Measurement of the Energy Spectrum of a 6 MV Linear Accelerator Using Compton Scattering Spectroscopy and Monte Carlo-Generated Corrections

Abstract

Purpose: The energy spectrum of a linear accelerator used for dose calculations is determined during beam commissioning by iteratively adjusting the spectrum and comparing calculated and measured percent depth-dose curves. Direct measurement of the energy spectrum using pulse mode detectors is particularly challenging because of the high-energy, high fluence nature of these beams and limitations of the detector systems. This work implements a Compton scattering (CS) spectroscopy setup and presents detector corrections and spectral unfolding techniques to measure the spectrum of a 6 MV linear accelerator using a pulse mode detector. Methods: Spectral measurements were performed using a Varian Clinac 21EX linear accelerator and a high-purity germanium (HPGe) detector. To reduce fluence to the detector, a custom-built lead shield and a CS spectrometry setup were used. The detector was placed at CS angles of 46˚, 89˚, and 125˚. At each of these locations, a detector response function was generated to account for photon interactions within the experimental geometry. Gold's deconvolution algorithm was used to unfold the energy spectrum. The measured spectra were compared to simulated spectra, which were obtained using an experimentally benchmarked model of the Clinac 21EX in MCNP6. Results: Measurements were acquired and detector response corrections were calculated for all three CS angles. A comparison of spectra for all CS angles showed good agreement with one another. The spectra for all three angles were averaged and showed good agreement with the MCNP6 simulated spectrum, with all points above 400 keV falling within 4%, which was within the uncertainty of the measurement and statistical uncertainty. Conclusions: The measurement of the energy spectrum of a 6 MV linear accelerator using a pulse-mode detector is pre-

Monte Carlo Modeling and Verification of 6 MV Linear Accelerator

“…BEAMnrc and DOSXYZnrc are built on the EGSnrc Code System for modelling radiotherapy sources and calculating dose distributions responsibility [2]. The consistency between the model beam and the actual beam was verified according to percentage depth dose [3] (PDD) and lateral dose profile. A new process for adjusting the energy and full-width half-maximum (FWHM) of incident electron beam and flattening filter to fit the percentage depth dose curve as well as the beam profiles was proposed.…”

Determinación de coeficientes de dispersión en paciente y curvas de atenuación de dosis para haces de acelerador de 4 y 6 MV

“…. [56], [57] y [58] que fueron normalizados al pico correspondiente para utilizarse en el presente trabajo. .…”