[Lungs absorbed dose in radioiodine therapy of differentiated thyroid carcinoma with diffuse pulmonary metastases]

The objective of this work was to estimate the absorbed dose of 131I to lungs in 131I therapy of differentiated thyroid carcinoma(DTC) with diffuse pulmonary metastases. Ten DTC patients with diffuse pulmonary metastases were recruited prospectively. Whole body planar scintigrams were acquired serially after administration of 7.4 GBq 131I to patients. The counts from the regions of interest of lungs and total body were obtained and converted to the percent of administered activity. The time-activity curves of lungs and total body were fit, and the areas under the curves were calculated. It was assumed that beta-eletron emissions from 131I deposited in lungs were completely absorbed by the diffuse DTC metastatic lesions, and that gamma-photon emissions from 131I deposited in the lungs and the remainder of body were irradiating the lungs. The absorbed dose to lungs was calculated according to Medical Internal Radiation Dosimetry (MIRD) formula. The median lungs absorbed dose was 0.33 Gy (range, 0.22-8.21 Gy). Based on the empiric fixed activity therapy of DTC with diffuse pulmonary metastases,the absorbed dose to lungs is low.