Objective: To evaluate the effective dose delivered to patients undergoing sentinel lymph node (SLN) lymphoscintigraphy by taking into account both the transmission dose using the CT component of a SPECT/CT system and the (99m)Tc internal emission dose.
Materials and methods: An adult female humanoid phantom and a set of thermoluminescent dosimeters were used in dose measurement from the CT transmission irradiation. The choice of measurement organs in the humanoid was guided by the recommendations described in the International Commission on Radiological Protection report number 103 (ICRP-103). The effective doses due to (99m)Tc internal emission source were re-calculated from measurement data reported in our previous study on the same subject with the use of tissue weighting factors of ICRP-103.
Results: CT transmission dose is the main contribution to the patient total effective dose for both 1-day and 2-day lymphoscintigraphy protocols and for different surgical procedures. Patients undergoing SLN lymphoscintigraphy receive about the same amount of total effective dose of about 3mSv for both 1-day and 2-day protocol, regardless of whether the tissues containing radioactivity would be excised at surgery or not.
Conclusion: Although the total effective dose from using SPECT/CT is equivalent to the annual natural background radiation of about 3mSv, nuclear medicine physicians should be aware of the increase in effective dose for SLN lymphoscintigraphy using hybrid imaging technique of SPECT/CT when compared to conventional planar (57)Co flood source for transmission scan. Results from the current study provide update information in radiation exposure to patients undergoing SLN lymphoscintigraphy with the use of SPECT/CT.
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