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Title: SU-F-T-230: A Simple Method to Assess Accuracy of Dynamic Wave Arc Irradiation Using An Electronic Portal Imaging Device and Log Files

Abstract

Purpose: The Dynamic Wave Arc (DWA) technique, where the multi-leaf collimator (MLC) and gantry/ring move simultaneously in a predefined non-coplanar trajectory, has been developed on the Vero4DRT. The aim of this study is to develop a simple method for quality assurance of DWA delivery using an electronic portal imaging device (EPID) measurements and log files analysis. Methods: The Vero4DRT has an EPID on the beam axis, the resolution of which is 0.18 mm/pixel at the isocenter plane. EPID images were acquired automatically. To verify the detection accuracy of the MLC position by EPID images, the MLC position with intentional errors was assessed. Tests were designed considering three factors: (1) accuracy of the MLC position (2) dose output consistency with variable dose rate (160–400 MU/min), gantry speed (2.4–6°/s), ring speed (0.5–2.5°/s), and (3) MLC speed (1.6–4.2 cm/s). All the patterns were delivered to the EPID and compared with those obtained with a stationary radiation beam with a 0° gantry angle. The irradiation log, including the MLC position and gantry/ring angle, were recorded simultaneously. To perform independent checks of the machine accuracy, the MLC position and gantry/ring angle position were assessed using log files. Results: 0.1 mm intentional error can be detectedmore » by the EPID, which is smaller than the EPID pixel size. The dose outputs with different conditions of the dose rate and gantry/ring speed and MLC speed showed good agreement, with a root mean square (RMS) error of 0.76%. The RMS error between the detected and recorded data were 0.1 mm for the MLC position, 0.12° for the gantry angle, and 0.07° for the ring angle. Conclusion: The MLC position and dose outputs in variable conditions during DWA irradiation can be easily detected using EPID measurements and log file analysis. The proposed method is useful for routine verification. This research is (partially) supported by the Practical Research for Innovative Cancer Control (15Ack0106151h0001) from Japan Agency for Medical Research and development, AMED. Authors Takashi Mizowaki and Masahiro Hiraoka have consultancy agreement with Mitsubishi Heavy Industries, Ltd., Japan.« less

Authors:
; ; ; ; ; ;  [1]
  1. Kyoto University, Graduate School of Medicine, Kyoto, Kyoto (Japan)
Publication Date:
OSTI Identifier:
22648846
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; ACCURACY; BIOMEDICAL RADIOGRAPHY; DOSE RATES; EQUIPMENT; ERRORS; IMAGES; IRRADIATION; QUALITY ASSURANCE

