The Study On External Radiation Protection From Patients Received ¹⁸F

As one of the most important applications in nuclear medical imaging devices,Positron Emission Tomography (PET) has been used successfully and widely forclinical diagnosis in recent years. Patients in PET imaging need injectingpositron-emitting isotopes(18F) into the body. Thus patients received 18F are externalradiation sources and have exposure potential to the members of the public whocontact with these patients. The aims of the study were to measure absorbed doserate in air of the patient after 18F injection, to investigate the difference between themeasurement results of absorbed dose rate in air and results calculated by twomethods, to estimate the effective dose received by family members, fellowtravelers and colleagues without restriction, to evaluate the radiation safety of thepublic members who contact with these released patients, and to offer reference datafor radiation protection.The study population consisted of 20 patients. The measurements were takenright after patients were injected 18F and until patients were released. Absorbed doserates in air of each patient were measured at 0m, 0.3m,0.5m,1.0m ,1.5m from theanterior mid trunk of patients using 450P(VICTOREEN). The doses received bystaff member were measured by TLD. Based on the measurement results ofabsorbed dose rates in air of 20 PET imaging patients before leaving hospital, publicdoses received by family members, fellow travelers and colleagues who mightcontact with a patient were estimated using Mountford's method. Then the safetyof the contact between a patient and a public member could be evaluated accordingto the 131I releasable activity limit that has been released in national safety standardGB18871． The means and SDs(standard deviation) of absorbed dose rates in air at 0.3m,lm and 1.5m distances from a patient were shown in table . The measurement ofabsorbed dose rate in air is lower than those of calculated by two methods. The resultcalculated by dot source is higher than that of line source. Therefore the dose rate atsmall distance from the patient received injection of 18F can not be calculated simplyby dot source and line source. The doses received by staff members do not exceedthe annual limit for professional persons that has been published in GB18871. Thedoses equivalent received by family members, fellow travelers and colleagueswho contact with a treated patient varied from 0.039 to 0.29mSv if there were norestriction. The public dose received from one PET imaging released patient is lessthan 1 mSv, which is the annual limit in GB18871. The activity of 18F in a releasedpatient who was injected 10mCi conforms to the requirement in national standard. Inorder to reduce additional exposure to the members of public due to contacting withthese patients, more attention should be paid to radiation protection of patientsinjected 18F.The main problem was that public doses estimated using Mountford's methoddid not exactly reflect the real contacting situation.