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Title: SU-E-T-632: Preliminary Study On Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculations

Abstract

Purpose: Uneven nose surfaces and air cavities underneath and the use of bolus present complexity and dose uncertainty when using a single electron energy beam to plan treatments of nose skin with a pencil beam-based planning system. This work demonstrates more accurate dose calculation and more optimal planning using energy and intensity modulated electron radiotherapy (MERT) delivered with a pMLC. Methods: An in-house developed Monte Carlo (MC)-based dose calculation/optimization planning system was employed for treatment planning. Phase space data (6, 9, 12 and 15 MeV) were used as an input source for MC dose calculations for the linac. To reduce the scatter-caused penumbra, a short SSD (61 cm) was used. Our previous work demonstrates good agreement in percentage depth dose and off-axis dose between calculations and film measurement for various field sizes. A MERT plan was generated for treating the nose skin using a patient geometry and a dose volume histogram (DVH) was obtained. The work also shows the comparison of 2D dose distributions between a clinically used conventional single electron energy plan and the MERT plan. Results: The MERT plan resulted in improved target dose coverage as compared to the conventional plan, which demonstrated a target dose deficit atmore » the field edge. The conventional plan showed higher dose normal tissue irradiation underneath the nose skin while the MERT plan resulted in improved conformity and thus reduces normal tissue dose. Conclusion: This preliminary work illustrates that MC-based MERT planning is a promising technique in treating nose skin, not only providing more accurate dose calculation, but also offering an improved target dose coverage and conformity. In addition, this technique may eliminate the necessity of bolus, which often produces dose delivery uncertainty due to the air gaps that may exist between the bolus and skin.« less

Authors:
; ; ; ;  [1]
  1. Fox Chase Cancer Center, Philadelphia, PA (United States)
Publication Date:
OSTI Identifier:
22538141
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ANIMAL TISSUES; DEPTH DOSE DISTRIBUTIONS; ELECTRON BEAMS; FILM DOSIMETRY; LINEAR ACCELERATORS; MEV RANGE 10-100; MONTE CARLO METHOD; NOSE; PHASE SPACE; RADIOTHERAPY; SKIN

