Answer to Question #302 Submitted to "Ask the Experts"

Q

I do medical ultrasound and am at odds with our nuclear medicine technologists who feel I am being ridiculous in my avoidance of doing their patients immediately after they have been injected with isotopes. I feel, where avoidable, avoid any obvious unnecessary radiation exposure. Where can I get exposure information for these technologists who tell me there is "no radiation exposure" to me? Of course there is.

A

You are correct in assuming that there is radiation coming from nuclear medicine patients. If this were not the case, then nuclear medicine imaging would not be possible. The question is, "Is there enough radiation coming from a nuclear medicine patient to cause significant exposure potential for an ultrasonographer?" NCRP Report No. 124 Sources and Magnitude of Occupational and Public Exposures from Nuclear Medicine Procedures contains the most up-to-date information on this subject. Particularly useful is Table 5.1 which gives the surface dose rates for 99mTc MDP bone scan patients for 5 minutes, 4 hours and 24 hours after injection. The highest surface dose rate is at 5 minutes after injection and it is approximately 0.09 mGy/hr (9 mrad/hr). As can also be seen from this Table, at 1 meter from the patient the dose rate is 10 times lower. The typical exposure rate at 1 meter from a diagnostic nuclear medicine patient is less than 0.01 mGy per hour (less than 1 mR per hour).



Table 5.2 compares the total integrated doses at skin surface and various distances for the commonly performed nuclear medicine procedures. Table 5.3 indicates that the annual whole body doses received by nuclear medicine personnel is approximately 4000 uGy per year (400 mrem per year) while for other nonnuclear medicine hospital personnel it is approximately 1 mrem per year. It is reasonable to expect nuclear medicine personnel (who not only handle injection and imaging of the patients but also prepare tagged compounds, verify accuracy of doses, provide for radioactive waste disposal, etc.) receive the highest annual doses from nuclear medicine practice. All others receive only a small fraction of the dose received by nuclear medicine personnel.



The best way to answer your question is through personnel monitoring. If you do not already have a film badge, request one and a ring badge as well. Measurements over a three-month period should be sufficient to determine the maximum potential for exposure from these patients. In general, diagnostic nuclear medicine patients are not considered to represent a significant exposure potential. That is why it is acceptable for them to be treated as outpatients and released immediately after their imaging or other diagnostic procedure is complete. There can always be exceptions to every rule.



The best way to determine whether or not these patients represent significant exposure to a unique group, such as ultrasonographers, is through monitoring. Experience indicates that they do not represent significant exposure potential. NCRP Report No. 105 Radiation Protection for Medical and Allied Health Personnel recommends that the Radiation Safety Officer be contacted for a review of the situation in ultrasound. NCRP Reports can be ordered from the NCRP Web Site.



Kenneth L. Miller, CHP

Medical Health Physicist