JPNM Physics

511 keV Collimated Imaging

Radiation Safety Issues

The imaging room environment has been surveyed during a hot activity phantom measurement involving about 70 mCi of F-18. The following table highlights the exposures of interest with the activity normalized to a 5 mCi F-18 FDG injection:

Location	Exposure Rate microR/hr per 5 mCi F-18
1 meter	640
4 meters	68
1 floor down	11

SUMMARY

Occupational Workers

The occupational workers are permitted 5000 mR per year by NRC regulations. Of course, much lower values are strictly enforced by institutional ALARA policies. If the technologist must attend to a computer within 1 meter of patients with 5 mCi of F-18 injected (a worst-case scenario that "hot" patients are continually replacing patients in whom F-18 activity has decayed), then a daily exposure would be 5.12 mR. A weekly exposure would be 25.6 mR, and the annual exposure would be 1280 mR. This is well below the occupational limit, but nearing the level of ALARA concern. However, pregnant radiation workers must keep exposures to a level 0.1 times that of the 5000 mR level, or 500 mR. Since this calculation was made under the assumption of proximity to hot patients throughout the entire workday, the pregnant worker should not be expected to exceed even the strict level of 500 mR if she obeys ALARA principles (maximizes distance and minimizes time in proximity) whenever possible.

Operating at 4 meters instead of 1 meter would bring the annual exposure from F-18 to 136 mR.

Non-occupational Workers

The workers in the floor below the imaging room are exposed to 11 microR/hr, which converts to 88 microR/day, 440 microR/week, and 22 mR per year. Note that this value is assuming the bed is occupied by a patient with 5 mCi of F-18 for 8 hours a day. Nuclear medicine facilities are regulated to keep exposures to the public less than 250 mR per year in the nearby corridors and surrounding workspaces. The worst-case level of 22 mR per year is well below this value.