skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: SU-E-T-165: Evaluation of Inhomogeneity Calculations for Electron Beams in Raystation Monte Carlo Algorithm

Abstract

Purpose: To evaluate the accuracy of the Raystation electron Monte Carlo algorithm for bone and air inhomogeneity. Methods: A solid water phantom slab was drilled to contain two openings of 1.3cm diameter, 0.6cm apart. The center of the opening is at 1cm depth from the surface. Two Teflon rods of exact same diameter were inserted to investigate bone inhomogeneity. Slab is 2cm total in thickness and was placed on top of 10cm solid water. Plans were created in Raystation with clinical settings previously established for 6, 9, 12, 15 and 18MeV Elekta Infinity beams. Coronal profiles were extracted posteriorly to the inhomogeneity. EBT3 films were irradiated under the same conditions and analyzed using FilmQAPro using the red channel. Calibration films were used for all energies. Same plans and films were performed for a Varian accelerator with same energies and Eclipse Monte Carlo. Results: Air Inhomogeneities: For lower energies, Raystation- Film agreement is less than 1% for the regions of the air cavity. In the lateral interface border, Raystation underestimates dose by approximately 2%. Eclipse results are similar. For higher energies, Raystation-Film agreement remains the same across the air cavity and interface. Eclipse-Film difference increases with energy up to 5% formore » 18MeV, with Eclipse calculating higher doses than the film at the interface. Bone Inhomogeneities: For lower energies, Raystation underestimates the dose behind the bone up to 12%. Eclipse underestimates the dose in the same area up to 18%. For higher energies, the dose difference behind the bone decreases to 1% for Raystation and 3% for Eclipse. At the lateral interface, Raystation underestimates the dose by 2.2% and Eclipse underestimates the dose by 5%. Conclusion: Raystation prediction for air and bone is acceptable. Maximum deviations are consistent with algorithm limitations. Differences between calculations and measurement are closer for Raystation than for Eclipse.« less

Authors:
; ;  [1]
  1. Health-quest, Poughkeepsie, NY (United States)
Publication Date:
OSTI Identifier:
22339913
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 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; ALGORITHMS; ELECTRON BEAMS; EVALUATION; MONTE CARLO METHOD; PHANTOMS; RADIATION DOSES; SKELETON; TEFLON

