131I effective half-life and dosimetry in thyroid cancer patients.

UNLABELLED: (131)I treatment in thyroid cancer patients may induce side effects, including extrathyroidal cancer and leukemia. There are still some uncertainties concerning parameters that may influence the effective half-life of (131)I and the absorbed doses by extrathyroidal organs. METHODS: Whole-body retention of radioiodine was measured in 254 patients, and repeated quantitative whole-body scans and measurements of the urinary excretion of (131)I were performed on 30 of these patients. RESULTS: The mean effective half-life (10.5 h) was shorter by 31%, with little difference between patients, in the 36 patients who received recombinant human thyroid-stimulating hormone than in the 218 patients who underwent thyroid hormone withdrawal (15.7 h). The residence times in the stomach and in the rest of the body were significantly shorter in patients who received recombinant human thyroid-stimulating hormone than in patients who underwent withdrawal, but the residence times were similar in the colon and bladder. CONCLUSION: In patients who undergo thyroid hormone withdrawal, the longer mean effective half-life is mainly due to delayed renal excretion of (131)I and results in dose estimates higher than the data in report 53 of the International Commission on Radiological Protection, which were obtained from healthy, euthyroid subjects.

Imaging of the distribution of (90)y-ibritumomab tiuxetan in bone marrow and comparison with pathology.

PURPOSE: Radioimmunotherapy with anti-CD20 antibodies (Abs) labeled with beta-emitters is now used in the treatment of non-Hodgkin's lymphoma (NHL). Because (90)Y is a pure beta-emitter, no direct image of its distribution can be obtained in humans. In this paper, we present in this study imaging data of (90)Y-Ab distribution in human-mantle-cell lymphoma within a mouse model. Describing the actual distribution of the radionuclide at the level of particles range may have important impact on patient dosimetry and therapy treatment planning. EXPERIMENTAL DESIGN: NOD/SCID mice were grafted with a human NHL cell line that involves the bone marrow. The mice were treated with (90)Y-ibritumomab tiuxetan (Zevalin); Schering AG, Germany) and sacrificed 2 hours after Zevalin administration. Tissue sections were then prepared and viewed under conventional microscopy. The distribution of the radioactivity in mouse femur was determined by using digital autoradiography and subsequently correlated with immunohistochemical results. RESULTS: Various extent of bone marrow infiltration was investigated and found to be reproducible. Zevalin uptake was heterogeneous within the bone marrow. However, unspecific mouse monoclonal uptake by accessory myeloid cells gave nonspecific background radioactivity. Treating mice with an irrelevant mouse IgG1 monoclonal antibody (mAb) before Zevalin injection controlled this unspecific uptake, and images were strongly correlated with bone marrow infiltration on histologic analysis. CONCLUSIONS: Our model was reproducible, and allows for the study of various bone marrow involvement with good sensitivity. We demonstrated that imaging of the beta-emitter was possible with good image quality and that (90)Y-Zevalin is distributed heterogeneously within bone marrow. These data suggest that detailed pharmacokinetics may be developed with this model.

Thyroid cancer patients treated with 131I: radiation dose to relatives after discharge from the hospital.

BACKGROUND: Thyroid cancer patients treated with radioiodine are potential source of radiation exposure for other individuals. Thus, we evaluated the radiation dose received by family members of thyroid cancer patients treated with (131)I after hospital discharge. MATERIALS AND METHODS: Seventy-six family members of 56 thyroid cancer patients were included in the study. Thyroid cancer patients were given 3.7 GBq of (131)I and remained in a radiation protection ward for 3 days. Radiation protection recommendations were given to patients and relatives. Life conditions were recorded and radiation doses were monitored using a personal dosimeter. RESULTS AND DISCUSSION: At discharge, the mean residual activity was 188 MBq. The mean radiation dose delivered to relatives during the 7 days after discharge was low (51.5 µSv) and was similar with either recombinant human thyrotropin (rhTSH) (59 µSv) or withdrawal (50 µSv) (p = 0.37). CONCLUSION: With our current practice, radiation doses to relatives are low and well below international recommendations.