Comparison of tumor to normal tissue count ratio using static and SPECT images

Objectives Radioembolization using Yittrium-90 (Y-90) microspheres treatment for unresectable hepatic tumor requires image analysis using Tc-99m macro aggregated albumin (MAA) administered through a hepatic artery. The purpose of this research is to determine if static image analysis compared to SPECT analysis significantly affects the calculated tumor to normal ratios (TN).

Methods Forty- seven patients with metastatic hepatic tumor were administered approximately 148 MBq of MAA. Following administration, static and SPECT images were obtained. TN were calculated using two different methods. First method used count data from regions of interest (ROI) drawn on SPECT images and was calculated as the counts per voxel for an iso-contour ROI based on the FWHM from the tumor divided by the counts per voxel for adjacent normal tissue. Second method used count data from an iso-contour ROI drawn on static images and was calculated as the average counts from tumor tissue divided by the average counts from adjacent normal tissue. The two methods were compared using Student’s T-test.

Results Average TN from the method using the SPECT data was 5.1 ± 4.9 (range of 0.8 and 22.3). The average TN from static image analysis was 2.5 ± 0.8 (range of 1.2 and 4.3). The difference is a statistically significant (p-value = 0.0005).

Conclusions TN range from SPECT analysis is wider when compared to the TN from static image analysis suggesting that the SPECT method may be more representative of the hetero-distribution of the microspheres within tumorous tissue. With the use of SPECT imaging, a more representative distribution of microspheres can lead to a better understanding of the effective treatment dose using Y-90 microspheres treatment for metastatic hepatic tumors.