Evaluation of a modified quadruple energy window scatter subtraction algorithm for quantitative imaging with In-111

Abstract

Accurate quantitative imaging for radionuclide uptake in tumors and organs is an important challenge in radioimmunotherapy. Inaccurate determination of uptake could adversely impact the subsequent therapy dose. An overestimation of activity could result in delivering insufficient dose to the tumor site. Conversely, underestimation of tumor uptake could result in reaching toxicity limits of non-target organs. In a growing number of studies, In-111 is used in tracer studies for Y-90 labeled antibody therapy. The objective of this study was to design and study the impact of a modified quadruple energy window scatter subtraction (QEWSS) algorithm on the accuracy of determining In-111 activity in sources of varying area and depth. Quadruple energy window Anger camera images of In-111 in various source volumes were acquired and processed with empirically determined scatter multipliers. The results were compared to the accuracy of determining In-111 based on the standard geometric mean approach which calculates the geometric mean from conjugate views and applies attenuation correction using factors derived from Co-57. The QEWSS algorithm was found to provide the best estimates for In-111 activity in these phantom studies and furnished images with improved contrast that may aid physicians in image interpretation. The QEWSS algorithm described in this study can provide improved radiation absorbed dose estimates for tumors and organs in radioimmunotherapy patients and can be easily extended for other commonly used multiple energy photon emitting radionuclides such as Ga-67 and Tl-201.