THE RADIATION EXPOSURE OF THE PATIENT FROM STABLE-XENON COMPUTED-TOMOGRAPHY

For stable-xenon computed tomography (CT), an X-ray examination for me asurement of cerebral blood circulation in the brain, the radiation ex posure of the patient was determined in order to estimate the risk of inducing cancer. Organ doses of brain, eyelenses, thyroid and gonads h ave been calculated using the measured air kerma free-in-air on the ax is of rotation and organ-specific conversion factors calculated with t he Monte Carlo method. Dose measurements with TLD-100 rods using a hum anoid Alderson phantom were carried out for verification of the calcul ated 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 diff erent regions of the brain and consequently an inhomogeneous dose dist ribution. From an estimation of the radiation-induced risk using the e ffective dose of 1.6 mSv it follows that one additional fatal cancer p er 12500 stable-xenon CT examinations has to be expected. The organ do ses of eyelenses and thyroid located in the region of scattered radiat ion 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.