DOSIMETRY OF RADIATION SCATTERED TO THYROID-GLAND FROM PROPHYLACTIC CRANIAL IRRADIATION FOR CHILDHOOD LEUKEMIA

Dosimetry of radiation scattered to the thyroid gland was performed in 1 7 children (9 boys, 8 girls) who were treated for acute lymphoblast ic leukemia and received cranial irradiation for prophylaxis against c entral nervous system leukemia at a median age of 4 years and 2 months (range, 1 year and 1 month to 14 years). The absorbed dose to the thy roid gland in these children ranged from 0.7% to 7.3 % of the dose del ivered to the cranium. Thus the total dose to the thyroid gland ranged from 0.13 to 1.32 Gy by the end of the entire course of cranial irrad iation. Doses tended to be larger in younger children, but the radiati on source also had a large influence on the dose to the thyroid gland; that is, the absorbed dose to the thyroid gland with delivery by line ar accelerator was smaller than that by cobalt irradiation. Long-term survivors treated with cranial irradiation for acute leukemia during c hildhood should be followed for the possible development of thyroid di seases, including malignant tumors, for a long period.