Citation Formats

Jin, L, Eldib, A, Li, J, Price, R, and Ma, C. SU-E-T-632: Preliminary Study On Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculations. United States: N. p., 2015. Web. doi:10.1118/1.4924995.
Jin, L, Eldib, A, Li, J, Price, R, & Ma, C. SU-E-T-632: Preliminary Study On Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculations. United States. doi:10.1118/1.4924995.
Jin, L, Eldib, A, Li, J, Price, R, and Ma, C. Mon . "SU-E-T-632: Preliminary Study On Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculations". United States. doi:10.1118/1.4924995.
@article{osti_22538141,
title = {SU-E-T-632: Preliminary Study On Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculations},
author = {Jin, L and Eldib, A and Li, J and Price, R and Ma, C},
abstractNote = {Purpose: Uneven nose surfaces and air cavities underneath and the use of bolus present complexity and dose uncertainty when using a single electron energy beam to plan treatments of nose skin with a pencil beam-based planning system. This work demonstrates more accurate dose calculation and more optimal planning using energy and intensity modulated electron radiotherapy (MERT) delivered with a pMLC. Methods: An in-house developed Monte Carlo (MC)-based dose calculation/optimization planning system was employed for treatment planning. Phase space data (6, 9, 12 and 15 MeV) were used as an input source for MC dose calculations for the linac. To reduce the scatter-caused penumbra, a short SSD (61 cm) was used. Our previous work demonstrates good agreement in percentage depth dose and off-axis dose between calculations and film measurement for various field sizes. A MERT plan was generated for treating the nose skin using a patient geometry and a dose volume histogram (DVH) was obtained. The work also shows the comparison of 2D dose distributions between a clinically used conventional single electron energy plan and the MERT plan. Results: The MERT plan resulted in improved target dose coverage as compared to the conventional plan, which demonstrated a target dose deficit at the field edge. The conventional plan showed higher dose normal tissue irradiation underneath the nose skin while the MERT plan resulted in improved conformity and thus reduces normal tissue dose. Conclusion: This preliminary work illustrates that MC-based MERT planning is a promising technique in treating nose skin, not only providing more accurate dose calculation, but also offering an improved target dose coverage and conformity. In addition, this technique may eliminate the necessity of bolus, which often produces dose delivery uncertainty due to the air gaps that may exist between the bolus and skin.},
doi = {10.1118/1.4924995},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Purpose: Treating nose skin with an electron beam is of a substantial challenge due to uneven nose surfaces and tissue heterogeneity, and consequently could have a great uncertainty of dose accuracy on the target. This work explored the method using Monte Carlo (MC)-based energy and intensity modulated electron radiotherapy (MERT), which would be delivered with a photon MLC in a standard medical linac (Artiste). Methods: The traditional treatment on the nose skin involves the usage of a bolus, often with a single energy electron beam. This work avoided using the bolus, and utilized mixed energies of electron beams. An in-housemore » developed Monte Carlo (MC)-based dose calculation/optimization planning system was employed for treatment planning. Phase space data (6, 9, 12 and 15 MeV) were used as an input source for MC dose calculations for the linac. To reduce the scatter-caused penumbra, a short SSD (61 cm) was used. A clinical case of the nose skin, which was previously treated with a single 9 MeV electron beam, was replanned with the MERT method. The resultant dose distributions were compared with the plan previously clinically used. The dose volume histogram of the MERT plan is calculated to examine the coverage of the planning target volume (PTV) and critical structure doses. Results: The target coverage and conformality in the MERT plan are improved as compared to the conventional plan. The MERT can provide more sufficient target coverage and less normal tissue dose underneath the nose skin. Conclusion: Compared to the conventional treatment technique, using MERT for the nose skin treatment has shown the dosimetric advantages in the PTV coverage and conformality. In addition, this technique eliminates the necessity of the cutout and bolus, which makes the treatment more efficient and accurate.« 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
  • 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: In intensity modulated proton therapy (IMPT), energy dependent, protons per monitor unit (MU) calibration factors are important parameters that determine absolute dose values from energy deposition data obtained from Monte Carlo (MC) simulations. Purpose of this study was to assess the sensitivity of MC-computed absolute dose distributions to the protons/MU calibration factors in IMPT. Methods: A “verification plan” (i.e., treatment beams applied individually to water phantom) of a head and neck patient plan was calculated using MC technique. The patient plan had three beams; one posterior-anterior (PA); two anterior oblique. Dose prescription was 66 Gy in 30 fractions. Ofmore » the total MUs, 58% was delivered in PA beam, 25% and 17% in other two. Energy deposition data obtained from the MC simulation were converted to Gy using energy dependent protons/MU calibrations factors obtained from two methods. First method is based on experimental measurements and MC simulations. Second is based on hand calculations, based on how many ion pairs were produced per proton in the dose monitor and how many ion pairs is equal to 1 MU (vendor recommended method). Dose distributions obtained from method one was compared with those from method two. Results: Average difference of 8% in protons/MU calibration factors between method one and two converted into 27 % difference in absolute dose values for PA beam; although dose distributions preserved the shape of 3D dose distribution qualitatively, they were different quantitatively. For two oblique beams, significant difference in absolute dose was not observed. Conclusion: Results demonstrate that protons/MU calibration factors can have a significant impact on absolute dose values in IMPT depending on the fraction of MUs delivered. When number of MUs increases the effect due to the calibration factors amplify. In determining protons/MU calibration factors, experimental method should be preferred in MC dose calculations. Research supported by National Cancer Institute grant P01CA021239.« less
  • Purpose: Pencil-beam or superposition-convolution type dose calculation algorithms are routinely used in inverse plan optimization for intensity modulated radiation therapy (IMRT). However, due to their limited accuracy in some challenging cases, e.g. lung, the resulting dose may lose its optimality after being recomputed using an accurate algorithm, e.g. Monte Carlo (MC). It is the objective of this study to evaluate the feasibility and advantages of a new method to include MC in the treatment planning process. Methods: We developed a scheme to iteratively perform MC-based beamlet dose calculations and plan optimization. In the MC stage, a GPU-based dose engine wasmore » used and the particle number sampled from a beamlet was proportional to its optimized fluence from the previous step. We tested this scheme in four lung cancer IMRT cases. For each case, the original plan dose, plan dose re-computed by MC, and dose optimized by our scheme were obtained. Clinically relevant dosimetric quantities in these three plans were compared. Results: Although the original plan achieved a satisfactory PDV dose coverage, after re-computing doses using MC method, it was found that the PTV D95% were reduced by 4.60%–6.67%. After re-optimizing these cases with our scheme, the PTV coverage was improved to the same level as in the original plan, while the critical OAR coverages were maintained to clinically acceptable levels. Regarding the computation time, it took on average 144 sec per case using only one GPU card, including both MC-based beamlet dose calculation and treatment plan optimization. Conclusion: The achieved dosimetric gains and high computational efficiency indicate the feasibility and advantages of the proposed MC-based IMRT optimization method. Comprehensive validations in more patient cases are in progress.« less