The influence of flood source placement on radiation exposure during quality control testing

This study examined the photon energy distribution and exposure rate from a 250-MBq 57Co flood source during quality control (QC) procedures as a function of source placement and measurement location. The optimum placement of the source to reduce the radiation dose to the nuclear medicine technologist during QC checks was determined.

Measurements of exposure rate were made inside and outside a camera room with the source positioned either above or below the camera head. The energy distribution of the photon field was examined at the same locations using a high-resolution gamma-ray spectrometer. Additional measures of exposure rate were made with the source at various distances from the camera face.

The lowest exposure rates occurred when the source was lying directly on the face of the camera head. The exposure rates at locations inside the camera room increased by a factor of 4.3 +/- 3.0 when the source was placed on an imaging table below the camera head. This increase can be attributed to decreased shielding provided by the camera head.

A large portion of the radiation dose received by technologists during QC checks is due to scattered radiation and x-rays produced by gamma-ray interactions within the camera. This dose can be reduced significantly if QC checks are performed with the flood source lying directly on the inverted gamma camera head rather than placing the flood source on an imaging table under the gamma camera.