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Effect of Radioiodine Therapy on Pulmonary Alveolar-Capillary Membrane Integrity

Radiation Medicine Centre and Radiation Safety Systems Division, Radiation Medicine Centre, Bhabha Atomic Research Centre, Parel, Bombay

Correspondence: For correspondence or reprints contact: Dr. A.M. Samuel, Head, Radiation Medicine Centre, Bhabha Atomic Research Centre, c/o TMC Annexe, Parel, Bombay-400 012, India.

ABSTRACT

The effects of large doses of radioiodine on the pulmonary alveolar-capillary membrane using ^99mTc-DTPA clearance as an index of pulmonary damage in subjects with pulmonary metastases of differentiated thyroid carcinoma were studied. Methods: Technetium-99m-DTPA radioaerosols were generated by a dry aerosol generator. Data were acquired and analyzed for clearance half-time from the lungs with a scintillation camera. The study was carried out on 35 thyroid cancer patients with pulmonary metastases and on 32 patients without metastases; the results were compared to those of a control group comprising 52 subjects. The radiation dose delivered to the lungs from the therapeutic dose was calculated using MIRD methodology. Results: Cumulative radioiodine doses varied from 5.9 to 44.2 GBq (158–1194 mCi). The half-time clearance of ^99mTc-DTPA was comparable in both patient groups and was not related to the total administered radioiodine dosage or to the radiation dose delivered to the lungs. No changes were observed for periods up to 5 yr after receiving the last radioiodine dosage. Seven patients followed at regular intervals from 6 mo to 2 yr did not show abnormal ^99mTc-DTPA clearance values. One patient did show low ^99mTc-DTPA clearance half-time values, which were symptomatic radiation pneumonitis. She had received a total dose of 34 GBq (922 mCi) over a 4-yr period. Conclusion: The incidence of pulmonary damage resulting from radioiodine therapy for lung metastases of differentiated thyroid cancer is negligible, as evidenced by the normal pulmonary clearance half-time of ^99mTc-DTPA aerosols.

Key Words: alveolar-capillary membrane integrity • radioiodine therapy • thyroid cancer