Optimization of Scintillator Thickness for Betabox 2.0, a System for Quantitative Measurement of Radiopharmaceuticals In Single Cells.
Abstract
Purpose
The BetaBox 2.0 is a high sensitivity, low noise instrument that measures positron and electron emissions from radiopharmaceuticals in single cell samples. The goal of these measurements is to elucidate the biological differences among individual cells by measuring radiopharmaceutical accumulation, which can be used to identify subpopulations of cells resistant to treatment, and aid in the development of radiopharmaceuticals.
Methods
The newest generation BetaBox 2.0 is composed of an array of microfluidic cell traps atop a plastic scintillator layer which is read out by an array of SiPMs. This differs from the design of the original BetaBox, which used a Position Sensitive Avalanche Photo-diode (PSAPD). This change was made to improve the scalability of the system and increase the number of cells that can be simultaneously interrogated from tens to a few thousand. The scintillator included in this new design introduces background noise from gammas which can travel to neighboring cells. This design change required GATE simulations to determine optimal design parameters, such as the plastic scintillator thickness.
Results
GATE simulations were performed on an 8x8 array of SiPMs with varying thickness of plastic scintillator above them. Based on the ratio of the signal from charged particles versus the background noise from gammas, and the amount of energy deposited from an F-18 and Ga-68 source, an optimal scintillator thickness of 200-300 micrometers was determined.
Conclusion
This work indicates that the low noise, high sensitivity capabilities needed to detect the radioactive signal emitted from single cells via plastic scintillator above SiPMs are feasible. This signal can be used to investigate biological differences between a large number of cells, yielding high statistical power. This information should result in a better understanding of bulk tumor quantities, such as FDG accumulation in vivo, to provide outlooks on treatment efficacy and new treatment options.