A phantom study for in-vivo dosimetry of high dose rate brachytherapy applicators

Abstract

Purpose: The aim of the current investigation was to calibrate the diode in-vivo dosimetry (IVD) system for high-dose-rate (HDR) brachytherapy and to design a phantom study for in-vivo dosimetry of HDR brachytherapy applicators. Methods: Gamma Med Plus with Abacus 3.1 treatment planning system (TPS), and diode dosimetry system has been used in this study. Calibration and different correction factors of diode have been measured in water phantom. Treatment simulation, planning of different applicators for esophagus, rectum/vagina and cervix (fletcher & ring), dose delivery and finally in-vivo verification at prescription point using diode in water phantom has been performed. Results: The mean calibration factor for diode for Ir-192 HDR source is 1.256 (N=15) with σ ± 0.0015. The overall average percentage difference between TPS dose and diode dose was 1.87% (σ ± 2.64) for all measurements, 1.86% (σ ± 2.73) for esophagus, 1.86% (σ± 2.94) for rectum/vagina and 1.67% (σ ±2.81) for fletcher and 2.07% (σ ± 2.26) for ring applicators, respectively. These results advocate that the dose calculated by TPS and dose measured using diode for the various clinical situations deliberated here are in good agreement (~2%) at the points of clinical importance. Conclusion: The in-vivo phantom dosimetry study gives both a confidence that the treatments are being delivered as prescribed and enhance the reliability of the HDR brachytherapy treatment. This may be used for acceptance testing/commissioning of new treatment planning system and to validate the new brachytherapy techniques in the clinics.