TREATMENT OF MICRONODULAR LUNG METASTASES OF PAPILLARY THYROID-CANCER- ARE THE TUMORS TOO SMALL FOR EFFECTIVE IRRADIATION FROM RADIOIODINE

Our purpose was to determine if micronodular lung metastases from papi llary thyroid cancer had diameters that were less than 1 mm and theref ore of a size for which irradiation by radioiodine (I-131) is ineffici ent. In five patients, lung metastases seen on computed tomography (CT ) were enumerated and sized in the entire right lung and right upper l ung giving volumes of measurable, ie, more than 1 mm diameter, tumors. Concentrations of diagnostic I-131 were quantified scintigraphically in the same regions. Fractions of administered I-131 per milliliter of tumor and the absorbed radiation from the subsequent treatments were calculated to see if the I-131 levels in lungs were greater than expec ted for the visible tumor volumes. Two other patients manifesting simi lar findings had lung biopsies that were reviewed for size of metastas es. The calculated fractions of administered activity per milliliter o f tumor and the absorbed radiations from the treatments with I-131 wer e exceptionally high. Biopsies revealed numerous tumors below the reso lution of CT. We conclude that the fractions of administered activity and absorbed radiations of I-131 i, tumors were high because the measu red tumor volumes underestimated the total tumor volumes. Many lung me tastases were less than 1 mm in diameter.