Age-dependent exposure to radioactive iodine (131I) in the thyroid and total body of newborn, pubertal and adult fischer 344 rats

Effective half life of iodine for five thyroidectomy patients using an in vivo gamma camera approach

The effective half-life of radioactive iodine for (near) thyroidectomy patients was evaluated using an in vivo gamma camera approach. Five patients with post administered iodine for remnant ablation of thyroid were thoroughly scanned in vivo for one to four weeks. Derived data were analyzed in a MATLAB program to revise the ICRP recommended effective half-life and, thus, to offer a more reliable dose predication protocol from a health physics viewpoint. A quantitative index, AT (Agreement), was also introduced to specify the deviation between the actual measurement and the results fitted in MATLAB for each patient. The ATs were evaluated as 1.52 +/- 1.54 and 14.05 +/- 11.01 for the thyroid compartment and the remainder, re-spectively, indicating a slight discrepancy between the computed and practical results for the remainder. The actual effective half-life of iodine in the thyroid or the body fluid compartment shifted from 7.3d or 0.24 d to only 0.61 +/- 0.50 d or 0.49 +/- 0.23 d, respectively. Additionally, the integrated T(eff) for the remainder (both body fluid and whole body compartments) was still about 5.8d, since the body fluid and the whole body compartment was inseparable in real whole body scanning. The branching ratio from body fluid compartment to the thyroid and the excretion compartment also changed from 30% and 70% to 11.6 +/- 14.0% and 88.4 +/- 14.6%, respectively. The thyroid was the dominant compartment for a healthy person in the traditional biokinetic model. However, this dominant compartment was shifted to both thyroid and body fluid, based on analyses of the data following thyroidectomy, for the patients herein.

Endocrine intervention during irradiation does not prevent damage to the thyroid gland

Radiation to the head-neck region may damage the thyroid gland, leading to hypothyroidism or thyroid carcinoma. Outcomes of radiation protection by lowering plasma thyroid-stimulating hormone (TSH) have thus far been ambiguous. Our aim was to evaluate the radioprotective effect of inhibiting the thyroid gland's activity during x-radiation. For this purpose, of 80 5-week old Wistar rats, 64 received cervical irradiation with 15 Gy (single dose). During irradiation, endocrine intervention was done, using thyroxine (T(4)), T(4) plus iodine, or iodine alone compared to placebo. During the endocrine interventions and follow-up, TSH and T(4) concentrations were measured periodically. Histologic examination of thyroid, pituitary gland, or the hypothalamus and any suspect lymph nodes, lungs, and liver was performed after 6 and 54 weeks. It was found that during the endocrine intervention, plasma levels of TSH were lower in rats given T(4) and higher in rats given iodine. After 6 and 54 weeks, no significant reduction in hypothyroidism or thyroid carcinoma was found between the different groups of rats given any endocrine intervention or no intervention. In conclusion, the administration of T(4), iodine or the combination during x-irradiation does not protect against radiation-induced thyroid damage.

The effect of cervical X-irradiation on activity index of thyrocytes and plasma TSH: a pre-clinical model for radiation-induced thyroid damage

Because radiotherapy in the head and neck region is necessary in the treatment of childhood cancer, possibilities to prevent damage to the thyroid gland must be explored. We developed a model in which radiation-induced effects can be investigated in a way that these effects can be quantified, using thyroid dysmorphology and plasma TSH. Thirty-five Wistar rats, 5 weeks old, were X-irradiated on the cervical region, with a single dose varying from 0 to 20 Gy. After 6 weeks, TSH, T4 and T3 were determined, and thyroid glands were processed for histological examination by two independent pathologists. A histological classification scale was developed, using follicular size, colloid density and cell height of thyrocytes to measure hyperplasia and hypertrophy. By the sum of these scores, a cell-activity index was calculated, which was related to plasma TSH concentration. Numbers of PAS-positive droplets and epithelial desquamation were also counted. Inter-observer reliability was assessed. Good to very good reliability was found for scores of follicular size, colloid density and cell height. Significant increase of cell-activity index was found after 10, 15 and 20 Gy. The plasma TSH concentration was positively correlated to the cell-activity index, increasing with radiation-doses up to 15 Gy. The number of desquamated cells was significantly increased after radiation doses >10 Gy, with moderate reliability. In conclusion, this model using cell-activity index of thyrocytes together with plasma thyrotropin concentrations and desquamation of cells can be used for interpretation and future (pre-clinical) studies of prevention of radiation-induced thyroid damage.

Transfer factors of radioiodine from volcanic-ash soil (Andosol) to crops

In order to obtain soil-to-plant transfer factors (TFs) of radioiodine from volcanic-ash soil to agricultural crops, we carried out radiotracer experiments. The mean values of TFs (on a wet weight basis) of radioiodine from Andosol to edible parts of crops were as follows: water dropwort, 0.24; lettuce, 0.00098; onion, 0.0011; radish, 0.0044; turnip, 0.0013 and eggplant, 0.00010. The mean value of the TFs of radioiodine for edible parts of wheat (on a dry weight basis) was 0.00015. We also studied the distributions of iodine in crops. There was a tendency for the TFs of leaves to be higher than those of tubers, fruits and grains. A very high TF was found for water dropwort, because this plant was cultivated under a waterlogged condition, in which iodine desorbed from soil into soil solution with a drop in the Eh value. The data obtained in this study should be helpful to assess the long-lived 129I (half life: 1.57 x 10(7) yr) pathway related to the fuel cycle.