Direct energy spectrum measurement of X‐ray from a clinical linac

Abstract

A realistic X‐ray energy spectrum is essential for accurate dose calculation using the Monte Carlo (MC) algorithm. An energy spectrum for dose calculation in the radiation treatment planning system is modeled using the MC algorithm and adjusted to obtain acceptable agreement with the measured percent depth dose (PDD) and off‐axis ratio. The simulated energy spectrum may not consistently reproduce a realistic energy spectrum. Therefore, direct measurement of the X‐ray energy spectrum from a linac is necessary to obtain a realistic spectrum. Previous studies have measured low photon fluence directly, but the measurement was performed with a nonclinical linac with a thick target and a long target‐to‐detector distance. In this study, an X‐ray energy spectrum from a clinical linac was directly measured using a NaI(Tl) scintillator at an ultralow dose rate achieved by adjusting the gun grid voltage. The measured energy spectrum was unfolded by the Gold algorithm and compared with a simulated spectrum using statistical tests. Furthermore, the PDD was calculated using an unfolded energy spectrum and a simulated energy spectrum was compared with the measured PDD to evaluate the validity of the unfolded energy spectrum. Consequently, there was no significant difference between the unfolded and simulated energy spectra by nonparametric, Wilcoxon's rank‐sum, chi‐square, and two‐sample Kolmogorov–Smirnov tests with a significance level of 0.05. However, the PDD calculated from the unfolded energy spectrum better agreed with the measured compared to the calculated PDD results from the simulated energy spectrum. The adjustment of the incident electron parameters using MC simulation is sensitive and takes time. Therefore, it is desirable to obtain the energy spectrum by direct measurement. Thus, a method to obtain the realistic energy spectrum by direct measurement was proposed in this study.

Relative dose-response from solid-state and gel dosimeters through Monte Carlo simulations

“…Comparing these curves can help validate the conditions used in this work. Figures 2 and 3 show the PDD curves for energies of 6 MV and Figures 2 and 3 show that both simulation codes reproduce the experimental data with a difference of less than 2% for 6 MV; this difference is comparable to Marioti et al [18] and Suda et al [70]. For 250 kV photon beam, the difference from 3.3% to 5.5% for PENELOPE code and 2.2% to 3.2% for MCNPX were found at depths between 6 and 11 cm, relative to experimental data.…”

Monte Carlo Simulation‐Guided Design of a Thorium‐Based Metal–Organic Framework for Efficient Radiotherapy‐Radiodynamic Therapy

“…We posited that, as the heaviest naturally occurring element with low radioactivity (Z=90 and half‐life of the major isotope 232 Th=14 billion years), Th could serve as an ideal element for constructing nMOF radiosensitizers. In particular, the higher K‐edge energy of Th (110 keV) over that of Hf (65 keV, Figure S1) makes Th more suitable for clinically relevant megavoltage beams from linear particle accelerators and 60 Co sources [35, 36] . Here, we report Monte Carlo simulation‐guided design of a Th‐DBP nMOF based on Th 6 O 4 (OH) 4 SBUs and photosensitizing DBP ligands (DBP=5,15‐di(p‐benzoato)porphyrin) for efficient RT‐RDT.…”

“…In particular, the higher K-edge energy of Th (110 keV) over that of Hf (65 keV, Figure S1) makes Th more suitable for clinically relevant megavoltage beams from linear particle accelerators and 60 Co sources. [35,36] Here, we report Monte Carlo simulation-guided design of a Th-DBP nMOF based on Th 6 O 4 (OH) 4 SBUs and photosensitizing DBP ligands (DBP = 5,15-di(p-benzoato)porphyrin) for efficient RT-RDT. Under X-ray or γ-ray irradiation, the electron-dense Th 6 SBUs effectively interact with photons and generate hydroxyl radicals while exciting the photosensitizing DBP ligands to generate 1 O 2 .…”