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Title: SU-F-T-679: Monte Carlo Simulation On Surface Dose in Preclinical Irradiation Using Monoenergetic Photon Beams

Abstract

Purpose: This study investigated the surface dose variation in preclinical irradiation using small animal, when monoenergetic photon beams with energy range from 50 keV to 1.25 MeV were used. Methods: Inhomogeneous, homogeneous and bone-tissue homogeneous mouse phantom based on the same CT image set were used. The homogeneous and bone-tissue homogeneous phantom were created with the relative electron density of all and only bone voxels of the mouse overridden to one, respectively. Monte Carlo simulation based on the EGSnrc-based code was used to calculate the surface dose, when the phantoms were irradiated by a 360° photon arc with energies ranging from 50 keV to 1.25 MeV. The mean surface doses of the three phantoms were calculated. In addition, the surface doses from partial arcs, 45°–315°, 125°–225°, 45°–125° and 225°–315° covering the anterior, posterior, right lateral and left lateral region of the mouse were determined using different photon beam energies. Results: When the prescribed dose at the isocenter of the mouse was 2 Gy, the maximum mean surface doses, found at the 50-keV photon beams, were 0.358 Gy, 0.363 Gy and 0.350 Gy for the inhomogeneous, homogeneous and bone-tissue homogeneous mouse phantom, respectively. The mean surface dose of the mouse wasmore » found decreasing with an increase of the photon beam energy. For surface dose in different orientations, the lateral regions of the mouse were receiving lower dose than the anterior and posterior regions. This may be due to the increase of beam attenuation along the horizontal (left-right) axis than the vertical (anterior-posterior) in the mouse. Conclusion: It is concluded that consideration of phantom inhomogeneity in the dose calculation resulted in a lower mean surface dose of the mouse. The mean surface dose also decreased with an increase of photon beam energy in the kilovoltage range.« less

Authors:
 [1];  [2]
  1. Michener Institute, Toronto, ON (Canada)
  2. Princess Margaret Cancer Centre, Toronto, ON (Canada)
Publication Date:
OSTI Identifier:
22649234
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; BONE TISSUES; COMPUTERIZED SIMULATION; COMPUTERIZED TOMOGRAPHY; IMAGE PROCESSING; IRRADIATION; KEV RANGE 10-100; MEV RANGE 01-10; MICE; MONTE CARLO METHOD; PHANTOMS; PHOTON BEAMS; RADIATION DOSES