Citation Formats

Hirashima, H, Miyabe, Y, Yokota, K, Nakamura, M, Mukumoto, N, Mizowaki, T, and Hiraoka, M. SU-F-T-230: A Simple Method to Assess Accuracy of Dynamic Wave Arc Irradiation Using An Electronic Portal Imaging Device and Log Files. United States: N. p., 2016. Web. doi:10.1118/1.4956369.
Hirashima, H, Miyabe, Y, Yokota, K, Nakamura, M, Mukumoto, N, Mizowaki, T, & Hiraoka, M. SU-F-T-230: A Simple Method to Assess Accuracy of Dynamic Wave Arc Irradiation Using An Electronic Portal Imaging Device and Log Files. United States. doi:10.1118/1.4956369.
Hirashima, H, Miyabe, Y, Yokota, K, Nakamura, M, Mukumoto, N, Mizowaki, T, and Hiraoka, M. 2016. "SU-F-T-230: A Simple Method to Assess Accuracy of Dynamic Wave Arc Irradiation Using An Electronic Portal Imaging Device and Log Files". United States. doi:10.1118/1.4956369.
@article{osti_22648846,
title = {SU-F-T-230: A Simple Method to Assess Accuracy of Dynamic Wave Arc Irradiation Using An Electronic Portal Imaging Device and Log Files},
author = {Hirashima, H and Miyabe, Y and Yokota, K and Nakamura, M and Mukumoto, N and Mizowaki, T and Hiraoka, M},
abstractNote = {Purpose: The Dynamic Wave Arc (DWA) technique, where the multi-leaf collimator (MLC) and gantry/ring move simultaneously in a predefined non-coplanar trajectory, has been developed on the Vero4DRT. The aim of this study is to develop a simple method for quality assurance of DWA delivery using an electronic portal imaging device (EPID) measurements and log files analysis. Methods: The Vero4DRT has an EPID on the beam axis, the resolution of which is 0.18 mm/pixel at the isocenter plane. EPID images were acquired automatically. To verify the detection accuracy of the MLC position by EPID images, the MLC position with intentional errors was assessed. Tests were designed considering three factors: (1) accuracy of the MLC position (2) dose output consistency with variable dose rate (160–400 MU/min), gantry speed (2.4–6°/s), ring speed (0.5–2.5°/s), and (3) MLC speed (1.6–4.2 cm/s). All the patterns were delivered to the EPID and compared with those obtained with a stationary radiation beam with a 0° gantry angle. The irradiation log, including the MLC position and gantry/ring angle, were recorded simultaneously. To perform independent checks of the machine accuracy, the MLC position and gantry/ring angle position were assessed using log files. Results: 0.1 mm intentional error can be detected by the EPID, which is smaller than the EPID pixel size. The dose outputs with different conditions of the dose rate and gantry/ring speed and MLC speed showed good agreement, with a root mean square (RMS) error of 0.76%. The RMS error between the detected and recorded data were 0.1 mm for the MLC position, 0.12° for the gantry angle, and 0.07° for the ring angle. Conclusion: The MLC position and dose outputs in variable conditions during DWA irradiation can be easily detected using EPID measurements and log file analysis. The proposed method is useful for routine verification. This research is (partially) supported by the Practical Research for Innovative Cancer Control (15Ack0106151h0001) from Japan Agency for Medical Research and development, AMED. Authors Takashi Mizowaki and Masahiro Hiraoka have consultancy agreement with Mitsubishi Heavy Industries, Ltd., Japan.},
doi = {10.1118/1.4956369},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: Fast and accurate transit portal dosimetry was investigated by developing a density-scaled layer model of electronic portal imaging device (EPID) and applying it to a clinical environment. Methods: The model was developed for fast Monte Carlo dose calculation. The model was validated through comparison with measurements of dose on EPID using first open beams of varying field sizes under a 20-cm-thick flat phantom. After this basic validation, the model was further tested by applying it to transit dosimetry and dose reconstruction that employed our predetermined dose-response-based algorithm developed earlier. The application employed clinical intensity-modulated beams irradiated on a Randomore » phantom. The clinical beams were obtained through planning on pelvic regions of the Rando phantom simulating prostate and large pelvis intensity modulated radiation therapy. To enhance agreement between calculations and measurements of dose near penumbral regions, convolution conversion of acquired EPID images was alternatively used. In addition, thickness-dependent image-to-dose calibration factors were generated through measurements of image and calculations of dose in EPID through flat phantoms of various thicknesses. The factors were used to convert acquired images in EPID into dose. Results: For open beam measurements, the model showed agreement with measurements in dose difference better than 2% across open fields. For tests with a Rando phantom, the transit dosimetry measurements were compared with forwardly calculated doses in EPID showing gamma pass rates between 90.8% and 98.8% given 4.5 mm distance-to-agreement (DTA) and 3% dose difference (DD) for all individual beams tried in this study. The reconstructed dose in the phantom was compared with forwardly calculated doses showing pass rates between 93.3% and 100% in isocentric perpendicular planes to the beam direction given 3 mm DTA and 3% DD for all beams. On isocentric axial planes, the pass rates varied between 95.8% and 99.9% for all individual beams and they were 98.2% and 99.9% for the composite beams of the small and large pelvis cases, respectively. Three-dimensional gamma pass rates were 99.0% and 96.4% for the small and large pelvis cases, respectively. Conclusions: The layer model of EPID built for Monte Carlo calculations offered fast (less than 1 min) and accurate calculation for transit dosimety and dose reconstruction.« less
