. Scintigraphy and Single Photon Emission Computed Tomography coupled with Computed Tomography (SPECT/CT) were performed and showed a significant iodine uptake at the anterior mediastinal level due to the presence of a residual intrathoracic goitre. The proximity between this iodofixant goitre and the surrounding tissues prompted dose estimations to local organs at risk, in particular the heart. Dosimetric estimations were initially performed with OLINDA/EXM software, commonly used in nuclear medicine. More personalised doses were then calculated using the OEDIPE software associated with the Monte Carlo code MCNPX. Calculations with the OLINDA/EXM software enabled a first assessment of the mean absorbed dose to the heart, estimated at about 2 Gy for an uptake of 56% of the administered activity. In a second step, the use of the OEDIPE software allowed us to take into account the specific geometry of the patient as well as the distribution of iodine uptake at a mediastinal level and to determine a mean absorbed dose of approximately 1 Gy to the heart. Thus, the use of a voxelised phantom based on CT images of the patient, associated with direct Monte Carlo calculations, enabled us to improve the calculation of the absorbed doses to the heart compared with the use of a standard anthropomorphic phantom.