Developing a protocol for ⁹⁰Y bremsstrahlung imaging after Transarterial Radioembolization

Abstract

Yttrium-90 (90Y) is an almost pure beta emitter used in Transarterial Radioembolization (TARE). Post-TARE 90Y bremsstrahlung imaging is employed for quantification of the delivered dose. 90Y bremsstrahlung imaging is the most challenging issue in nuclear medicine because of the low photon yield, the continuous and non-pronounced peak of the bremsstrahlung spectrum. GATE Monte Carlo code was employed to find the most proper imaging protocol for 90Y bremsstrahlung imaging. Images were acquired using Medium-Energy Medium-Resolution (MEMR) and High-Energy Medium-Resolution (HEMR) in nine energy windows widths (50 to 500 keV). The quality of images was evaluated using contrast, resolution, sensitivity, Signal-to-Background Ratio (SBR), percentage of total counts in useful field of view, and Contrast-to-Noise Ratio (CNR). The HEMR collimator performed better than the MEMR collimator on all imaging criteria except for the sensitivity. The CNR values were equal in both collimators. Based on the measured parameters, images acquired by the HEMR collimator with the energy window of 50–200 keV are the best protocol for 90Y bremsstrahlung imaging. The findings in this study suggest the imaging protocol for 90Y bremsstrahlung imaging that can be practically used in the clinic.

Energy window optimization in bremsstrahlung imaging after Yttrium-90 microsphere therapy

“…These ranges are consistent with other investigations related energy window optimization with medium energy collimator [6,8,12,13]. Namely, due to the Y-90 Bremsstrahlung energy spectrum has large numbers of low-energy photons, it is concluded that 50-100 keV energy window is the most proper energy window when using the medium energy collimator [23]. Spectral components of 225-300 keV and 300-400 keV in 90Y bremsstrahlung spectrum correspond the region of backscatter, collimator scatter and septal penetration [13].…”

“…It should also be said that a medium energy collimator was used for Y-90 bremsstrahlung imaging in this study and results may vary if a high energy collimator is used. Since the low count of bremsstrahlung photons is the main problem in Y-90 imaging, in case of using high energy collimator, wider ranges of energy width can be resulted in images with an appropriate combination of sensitivity and quality [8,23].…”

“…The safe delivery of high radiation doses to the tumor is made possible by selective intra-arterial injection of microspheres [3]. Imaging post-TARE is recommended in order to confirm the activity distributions of 90 Y microspheres in the patient body and to measure doses delivered to tumors and healthy organs [4,5].…”

“…Many experimental and simulation imaging studies have been conducted on the energy window selection in planar/SPECT bremsstrahlung imaging and detailed information was given in our previous study [11]. In a Y-90 bremsstrahlung imaging optimization study using a Monte Carlo code, the appropriate imaging condition was obtained with a High-Energy Medium-Resolution (HEMR) collimator in the energy range of 50-200 keV [4]. Huey et al (2020) evaluated the image quality parameters in a wide energy range of 60-300 keV using medium energy general purpose (MEGP), high energy general purpose (HEGP), and low energy high resolution (LEHR) collimators in the experimental phantom study, and it was determined that the optimum imaging condition was between 60-100 and 102-138 keV energy ranges with MEGP collimator.…”