Citation Formats

Sansourekidou, P, Allen, C, and Pavord, D. SU-E-T-165: Evaluation of Inhomogeneity Calculations for Electron Beams in Raystation Monte Carlo Algorithm. United States: N. p., 2014. Web. doi:10.1118/1.4888494.
Sansourekidou, P, Allen, C, & Pavord, D. SU-E-T-165: Evaluation of Inhomogeneity Calculations for Electron Beams in Raystation Monte Carlo Algorithm. United States. doi:10.1118/1.4888494.
Sansourekidou, P, Allen, C, and Pavord, D. Sun . "SU-E-T-165: Evaluation of Inhomogeneity Calculations for Electron Beams in Raystation Monte Carlo Algorithm". United States. doi:10.1118/1.4888494.
@article{osti_22339913,
title = {SU-E-T-165: Evaluation of Inhomogeneity Calculations for Electron Beams in Raystation Monte Carlo Algorithm},
author = {Sansourekidou, P and Allen, C and Pavord, D},
abstractNote = {Purpose: To evaluate the accuracy of the Raystation electron Monte Carlo algorithm for bone and air inhomogeneity. Methods: A solid water phantom slab was drilled to contain two openings of 1.3cm diameter, 0.6cm apart. The center of the opening is at 1cm depth from the surface. Two Teflon rods of exact same diameter were inserted to investigate bone inhomogeneity. Slab is 2cm total in thickness and was placed on top of 10cm solid water. Plans were created in Raystation with clinical settings previously established for 6, 9, 12, 15 and 18MeV Elekta Infinity beams. Coronal profiles were extracted posteriorly to the inhomogeneity. EBT3 films were irradiated under the same conditions and analyzed using FilmQAPro using the red channel. Calibration films were used for all energies. Same plans and films were performed for a Varian accelerator with same energies and Eclipse Monte Carlo. Results: Air Inhomogeneities: For lower energies, Raystation- Film agreement is less than 1% for the regions of the air cavity. In the lateral interface border, Raystation underestimates dose by approximately 2%. Eclipse results are similar. For higher energies, Raystation-Film agreement remains the same across the air cavity and interface. Eclipse-Film difference increases with energy up to 5% for 18MeV, with Eclipse calculating higher doses than the film at the interface. Bone Inhomogeneities: For lower energies, Raystation underestimates the dose behind the bone up to 12%. Eclipse underestimates the dose in the same area up to 18%. For higher energies, the dose difference behind the bone decreases to 1% for Raystation and 3% for Eclipse. At the lateral interface, Raystation underestimates the dose by 2.2% and Eclipse underestimates the dose by 5%. Conclusion: Raystation prediction for air and bone is acceptable. Maximum deviations are consistent with algorithm limitations. Differences between calculations and measurement are closer for Raystation than for Eclipse.},
doi = {10.1118/1.4888494},
journal = {Medical Physics},
number = 6,
volume = 41,
place = {United States},
year = {Sun Jun 01 00:00:00 EDT 2014},
month = {Sun Jun 01 00:00:00 EDT 2014}
}
  • Purpose: To evaluate the Raystation v4.51 Electron Monte Carlo algorithm for Varian Trilogy, IX and 2100 series linear accelerators and commission for clinical use. Methods: Seventy two water and forty air scans were acquired with a water tank in the form of profiles and depth doses, as requested by vendor. Data was imported into Rayphysics beam modeling module. Energy spectrum was modeled using seven parameters. Contamination photons were modeled using five parameters. Source phase space was modeled using six parameters. Calculations were performed in clinical version 4.51 and percent depth dose curves and profiles were extracted to be compared tomore » water tank measurements. Sensitivity tests were performed for all parameters. Grid size and particle histories were evaluated per energy for statistical uncertainty performance. Results: Model accuracy for air profiles is poor in the shoulder and penumbra region. However, model accuracy for water scans is acceptable. All energies and cones are within 2%/2mm for 90% of the points evaluated. Source phase space parameters have a cumulative effect. To achieve distributions with satisfactory smoothness level a 0.1cm grid and 3,000,000 particle histories were used for commissioning calculations. Calculation time was approximately 3 hours per energy. Conclusion: Raystation electron Monte Carlo is acceptable for clinical use for the Varian accelerators listed. Results are inferior to Elekta Electron Monte Carlo modeling. Known issues were reported to Raysearch and will be resolved in upcoming releases. Auto-modeling is limited to open cone depth dose curves and needs expansion.« less
