The radiation exposure of the patient from stablexenon computed tomography

Abstract

For stable-xenon computed tomography (CT), an X-ray examination for measurement of cerebral blood circulation in the brain, the radiation exposure of the patient was determined in order to estimate the risk of inducing cancer. Organ doses of brain, eyelenses, thyroid and gonads have been calculated using the measured air kerma free-in-air on the axis of rotation and organ-specific conversion factors calculated with the Monte Carlo method. Dose measurements with TLD-100 rods using a humanoid Alderson phantom were carried out for verification of the calculated organ doses. In the case of brain partially located in the region of primary radiation a mean organ dose of 39 mSv was calculated. The dose measurements showed dose equivalents between 6 and 68 mSv in different regions of the brain and consequently an inhomogeneous dose distribution. From an estimation of the radiation-induced risk using the effective dose of 1.6 mSv it follows that one additional fatal cancer per 12,500 stable-xenon CT examinations has to be expected. The organ doses of eyelenses and thyroid located in the region of scattered radiation are so low that biological effects are hardly to be expected. The calculated dose equivalents of 6.5 mSv and 0.5 mSv, respectively, are in good agreement with measurements. The organ dose of gonads amounted to less than 0.07 mSv.

Would thyroid and breast shielding be beneficial in CT of the head?

“…Earlier publications indicate that radiosensitive organs in the neck and thorax make only a small percentage contribution (less than 10 %) to the total effective dose from a CT head scan [2,5]. If effective dose is used uncritically as the measure of risk, it may appear that any efforts to reduce dose in the neck and thorax region will have little impact on overall risk.…”

Xenon-Enhanced Cerebral Blood Flow at 28% Xenon Provides Uniquely Safe Access to Quantitative, Clinically Useful Cerebral Blood Flow Information: A Multicenter Study

“…This is similar to published estimates of 39 mSv. 27 Calculation of CBF depends on a modification of the KetySchmidt technique for blood flow measurement. Rather than using the washout of a tracer, the equation is modified to measure the washin, a more reliable CBF estimate.…”

“…With this technique, no calcula-ble biologic effect on the lens or thyroid could be estimated. 27 A whole-body equivalent dose has been estimated at 40 mSv with 1 Xe-CT study. There is likely some small risk of oncogenesis with CT, though the exact dose and risk are controversial.…”

“…One study estimated that the theoretic rate of fatal cancer formation was 1 per 12,500 Xe-CT studies. 27 For this reason, it seems reasonable to focus the use of Xe-CT CBF studies in patients with serious disorders, in whom the benefit from having access to quantitative data and the ability to examine the response to physiologic challenges outweigh any theoretic radiation risk.…”

A Practical Approach to Interpretation of CBF Measured by Mean of Xenon-CT in Patients with Traumatic Brain Injury~!2010-03-08~!2010-03-29~!2010-09-14~!

“…A study from Seifert [24] calculated that exposure may be associated with one case of fatal cancer out of 12,500 studies. This risk is relatively uncertain.…”