  • Purpose: To develop an accurate, straightforward, and user-independent method for performing light versus radiation field coincidence quality assurance utilizing EPID images, a simple phantom made of readily-accessible materials, and a free software program. Methods: A simple phantom consisting of a blocking tray, graph paper, and high-density wire was constructed. The phantom was used to accurately set the size of a desired light field and imaged on the electronic portal imaging device (EPID). A macro written for use in ImageJ, a free image processing software, was then use to determine the radiation field size utilizing the high density wires on themore » phantom for a pixel to distance calibration. The macro also performs an analysis on the measured radiation field utilizing the tolerances recommended in the AAPM Task Group #142. To verify the accuracy of this method, radiochromic film was used to qualitatively demonstrate agreement between the film and EPID results, and an additional ImageJ macro was used to quantitatively compare the radiation field sizes measured both with the EPID and film images. Results: The results of this technique were benchmarked against film measurements, which have been the gold standard for testing light versus radiation field coincidence. The agreement between this method and film measurements were within 0.5 mm. Conclusion: Due to the operator dependency associated with tracing light fields and measuring radiation fields by hand when using film, this method allows for a more accurate comparison between the light and radiation fields with minimal operator dependency. Removing the need for radiographic or radiochromic film also eliminates a reoccurring cost and increases procedural efficiency.« less
  • Purpose: Radiotherapy patients are increasingly treated with intensity-modulated radiotherapy (IMRT) and high tumor doses. As part of our quality control program to ensure accurate dose delivery, a new method was investigated that enables the verification of the IMRT fluence delivered during patient treatment using an electronic portal imaging device (EPID), irrespective of changes in patient geometry. Methods and materials: Each IMRT treatment field is split into a static field and a modulated field, which are delivered in sequence. Images are acquired for both fields using an EPID. The portal dose image obtained for the static field is used to determinemore » changes in patient geometry between the planning CT scan and the time of treatment delivery. With knowledge of these changes, the delivered IMRT fluence can be verified using the portal dose image of the modulated field. This method, called split IMRT field technique (SIFT), was validated first for several phantom geometries, followed by clinical implementation for a number of patients treated with IMRT. Results: The split IMRT field technique allows for an accurate verification of the delivered IMRT fluence (generally within 1% [standard deviation]), even if large interfraction changes in patient geometry occur. For interfraction radiological path length changes of 10 cm, deliberately introduced errors in the delivered fluence could still be detected to within 1% accuracy. Application of SIFT requires only a minor increase in treatment time relative to the standard IMRT delivery. Conclusions: A new technique to verify the delivered IMRT fluence from EPID images, which is independent of changes in the patient geometry, has been developed. SIFT has been clinically implemented for daily verification of IMRT treatment delivery.« less
  • Purpose: Patient specific pre-treatment quality assurance (QA) using arrays of detectors or film have been the standard approach to assure the correct treatment is delivered to the patient. This QA approach is expensive, labor intensive and does not guarantee or document that all remaining fractions were treated properly. The purpose of this abstract is to commission and evaluate the performance of a commercially available in-vivo QA software using the electronic portal imaging device (EPID) to record the daily treatments. Methods: The platform EPIgray V2.0.2 (Dosisoft), which machine model compares ratios of TMR with EPID signal to predict dose was commissionedmore » for an Artiste (Siemens Oncology Care Systems) and a Truebeam (Varian medical systems) linear accelerator following the given instructions. The systems were then tested on three different phantoms (homogeneous stack of solid water, anthropomorphic head and pelvis) and on a library of patient cases. Simple and complex fields were delivered at different exposures and for different gantry angles. The effects of the table attenuation and the EPID sagging were evaluated. Gamma analysis of the measured dose was compared to the predicted dose for complex clinical IMRT cases. Results: Commissioning of the EPIgray system for two photon energies took 8 hours. The difference between the dose planned and the dose measured with EPIgray was better than 3% for all phantom scenarios tested. Preliminary results on patients demonstrate an accuracy of 5% is achievable in high dose regions for both 3DCRT and IMRT. Large discrepancies (>5%) were observed due to metallic structures or air cavities and in low dose areas. Flat panel sagging was visible and accounted for in the EPIgray model. Conclusion: The accuracy achieved by EPIgray is sufficient to document the safe delivery of complex IMRT treatments. Future work will evaluate EPIgray for VMAT and high dose rate deliveries. This work is supported by Dosisoft, Cachan, France.« less
  • Purpose: To evaluate the daily setup variation and the anatomic movement of the heart and lungs during breast irradiation with tangential photon beams, as measured with an electronic portal imaging device. Methods and materials: Analysis of 1,709 portal images determined changes in the radiation field during a treatment course in 8 patients. Values obtained for every image included central lung distance (CLD) and area of lung and heart within the irradiated field. The data from these measurements were used to evaluate variation from setup between treatment days and motion due to respiration and/or patient movement during treatment delivery. Results: Themore » effect of respiratory motion and movement during treatment was minimal: the maximum range in CLD for any patient on any day was 0.25 cm. The variation caused by day-to-day setup variation was greater, with CLD values for patients ranging from 0.59 cm to 2.94 cm. Similar findings were found for heart and lung areas. Conclusions: There is very little change in CLD and corresponding lung and heart area during individual radiation treatment fractions in breast tangential fields, compared with a relatively greater amount of variation that occurs between days.« less