Optimization of the image contrast in SPECT-CT bremsstrahlung imaging for Selective Internal Radiation Therapy of liver malignancies with Y-90 microspheres

TL;DR

This study optimizes SPECT-CT imaging contrast for Y-90 bremsstrahlung imaging in liver cancer therapy by identifying the best energy window, demonstrating higher contrast with high-energy collimators at 110-135 keV.

Contribution

The paper introduces an optimized energy window selection for Y-90 SPECT imaging, improving contrast and contrast recovery through Monte Carlo simulations and experimental validation.

Findings

High-energy collimators yield better contrast than medium-energy ones.

Maximum contrast and CRC occur at 110-135 keV energy window.

Optimization improves clinical SPECT imaging quality for Y-90 therapy.

Abstract

The quality of SPECT Bremsstrahlung images of patients treated with Y-90 is poor, mainly because of scattered radiation and collimator septa penetration. To minimize the latter effect, High Energy (HE) or Medium Energy (ME) collimators can be used. Scatter correction is not possible through the methods commonly used for the diagnostic radionuclides (Tc-99m, etc.) because the Bremsstrahlung radiation does not have distinct photopeaks, but a broad spectrum of energies ranging from zero to the maximum one detectable by the gamma-camera crystal is registered. Scatter radiation and collimator septa penetration affect the Contrast and the Contrast Recovery Coefficient (CRC) : our research focused on finding the best energy position for the acquisition window in order to maximize these parameters. To be guided in this finding, we first made a Monte Carlo (MC) simulation of a SPECT acquisition of a Y-90 cylindrical phantom and then we measured at different energies the Line Spread Function (LSF) of a linear Y-90 source inserted in a scatter medium. Finally we acquired the NEMA IEC Body phantom filled with Y-90 chloride at different energies and using different setups in order to measure the Contrast and the CRC in different conditions with the purpose of optimizing the clinical SPECT acquisition procedures. The final results showed that Contrast and CRC are higher for HE collimators compared to ME collimators and they have a maximum for the larger spheres at 110 - 135 keV.