Evaluation of quantitative planar 90Y bremsstrahlung whole-body imaging

Objectives Several studies with high-dose administration of ⁹⁰Y labeled antibodies have paved the way for the possibility to image ⁹⁰Y without admixture of ¹¹¹In. It has been shown earlier that it is possible to perform quantitative ⁹⁰Y bremsstrahlung SPECT for dosimetry purposes with reasonable accuracy. However, whole body (WB) activity quantification with the conjugate view method is not as time consuming as SPECT and has thus been the method of choice in several studies. We have investigated the possibility of using the conjugate view method for quantification of ⁹⁰Y using simulated WB images. The method was evaluated in terms of accuracy of estimated WB and organ activities.

Methods The SIMIND MC code with the NCAT phantom was used to simulate WB ⁹⁰Y bremsstrahlung images. Activity distributions were selected to correspond to patient studies. A GE VH/Hawkeye system was simulated. Scatter, backscatter and septal penetration compensation was performed with inverse filtering. An X-ray simulation program was used to generate WB scout images, which were used for attenuation correction. Organ activities were calculated in ROIs that exactly covered the organs. Corrections for background, overlapping activity and source extension in the depth direction were applied on the ROIs.

Results Total-body activities were overestimated by around 10%, which is a reasonable overestimation since correction for source extension was not applied on the WB images. The accuracy of the organ activities was mostly within 15%. The estimates were dependent on the location of the background ROI.

Conclusions The results suggest that it is possible to quantify ⁹⁰Y activity in ROIs with reasonable accuracy if proper background and overlap compensations are implemented. The method also gave a significant improvement in image quality.