Citation Formats

Vuong, A, and Chow, J. SU-F-T-679: Monte Carlo Simulation On Surface Dose in Preclinical Irradiation Using Monoenergetic Photon Beams. United States: N. p., 2016. Web. doi:10.1118/1.4956865.
Vuong, A, & Chow, J. SU-F-T-679: Monte Carlo Simulation On Surface Dose in Preclinical Irradiation Using Monoenergetic Photon Beams. United States. doi:10.1118/1.4956865.
Vuong, A, and Chow, J. 2016. "SU-F-T-679: Monte Carlo Simulation On Surface Dose in Preclinical Irradiation Using Monoenergetic Photon Beams". United States. doi:10.1118/1.4956865.
@article{osti_22649234,
title = {SU-F-T-679: Monte Carlo Simulation On Surface Dose in Preclinical Irradiation Using Monoenergetic Photon Beams},
author = {Vuong, A and Chow, J},
abstractNote = {Purpose: This study investigated the surface dose variation in preclinical irradiation using small animal, when monoenergetic photon beams with energy range from 50 keV to 1.25 MeV were used. Methods: Inhomogeneous, homogeneous and bone-tissue homogeneous mouse phantom based on the same CT image set were used. The homogeneous and bone-tissue homogeneous phantom were created with the relative electron density of all and only bone voxels of the mouse overridden to one, respectively. Monte Carlo simulation based on the EGSnrc-based code was used to calculate the surface dose, when the phantoms were irradiated by a 360° photon arc with energies ranging from 50 keV to 1.25 MeV. The mean surface doses of the three phantoms were calculated. In addition, the surface doses from partial arcs, 45°–315°, 125°–225°, 45°–125° and 225°–315° covering the anterior, posterior, right lateral and left lateral region of the mouse were determined using different photon beam energies. Results: When the prescribed dose at the isocenter of the mouse was 2 Gy, the maximum mean surface doses, found at the 50-keV photon beams, were 0.358 Gy, 0.363 Gy and 0.350 Gy for the inhomogeneous, homogeneous and bone-tissue homogeneous mouse phantom, respectively. The mean surface dose of the mouse was found decreasing with an increase of the photon beam energy. For surface dose in different orientations, the lateral regions of the mouse were receiving lower dose than the anterior and posterior regions. This may be due to the increase of beam attenuation along the horizontal (left-right) axis than the vertical (anterior-posterior) in the mouse. Conclusion: It is concluded that consideration of phantom inhomogeneity in the dose calculation resulted in a lower mean surface dose of the mouse. The mean surface dose also decreased with an increase of photon beam energy in the kilovoltage range.},
doi = {10.1118/1.4956865},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: The aim of this study is to investigate the variation of bone dose on photon beam energy (keV – MeV) in small-animal irradiation. Dosimetry of homogeneous and inhomogeneous phantoms as per the same mouse computed tomography image set were calculated using the DOSCTP and DOSXYZnrc based on the EGSnrc Monte Carlo code. Methods: Monte Carlo simulations for the homogeneous and inhomogeneous mouse phantom irradiated by a 360 degree photon arc were carried out. Mean doses of the bone tissue in the irradiated volumes were calculated at various photon beam energies, ranging from 50 keV to 1.25 MeV. The effectmore » of bone inhomogeneity was examined through the Inhomogeneous Correction Factor (ICF), a dose ratio of the inhomogeneous to the homogeneous medium. Results: From our Monte Carlo results, higher mean bone dose and ICF were found when using kilovoltage photon beams compared to megavoltage. In beam energies ranging from 50 keV to 200 keV, the bone dose was found maximum at 50 keV, and decreased significantly from 2.6 Gy to 0.55 Gy, when 2 Gy was delivered at the center of the phantom (isocenter). Similarly, the ICF were found decreasing from 4.5 to 1 when the photon beam energy was increased from 50 keV to 200 keV. Both mean bone dose and ICF remained at about 0.5 Gy and 1 from 200 keV to 1.25 MeV with insignificant variation, respectively. Conclusion: It is concluded that to avoid high bone dose in the small-animal irradiation, photon beam energy higher than 200 keV should be used with the ICF close to one, and bone dose comparable to the megavoltage beam where photoelectric effect is not dominant.« less
  • Purpose: The introduction of the TrueBeam linac platform provides access to an in-air target assembly making it possible to apply novel treatments using multiple target designs. One such novel treatment uses multiple low-Z targets to enhance surface dose replacing the use of synthetic tissue equivalent material (bolus). This treatment technique will decrease the common dosimetric and set up errors prevalent in using physical treatment accessories like bolus. The groundwork for a novel treatment beam used to enhance surface dose to within 80-100% of the dose at dmax by utilizing low-Z (Carbon) targets of various percent CSDA range thickness operated atmore » 2.5–4 MeV used in conjunction with a clinical 6 MV beam is presented herein. Methods: A standard Monte Carlo model of a Varian Clinac accelerator was developed to manufacturers specifications. Simulations were performed using Be, C, AL, and C, as potential low-Z targets, placed in the secondary target position. The results determined C to be the target material of choice. Simulations of 15, 30 and 60% CSDA range C beams were propagated through slab phantoms. The resulting PDDs were weighted and combined with a standard 6 MV treatment beam. Versions of the experimental targets were installed into a 2100C Clinac and the models were validated. Results: Carbon was shown to be the low-Z material of choice for this project. Using combinations of 15, 30, 60% CSDA beams operated at 2.5 and 4 MeV in combination with a standard 6 MV treatment beam the surface dose was shown to be enhanced to within 80–100% the dose at dmax. Conclusion: The modeled low-Z beams were successfully validated using machined versions of the targets. Water phantom measurements and slab phantom simulations show excellent correlation. Patient simulations are now underway to compare the use of bolus with the proposed novel beams. NSERC.« less
