EFFECT OF RADIOIODINE THERAPY ON PULMONARY ALVEOLAR-CAPILLARY MEMBRANE INTEGRITY

The effects of large doses of radioiodine on the pulmonary alveolar-ca pillary membrane using Tc-99m-DTPA clearance as an index of pulmonary damage in subjects with pulmonary metastases of differentiated thyroid carcinoma were studied. Methods: Technetium-99m-DTPA radioaerosols we re generated by a dry aerosol generator. Data were acquired and analyz ed for clearance half-time from the lungs with a scintillation camera. The study was carried out on 35 thyroid cancer patients with pulmonar y metastases and on 32 patients without metastases; the results were c ompared to those of a control group comprising 52 subjects. The radiat ion dose delivered to the lungs from the therapeutic dose was calculat ed using MIRD methodology. Results: Cumulative radioiodine doses varie d from 5.9 to 44.2 GBq (158-1194 mCi). The half-time clearance of Tc-9 9m-DTPA was comparable in both patient groups and was not related to t he total administered radioiodine dosage or to the radiation dose deli vered to the lungs. No changes were observed for periods up to 5 yr af ter receiving the last radioiodine dosage. Seven patients followed at regular intervals from 6 mo to 2 yr did not show abnormal Tc-99m-DTPA clearance values. One patient did show low (TC)-T-99m-DTPA clearance h alf-time values, which were symptomatic radiation pneumonitis. She had received a total dose of 34 GBq (922 mCi) over a 4-yr period. Conclus ion: The incidence of pulmonary damage resulting from radioiodine ther apy for lung metastases of differentiated thyroid cancer is negligible , as evidenced by the normal pulmonary clearance half-time of Tc-99m-D TPA aerosols.