Modeling the absorbed dose to the common carotid arteries following radioiodine treatment of benign thyroid disease
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TECHNICAL NOTE
Modeling the absorbed dose to the common carotid arteries following radioiodine treatment of benign thyroid disease Jeppe Lerche la Cour • Per Hedemann-Jensen Jens Søgaard-Hansen • Birte Nygaard • Lars Thorbjørn Jensen
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Received: 13 February 2013 / Accepted: 9 July 2013 Ó The Japanese Society of Nuclear Medicine 2013
Abstract Introduction External fractionated radiotherapy of cancer increases the risk of cardio- and cerebrovascular events, but less attention has been paid to the potential side effects on the arteries following internal radiotherapy with radioactive iodine (RAI), i.e. 131-iodine. About 279 per million citizens in the western countries are treated each year with RAI for benign thyroid disorders (about 140,000 a year in the EU), stressing that it is of clinical importance to be aware of even rare radiation-induced side effects. In order to induce or accelerate atherosclerosis, the dose to the carotid arteries has to exceed 2 Gy which is the known lower limit of ionizing radiation to affect the endothelial cells and thereby to induce atherosclerosis. Objective To estimate the radiation dose to the carotid arteries following RAI therapy of benign thyroid disorders. Methods Assuming that the lobes of the thyroid gland are ellipsoid, that the carotid artery runs through a part of the lobes, that there is a homogeneous distribution of RAI in the lobes, and that the 24 h RAI uptake in the thyroid is
35 % of the 131I orally administrated, we used integrated modules for bioassay analysis and Monte Carlo simulations to calculate the dose in Gy/GBq of administrated RAI. Results The average radiation dose along the arteries is 4–55 Gy/GBq of the 131I orally administrated with a maximum dose of approximately 25–85 Gy/GBq. The maximum absorbed dose rate to the artery is 4.2 Gy/day per GBq 131I orally administrated. Conclusion The calculated radiation dose to the carotid arteries after RAI therapy of benign thyroid disorder clearly exceeds the 2 Gy known to affect the endothelial cells and properly induce atherosclerosis. This simulation indicates a relation between the deposited dose in the arteries following RAI treatment and an increased risk of atherosclerosis and subsequent cerebrovascular events such as stroke. Keywords Radiation
Radioiodine 131I Thyroid Arthrosclerosis
Introduction J. L. la Cour (&) L. T. Jensen Section of Clinical Physiology, Department of Diagnostics, University Hospital of Glostrup, 2600 Glostrup, Denmark e-mail: [email protected] P. Hedemann-Jensen J. Søgaard-Hansen Department of Radiation and Nuclear Safety, Danish Decommissioning, 4000 Roskilde, Denmark B. Nygaard Section of Endocrinology, Department of Medicine, University Hospital of Herlev, 2630 Herlev, Denmark L. T. Jensen Department of Clinical Physiology and Nuclear Medicine, University Hospital of Herlev, 2630 Herlev, Denmark
It is well known that external-fractionated radiotherapy of cancer increases the risk of atherosclerosis, i.e. head and neck cancer patients have an incr
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