Various hospital staff members are exposed to radiation during the sentinel node procedure. Because the surgeon is in closest contact with both tumor and sentinel node, dose calculations will be focused primarily on this person. Radiation exposure of others (e.g., nurses and pathology personnel) can be deduced from the values that apply to the surgeon. The skin of the surgeon's hands is expected to receive the highest dose and therefore serves as the dose-limiting organ. The radiation exposure of the surgeon during the operation is determined by the amount of tracer that is retained around the tumor, the distance from the injection depot to the surgeon's hands, and the duration of exposure. The amount of tracer uptake in the sentinel node is small and will not exceed a few percent of the total injected dose [18,19].
The amount of remaining activity at the moment of surgery is determined by the injected tracer dose and the time delay since injection. The physical decay of 99mTc can be calculated as
At = A0e~x t where At is the remaining activity at surgery, A0 is the amount of radioactivity at the moment of injection, X is the decay constant of 99mTc (0.11 h_1), and t is the time interval between injection and surgery. Every 6.02 h the radioactivity will be halved. To a lesser extent, the remaining activity is related to the amount of transported and excreted tracer, which is relatively small. Finally, a deeper injection results in more shielding by the overlying soft tissues and, consequently, in a lower exposure rate outside the body.
We performed dose-rate measurements in phantoms and in patients to calculate the radiation dose for exposed personnel.
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