Simulation evaluation of NIST air-kerma rate calibration standard for electronic brachytherapy.

摘要: Purpose: Dosimetry for the model S700 50 kV electronic brachytherapy (eBT) source (Xoft, Inc., a subsidiary of iCAD, San Jose, CA) was simulated using Monte Carlo(MC) methods by Rivard et al. [“Calculated and measuredbrachytherapydosimetry parameters in water Xoft Axxent x-ray source: An source,” Med. Phys. 33, 4020–4032 (2006)] recently Hiatt [“A revised dosimetric characterization containing an anode-centering plastic insert other components not included 2006 model,” 42, 2764–2776 (2015)] with improved geometric characterization. While these studies examined dose distribution water, there have previously been reports eBT calibration beyond that reported Seltzer [“New national air-kerma standard low-energy sources,” J. Res. Natl. Inst. Stand. Technol. 119, 554–574 (2014)]. Therefore, motivation current study to provide independent determination rate at cm air K ( d = ) MC source. Methods: Using CAD information provided vendor disassembled sources, created Simulations were run mcnp6radiation transport code NIST Lamperti ionization chamber according specifications Boutillon [“Comparison exposure standards 10-50 region,” Metrologia 5, 1–11 (1969)], without chamber, vacuum chamber. determined *F4 tally values mass energy-absorption coefficients air. Photon spectra evaluated over 2π azimuthal sampling polar angles 0° ≤ θ 180° every 1°. Volume averaging averted through tight radial binning. energy all both F4 0.1 keV resolution. A total 1011 histories geometry (statistical uncertainty 0.14%), 1010 in-air in-vacuum simulations 0.04%). The calculated amounted 6.8%. Results: from modeled be (1.850 ± 0.126) × 10−4 Gy/s, which within range (1.67–2.11) Gy/s measured NIST. ratio photon good agreement above 13 keV, < 150° where influence Kovar sleeve Ag epoxy caused increased scatter Below exhibited decrease attributed attenuation photons Across most on transverse plane, between authors’ Discrepancies observed 40 spectrum had steeper fall-off towards keV. Conclusions: Through radiation transport, this validation source, mean results 3.3%. This difference smaller than (i.e., 23%) values.