Gamma camera/SPECT QC: Can ⁵⁷Co be used to perform center of rotation?

Objectives Performing center of rotation (COR) on a gamma camera/SPECT system is most often accomplished using ^99mTc. Using another radionuclide, rather than ^99mTc, would: 1. Save the Nuclear Medicine department the rising cost of a daily dose of ^99mTc and 2. Offer another technique for doing COR should ^99mTc not be available to one’s facility. The purpose of this study is to see if COR can be performed using ⁵⁷Co.

Methods Five cameras were used for this study; Siemens Symbia and GE Healthcare’s Infinia Hawkeye 4, Millenium MG, Millenium VG 3/8”, and Optima 640 NM/CT. The ^99mTc point sources used had a mean activity of 1.05±.09mCi. The ⁵⁷Co pen point marker used had an activity of 250 µCi (calibrated on 04/01/12). Each camera’s COR protocol was followed and 5 trials per source were performed on each camera. When using ⁵⁷Co, the isotope/energy settings were changed accordingly. The data obtained from each trial were processed using the "COR test" option in a Xeleris 3.1 Workstation and graphs were generated displaying COR X values. COR X values <.5mm are acceptable for COR performances per our physicians and physicists.

Results The ⁵⁷Co trials produced the following mean COR X values; .19±.02mm (Infinia Hawkeye 4), .14±.04mm (Optima 640 NM/CT), .27±.16mm (Millenium VG 3/8”). The Symbia’s COR protocol required five 1-2mCi point source containers of ^99mTc and therefore ⁵⁷Co could not be used. When attempting to use ⁵⁷Co for the Millenium MG’s COR protocol, the camera predicted it would take ≈3 hours to obtain enough counts/position and therefore no trials were completed. The ^99mTc trials produced the following mean COR X values; .16±.01mm (Infinia Hawkeye 4), .11±.02mm (Optima 640 NM/CT), .11±.01mm (Millenium VG 3/8”).

Conclusions Performing COR with ⁵⁷Co on the Infinia Hawkeye 4, Optima 640 NM/CT, and the Millenium VG 3/8” resulted in COR X values <.5mm. These values are acceptable and similar to those of ^99mTc but more trials need to be completed to form a solid conclusion. ⁵⁷Co cannot be used to perform COR on the Millenium MG and Symbia when following their specific COR protocols.