Hospital staff potentially are exposed to radiation from patients who undergo myocardial perfusion imaging (MPI). In a letter published online May 15 in the Journal of the American College of Cardiology, the authors estimated occupational radiation exposure with MPI and offered ways to reduce it.
Connie W. Tsao, MD, of the Cardiac MR Center at Beth Israel Deaconess Medical Center in Boston, and colleagues pointed out that patients administered radioactive pharmaceuticals for MPI studies continue to emit radiation after the study has been completed. Caregivers in close proximity to them may be exposed to radiation for the first several hours after injected dose.
To measure that effect, they made radiation measurements in 56 patients referred for single day Tc-99m sestamibi MPI. The mean Tc-99m administered activity at rest and stress were 381 MBq and 1,135 MBq, respectively.
In 46 patients, they used an ionization chamber and Geiger-Muller survey meter to obtain measurements immediately after study completion at the center of the chest wall, the right elbow, and at 0.3 meter, 1 meter and 2 meters from the right chest wall. They also obtained Geiger-Muller measurements when patients arrived at the hospital floor, and then one, two and four hours after arrival.
They used film badge dosimetry in the other 10 patients. Patient badges were positioned at the spot of sonographer contact during scanning.
For exposure of 27.6 minutes starting after the 90-minute administration of the radionuclide, the anterior chest wall dose equivalent was 0.37 mSv and right chest wall dose equivalent was 0.58 mSv.
Based on a review of 64 echocardiographic studies and transportation logs, they estimated patient contact time for cardiac sonographers to be 14 minutes and for transport staff to be 10 minutes. A right-handed sonographer at the right elbow to the chest wall had a potential radiation dose equivalent to 0.1 to 0.16 mSv at 90 minutes after administration. A left-handed sonographer had a dose equivalent of 0.04 mSv at 0.3 meters. A transport worker had a dose equivalent of 0.02 mSv at 0.3 meters.
Radiation exposure estimates were higher using film badge dosimetry.
Scheduling multiple same-day tests and assigning transport workers to an area for long periods may increase occupational radiation exposure, they wrote. “Non-nuclear medicine personnel do not receive radiation safety training and may be unaware of the potential risks from radiation exposure and the simple methods to protect themselves from radiation emitted by patients. Without guidelines in the management and scheduling of post-MPI patients, a sonographer with repeated exposures may approach or exceed the 20 mSv/year (100mSv/5year) recommended guidelines.”
They recommended rotating staff and arranging schedules to reduce exposure and providing workers with lead aprons during the first four hours after MPI. They also cautioned that vulnerable people in the public, such as pregnant women and children, should avoid close and repeated contact with patients after MPI.
“Our data confirm that radiation exposure to hospital personnel and the public can be minimized by maintaining adequate distance from the patient. Instituting appropriate changes in scheduling, the use of lead shielding, and patient education can further aid in reduction of radiation exposure to others,” Tsao et al concluded.