  • Purpose: This study evaluated the performance of the electron Monte Carlo dose calculation algorithm in RayStation v4.0 for an Elekta machine with Agility™ treatment head. Methods: The machine has five electron energies (6–8 MeV) and five applicators (6×6 to 25×25 cm {sup 2}). The dose (cGy/MU at d{sub max}), depth dose and profiles were measured in water using an electron diode at 100 cm SSD for nine square fields ≥2×2 cm{sup 2} and four complex fields at normal incidence, and a 14×14 cm{sup 2} field at 15° and 30° incidence. The dose was also measured for three square fields ≥4×4more » cm{sup 2} at 98, 105 and 110 cm SSD. Using selected energies, the EBT3 radiochromic film was used for dose measurements in slab-shaped inhomogeneous phantoms and a breast phantom with surface curvature. The measured and calculated doses were analyzed using a gamma criterion of 3%/3 mm. Results: The calculated and measured doses varied by <3% for 116 of the 120 points, and <5% for the 4×4 cm{sup 2} field at 110 cm SSD at 9–18 MeV. The gamma analysis comparing the 105 pairs of in-water isodoses passed by >98.1%. The planar doses measured from films placed at 0.5 cm below a lung/tissue layer (12 MeV) and 1.0 cm below a bone/air layer (15 MeV) showed excellent agreement with calculations, with gamma passing by 99.9% and 98.5%, respectively. At the breast-tissue interface, the gamma passing rate is >98.8% at 12–18 MeV. The film results directly validated the accuracy of MU calculation and spatial dose distribution in presence of tissue inhomogeneity and surface curvature - situations challenging for simpler pencil-beam algorithms. Conclusion: The electron Monte Carlo algorithm in RayStation v4.0 is fully validated for clinical use for the Elekta Agility™ machine. The comprehensive validation included small fields, complex fields, oblique beams, extended distance, tissue inhomogeneity and surface curvature.« less
  • Purpose: To evaluate the Raystation v4.0 Electron Monte Carlo algorithm for an Elekta Infinity linear accelerator and commission for clinical use. Methods: A total of 199 tests were performed (75 Export and Documentation, 20 PDD, 30 Profiles, 4 Obliquity, 10 Inhomogeneity, 55 MU Accuracy, and 5 Grid and Particle History). Export and documentation tests were performed with respect to MOSAIQ (Elekta AB) and RadCalc (Lifeline Software Inc). Mechanical jaw parameters and cutout magnifications were verified. PDD and profiles for open cones and cutouts were extracted and compared with water tank measurements. Obliquity and inhomogeneity for bone and air calculations weremore » compared to film dosimetry. MU calculations for open cones and cutouts were performed and compared to both RadCalc and simple hand calculations. Grid size and particle histories were evaluated per energy for statistical uncertainty performance. Acceptability was categorized as follows: performs as expected, negligible impact on workflow, marginal impact, critical impact or safety concern, and catastrophic impact of safety concern. Results: Overall results are: 88.8% perform as expected, 10.2% negligible, 2.0% marginal, 0% critical and 0% catastrophic. Results per test category are as follows: Export and Documentation: 100% perform as expected, PDD: 100% perform as expected, Profiles: 66.7% perform as expected, 33.3% negligible, Obliquity: 100% marginal, Inhomogeneity 50% perform as expected, 50% negligible, MU Accuracy: 100% perform as expected, Grid and particle histories: 100% negligible. To achieve distributions with satisfactory smoothness level, 5,000,000 particle histories were used. Calculation time was approximately 1 hour. Conclusion: Raystation electron Monte Carlo is acceptable for clinical use. All of the issues encountered have acceptable workarounds. Known issues were reported to Raysearch and will be resolved in upcoming releases.« less
  • Purpose: To evaluate the Eclipse electron Monte Carlo (eMC) algorithm based on patient specific monitor unit (MU) calculations, and to propose a new factor which quantitatively predicts the discrepancy of MUs between the eMC algorithm and hand calculations. Methods: Electron treatments were planned for 61 patients on Eclipse (Version 10.0) using the eMC algorithm for Varian TrueBeam linear accelerators. For each patient, the same treatment beam angle was kept for a point dose calculation at dmax performed with the reference condition, which used an open beam with a 15×15 cm2 size cone and 100 SSD. A patient specific correction factormore » (PCF) was obtained by getting the ratio between this point dose and the calibration dose, which is 1 cGy per MU delivered at dmax. The hand calculation results were corrected by the PCFs and compared with MUs from the treatment plans. Results: The MU from the treatment plans were in average (7.1±6.1)% higher than the hand calculations. The average MU difference between the corrected hand calculations and the eMC treatment plans was (0.07±3.48)%. A correlation coefficient of 0.8 was found between (1-PCF) and the percentage difference between the treatment plan and hand calculations. Most outliers were treatment plans with small beam opening (< 4 cm) and low energy beams (6 and 9 MeV). Conclusion: For CT-based patient treatment plans, the eMC algorithm tends to generate a larger MU than hand calculations. Caution should be taken for eMC patient plans with small field sizes and low energy beams. We hypothesize that the PCF ratio reflects the influence of patient surface curvature and tissue inhomogeneity to patient specific percent depth dose (PDD) curve and MU calculations in eMC algorithm.« less
  • 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 reducemore » 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.« less