Radiation dose to the upper spine from therapeutic administrations of iodine-131-sodium iodide.

Abstract

Thyroid cancer patients sometimes receive conventional external irradiation to the neck in addition to radioactive iodine therapy. In these situations, knowledge of the radiation dose already received by the spine in the neck area from the radioiodine administration can be an aid in treatment planning. This paper gives an estimate of the radiation dose to the upper spine from administration of 3700 MBq of 131I-sodium iodide. Monte Carlo codes used to estimate radiation dose from internal emitters usually give absorbed doses to the whole spine or marrow. One such code was modified to give a dose only to the upper spine region near the thyroid. Calculations assumed a thyroid uptake of 10% of administered activity and retention with a 35-hr effective half-time. Activity in the remainder of the body was assumed to clear with a 6-hr half-time to urine. Under these assumptions, the dose to this upper spine region was about 200 mGy.