Radiation exposure from FDG PET patients with multiple same day appointments

Objectives Investigate radiation exposure to staff and public from patients leaving the PET facility for other clinic areas.

Methods 20 patients with same day appointments after PET were surveyed to determine time spent in various areas as well as for the number and age of accompanying people. 28.7% of patients at our institution have same day appointments with their physiicans and 34% have multiple appointments. Exposure rates were calculated at various distances and time from injection using the accepted dose rate constant to determine potential exposure to others. Survey meter measurements on some patients was used to determine exposure variation as a function of distance.

Results 555 MBq FDG at 0.5m for 1 hr begining 95 min postinjection resulted in 0.08 mGy calculated air kerma. Measured results were less,see Table. Patients were frequently in close contact with others for prolonged periods. Waiting rooms with chairs <1m apart resulted in the greatest exposure (average waiting room time 70.4 min). One patient brought three children with them while others drove long distances. Exposure was low for physicians spending 15 min at 1 m with a patient. However, several of our physicians routinely see 5-9 same day patients per week so the cumulative amount (~12 mrem/month) may make behavioral changes desirable.

Conclusions Interpreting exposure measurements at ≤1m is challenging since patients do not behave as point sources. At 0.5 m measurements were ~70-80% of expected. While total exposure is well below regulations, simple modifications result in a desirable decrease in exposure. Clinicians could delay appointments and patients could maintain distance from others. Children should not be brought to appointments

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Measured Patient vs. Expected Exposure Rate 1 hr After 555 MBq Injection

Typical survey meter results reported in mR/hr taken laterally at mid-chest region.