  • Purpose: This study investigated the dose enhancement due to addition of nanoparticles with different types and concentrations in skin radiotherapy using kilovoltage photon beams. Methods: An inhomogeneous water phantom (15×15×10 cm{sup 3}) having the skin target layer (0.5–5 mm), added with different concentrations (3–40 mg/ml) of nanoparticles (Au, Pt, I, Ag and Fe{sub 2}O{sub 3}), was irradiated by the 105 and 220 kVp photon beams produced by a Gulmay D3225 Orthovoltage unit. The circular cone of 5-cm diameter and source-to-surface distance of 20 cm were used. Doses in the skin target layer with and without adding the nanoparticles were calculatedmore » using Monte Carlo simulation (the EGSnrc code) through the macroscopic approach. Dose enhancement ratio (DER), defined as the ratio of dose at the target with nanoparticle addition to the dose without addition, was calculated for each type and concentration of nanoparticle in different target thickness. Results: For Au nanoparticle, DER dependence on target thickness for the 220 kVp photon beams was not significant. However, DER for Au nanoparticle was found decreasing with an increase of target thickness when the nanoparticle concentration was increased from 18 to 40 mg/ml using the 105 kVp photon beams. For nanoparticle concentration of 40 mg/ml, DER variation with target thickness was not significant for the 220 kVp photon beams, but DEF was found decreasing with the target thickness when lower energy of photon beam (105 kVp) was used. DEF was found increasing with an increase of nanoparticle concentration. The higher the DEF increasing rate, the higher the atomic number of the nanoparticle except I and Ag for the same target thickness. Conclusion: It is concluded that nanoparticle addition can result in dose enhancement in kilovoltage skin radiotherapy. Moreover, the DER is related to the photon beam energy, target thickness, atomic number and concentration of nanoparticles.« less
  • Recently, Monte Carlo (MC) calculation method has reported as the most accurate method of predicting dose distributions in radiotherapy. The MC code system (especially DOSXYZnrc) has been used to investigate the different voxel (volume elements) sizes effect on the accuracy of dose distributions. To investigate this effect on dosimetry parameters, calculations were made with three different voxel sizes. The effects were investigated with dose distribution calculations for seven voxel sizes: 1 × 1 × 0.1 cm{sup 3}, 1 × 1 × 0.5 cm{sup 3}, and 1 × 1 × 0.8 cm{sup 3}. The 1 × 10{sup 9} histories were simulated in order tomore » get statistical uncertainties of 2%. This simulation takes about 9-10 hours to complete. Measurements are made with field sizes 10 × 10 cm2 for the 6 MV photon beams with Gaussian intensity distribution FWHM 0.1 cm and SSD 100.1 cm. MC simulated and measured dose distributions in a water phantom. The output of this simulation i.e. the percent depth dose and dose profile in d{sub max} from the three sets of calculations are presented and comparisons are made with the experiment data from TTSH (Tan Tock Seng Hospital, Singapore) in 0-5 cm depth. Dose that scored in voxels is a volume averaged estimate of the dose at the center of a voxel. The results in this study show that the difference between Monte Carlo simulation and experiment data depend on the voxel size both for percent depth dose (PDD) and profile dose. PDD scan on Z axis (depth) of water phantom, the big difference obtain in the voxel size 1 × 1 × 0.8 cm{sup 3} about 17%. In this study, the profile dose focused on high gradient dose area. Profile dose scan on Y axis and the big difference get in the voxel size 1 × 1 × 0.1 cm{sup 3} about 12%. This study demonstrated that the arrange voxel in Monte Carlo simulation becomes important.« less
  • This work is intended to investigate the application and accuracy of micro-MOSFET for superficial dose measurement under clinically used MV x-ray beams. Dose response of micro-MOSFET in the build-up region and on surface under MV x-ray beams were measured and compared to Monte Carlo calculations. First, percentage-depth-doses were measured with micro-MOSFET under 6 and 10 MV beams of normal incidence onto a flat solid water phantom. Micro-MOSFET data were compared with the measurements from a parallel plate ionization chamber and Monte Carlo dose calculation in the build-up region. Then, percentage-depth-doses were measured for oblique beams at 0 deg. - 80more » deg. onto the flat solid water phantom with micro-MOSFET placed at depths of 2 cm, 1 cm, and 2 mm below the surface. Measurements were compared to Monte Carlo calculations under these settings. Finally, measurements were performed with micro-MOSFET embedded in the first 1 mm layer of bolus placed on a flat phantom and a curved phantom of semi-cylindrical shape. Results were compared to superficial dose calculated from Monte Carlo for a 2 mm thin layer that extends from the surface to a depth of 2 mm. Results were (1) Comparison of measurements with MC calculation in the build-up region showed that micro-MOSFET has a water-equivalence thickness (WET) of 0.87 mm for 6 MV beam and 0.99 mm for 10 MV beam from the flat side, and a WET of 0.72 mm for 6 MV beam and 0.76 mm for 10 MV beam from the epoxy side. (2) For normal beam incidences, percentage depth dose agree within 3%-5% among micro-MOSFET measurements, parallel-plate ionization chamber measurements, and MC calculations. (3) For oblique incidence on the flat phantom with micro-MOSFET placed at depths of 2 cm, 1 cm, and 2 mm, measurements were consistent with MC calculations within a typical uncertainty of 3%-5%. (4) For oblique incidence on the flat phantom and a curved-surface phantom, measurements with micro-MOSFET placed at 1.0 mm agrees with the MC calculation within 6%, including uncertainties of micro-MOSFET measurements of 2%-3% (1 standard deviation), MOSFET angular dependence of 3.0%-3.5%, and 1%-2% systematical error due to phantom setup geometry asymmetry. Micro-MOSFET can be used for skin dose measurements in 6 and 10 MV beams with an estimated accuracy of {+-}6%.« less