PET/CT imaging using half the recommended activity

Objectives According to regulatory norms, in a PET/CT patient waiting room there should be a distance of 1.5meter between any two injected patients. This restricts the number of patients who can be injected at a time and increases the interval between injections. With increased use of time of flight PET scanners, the increased sensitivity can result in reduction in dose or scan time. This requires a relook into workflow and the dose of isotope used. To see impact on effective dose and work flow in a PET/CT facility with reduction of injected dose to half the recommended dose.

Methods We evaluated 52 patients in this study (25 males, 19 females, 8 children less than 12yr old). All the patients except one weighed less than 80kg. All pregnant and diabetic patients with sugar levels >150mg/dl were excluded. 25 patients were injected with half the recommended dose (2.5MBq/kg body weight). The dose rate at 1metre distance was measured immediately post injection and 1hr post injection using a survey meter.

Results The average dose rate at 1metre at the time of injection with regular and half dose was 5.6±0.7mR/h and 3±1.1mR/h respectively; and at 1hour post injection was 2.1±1.05mR/h and 1.2±0.283mR/h respectively. Of the 8 children included, 2were injected with the full dose and showed an average dose rate of 3.65±0.49mR/h at 1mt immediately after injection and 1.15±0.35mR/h 1hr post injection. The rest were injected with half the recommended activity and 1metre dose rate immediately after injection was 2.65mR/h and 0.983mR/h at 1hr post injection. The images acquired were found acceptable by the Nuclear Medicine Physicians.

Conclusions This study suggests that dose reduction reduces the radiation exposure to the patient, personnel and general public without any associated deterioration in scan quality. This may have tremendous impact on the planning of work flow.