Dosimetric characterization for the flat-panel x-ray source: An electronic brachytherapy unit.

Background: The flat-panel x-ray source (FPXS) is an innovative x-ray source comprising millions of micro sources that emit low-energy x-rays. To date, the dosimetric characteristics of FPXS remain unclear, limiting its clinical applications.

Purpose: This study aims to characterize the physical and dosimetric characteristics of FPXS through Monte Carlo (MC) dose calculation and experimental dosimetry measurements and to analyze the feasibility of FPXS as an electronic brachytherapy (EB) unit.

Methods: A measurement setup and two specialized measurement platforms were developed. By using an energy spectrometer, ionization chamber, and Gafchromic film, a measurement procedure for physical beam characteristics and dosimetric characteristics of FPXS was established, and a series of experimental measurements were conducted. A previously in-house developed MC simulation toolkit, designated gFPDMC, was employed to perform FPXS structure simulation and parallel dose calculation. The measured dose distributions were compared with the gFPDMC-calculated dose distributions, thereby validating the accuracy of gFPDMC.

Results: The measured energy spectra are consistent with the MC-simulated spectra with mean relative error (MRE) values < 9% and an average energy difference < 1.40%. The measured surface dose rate of FPXS increases exponentially with the operating voltage, with a maximum dose rate of 2.45 Gy/min at 40 kV; the depth dose rate decreases exponentially with the measurement depth and increases with the operating voltage. The doses calculated by gFPDMC, DOSXYZnrc, and Geant4 exhibit excellent consistency, with mean absolute error (MAE) values of 0.31% and 0.40%. The gFPDMC-calculated percentage depth dose (PDDs) exhibit identical voltage-dependent depth dose characteristics as measured PDDs, with deviations < 4%.

Conclusions: The precision of gFPDMC was rigorously validated through comparison with DOSXYZnrc, Geant4, and experimentally measured dose. Adequate operating voltage and suitable dose rate demonstrate the feasibility of FPXS as an EB unit.