TH-AB-BRA-03: Development of a Scintillation Dosimetry System Capable of Real-Time Dosimetry During LDR Brachytherapy Seed Implant

Authors


Abstract

Purpose:

To develop a scintillation dosimetry system with sufficient sensitivity for accurate dose measurements during low dose-rate (LDR) brachytherapy, including single-seed insertion.

Methods:

First, the impact of the energy dependence of plastic scintillation detectors (PSDs) was studied using GEANT4 Monte Carlo simulations adapted from the ALGEBRA source code for brachytherapy. The photon energy spectrum was obtained in water around an I-125 brachytherapy seed and convoluted to a detector response. Secondly, because low dose rate results in a corresponding low light emission, another part of this study focused on optimizing the choice of each component of the system to enhance the signal-to-noise ratio. A novel motorized and automated PSD positioning device mounted to a water tank was also developed to minimize uncertainties. Measurements of 15s were performed for distances from 1 cm to 7 cm in different radial and longitudinal directions and compared to the expected values.

Results:

Even though the photon energy spectrum around the I-125 source was shown to vary considerably, the effect on dose measurement accuracy was minor (<1%). This holds true as long as the PSD is calibrated using the same brachytherapy isotope. The different components of the PSD probe did not show a significant effect on the calculated spectrum (<0.1%). Proper selection of photodetector and optical components helped improving by over 35X the signal-to-noise ratio. The measurements agreed with the expected values in all conditions. The PSD system was shown capable of detecting source misplacements for all clinically relevant conditions of measurement.

Conclusion:

The system developed in this study allows for accurate dose measurements around an I-125 seed and could therefore provide valuable information in real-time during LDR brachytherapy seed implant.

Part of this research was supported by the Odyssey Program at The University of Texas MD Anderson Cancer Center.

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