Estimating the radiation dose of non-radiation workers from nuclear medicine patients

Introduction:
As a valuable imaging modality, Nuclear Medicine (NM) indications is raising in clinical practice. The remained portion administrated radioactive material in patients’ tissues is a critical issue, especially when the procedure is performed in hospitalized patients, where the non-radiation workers present. The aim of this study was evaluation the dose of non-radiation workers staff from hospitalized NM patients.
Materials and Methods:
Ninety-one patient were selected. Four procedures of Cardiac (TC-MIBI), Bone (TC-MDP), Renal (TC- DTPA) and Lung (TC-MAA) were chosen. The one-day protocol is a clinical routine in this NM department for hospitalized patient referred for cardiac scan. By means of calibrated ionization chamber the dose rate in term of Micro-Sivert per hour (µSv/h) was measured on three positions against patient’s body. On the chest wall, 30 cm distance and 1.5 meter away from the patient. These measurements were done on five phases of immediately after injection, 30 minutes, 1 hour, 3 hours and 4 hours after injection of the radiopharmaceutical. All of measurements were in place without radiation from the other patients and medical sources where the only source was the indicated patient.
The total absorbed dose of patients were estimated by equation Dose= Dose rate × time. The integral of exposure time at different distances and positions were estimated for average situation in other departments.
Results:
Each of hospital wards referred averagely 3 patients to NM department per month. The average measured dose rate at the chest wall were 92,120, 84, 22 and 6 µSv/h at time of injection, 0.5, 1, 3 and 4 hours after injection respectively. The dose rate before leaving the NM department at chest wall, 30 cm from patient and 1.5 meters anterior away from patient were 5.5, 4 and 3 µSv/h respectively. On monitoring and questionnaires, each personnel exposed to patient’s radiation at 1.5 meter for 1.5 hours and 35 minutes at 30 cm away from the patient. The estimated dose of staff were 6.8±3.6 (2.1 to 8.2)
µSv/h. The most exposure was for ICU and CCU ward where the design of department and sensitivity of patient care leads to more exposure time. CCU ward has referred the most patients (average 10 patients per month) to NM department. The most radiation dose was for bone scan and then cardiac scan. The average received dose is 244 µSv per year for staff.
Conclusion:
Although this study is a rough estimate about the staff dose but, the exposure of hospital wards from Nuclear medicine patients is negligible according to radiation protection limits for public, but It is recommended to design appropriate policy about patient release and clearance of radioactive materials. It is critical to have completing study by personal dosimeters such as film badge or TLD to accurately measure absorbed dose.