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Title: TomoTherapy MLC verification using exit detector data

Abstract

Purpose: Treatment delivery verification (DV) is important in the field of intensity modulated radiation therapy (IMRT). While IMRT and image guided radiation therapy (IGRT), allow us to create more conformal plans and enables the use of tighter margins, an erroneously executed plan can have detrimental effects on the treatment outcome. The purpose of this study is to develop a DV technique to verify TomoTherapy's multileaf collimator (MLC) using the onboard mega-voltage CT detectors. Methods: The proposed DV method uses temporal changes in the MVCT detector signal to predict actual leaf open times delivered on the treatment machine. Penumbra and scattered radiation effects may produce confounding results when determining leaf open times from the raw detector data. To reduce the impact of the effects, an iterative, Richardson-Lucy (R-L) deconvolution algorithm is applied. Optical sensors installed on each MLC leaf are used to verify the accuracy of the DV technique. The robustness of the DV technique is examined by introducing different attenuation materials in the beam. Additionally, the DV technique has been used to investigate several clinical plans which failed to pass delivery quality assurance (DQA) and was successful in identifying MLC timing discrepancies as the root cause. Results: The leaf openmore » time extracted from the exit detector showed good agreement with the optical sensors under a variety of conditions. Detector-measured leaf open times agreed with optical sensor data to within 0.2 ms, and 99% of the results agreed within 8.5 ms. These results changed little when attenuation was added in the beam. For the clinical plans failing DQA, the dose calculated from reconstructed leaf open times played an instrumental role in discovering the root-cause of the problem. Throughout the retrospective study, it is found that the reconstructed dose always agrees with measured doses to within 1%. Conclusions: The exit detectors in the TomoTherapy treatment systems can provide valuable information about MLC behavior during delivery. A technique to estimate the TomoTherapy binary MLC leaf open time from exit detector signals is described. This technique is shown to be both robust and accurate for delivery verification.« less

Authors:
; ; ; ;  [1]
  1. TomoTherapy Inc., 1240 Deming Way, Madison, Wisconsin 53717 (United States)
Publication Date:
OSTI Identifier:
22100623
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 39; Journal Issue: 1; Other Information: (c) 2012 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; 60 APPLIED LIFE SCIENCES; ACCURACY; ALGORITHMS; ATTENUATION; BEAMS; BIOLOGICAL RADIATION EFFECTS; COLLIMATORS; COMPUTERIZED TOMOGRAPHY; CT-GUIDED RADIOTHERAPY; DELIVERY; DOSIMETRY; IMAGES; ITERATIVE METHODS; QUALITY ASSURANCE; RADIATION DETECTION; RADIATION DOSES; SENSORS

Citation Formats

Quan, Chen, Westerly, David, Zhenyu, Fang, Sheng, Ke, Yu, Chen, Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado 80045, Xinghua Cancer Hospital, Xinghua, Jiangsu 225700, Department of Radiation Oncology, University of California-Los Angeles, Los Angeles, California 90095, and TomoTherapy Inc., 1240 Deming Way, Madison, Wisconsin 53717. TomoTherapy MLC verification using exit detector data. United States: N. p., 2012. Web. doi:10.1118/1.3666762.
Quan, Chen, Westerly, David, Zhenyu, Fang, Sheng, Ke, Yu, Chen, Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado 80045, Xinghua Cancer Hospital, Xinghua, Jiangsu 225700, Department of Radiation Oncology, University of California-Los Angeles, Los Angeles, California 90095, & TomoTherapy Inc., 1240 Deming Way, Madison, Wisconsin 53717. TomoTherapy MLC verification using exit detector data. United States. https://doi.org/10.1118/1.3666762
Quan, Chen, Westerly, David, Zhenyu, Fang, Sheng, Ke, Yu, Chen, Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado 80045, Xinghua Cancer Hospital, Xinghua, Jiangsu 225700, Department of Radiation Oncology, University of California-Los Angeles, Los Angeles, California 90095, and TomoTherapy Inc., 1240 Deming Way, Madison, Wisconsin 53717. Sun . "TomoTherapy MLC verification using exit detector data". United States. https://doi.org/10.1118/1.3666762.
@article{osti_22100623,
title = {TomoTherapy MLC verification using exit detector data},
author = {Quan, Chen and Westerly, David and Zhenyu, Fang and Sheng, Ke and Yu, Chen and Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado 80045 and Xinghua Cancer Hospital, Xinghua, Jiangsu 225700 and Department of Radiation Oncology, University of California-Los Angeles, Los Angeles, California 90095 and TomoTherapy Inc., 1240 Deming Way, Madison, Wisconsin 53717},
abstractNote = {Purpose: Treatment delivery verification (DV) is important in the field of intensity modulated radiation therapy (IMRT). While IMRT and image guided radiation therapy (IGRT), allow us to create more conformal plans and enables the use of tighter margins, an erroneously executed plan can have detrimental effects on the treatment outcome. The purpose of this study is to develop a DV technique to verify TomoTherapy's multileaf collimator (MLC) using the onboard mega-voltage CT detectors. Methods: The proposed DV method uses temporal changes in the MVCT detector signal to predict actual leaf open times delivered on the treatment machine. Penumbra and scattered radiation effects may produce confounding results when determining leaf open times from the raw detector data. To reduce the impact of the effects, an iterative, Richardson-Lucy (R-L) deconvolution algorithm is applied. Optical sensors installed on each MLC leaf are used to verify the accuracy of the DV technique. The robustness of the DV technique is examined by introducing different attenuation materials in the beam. Additionally, the DV technique has been used to investigate several clinical plans which failed to pass delivery quality assurance (DQA) and was successful in identifying MLC timing discrepancies as the root cause. Results: The leaf open time extracted from the exit detector showed good agreement with the optical sensors under a variety of conditions. Detector-measured leaf open times agreed with optical sensor data to within 0.2 ms, and 99% of the results agreed within 8.5 ms. These results changed little when attenuation was added in the beam. For the clinical plans failing DQA, the dose calculated from reconstructed leaf open times played an instrumental role in discovering the root-cause of the problem. Throughout the retrospective study, it is found that the reconstructed dose always agrees with measured doses to within 1%. Conclusions: The exit detectors in the TomoTherapy treatment systems can provide valuable information about MLC behavior during delivery. A technique to estimate the TomoTherapy binary MLC leaf open time from exit detector signals is described. This technique is shown to be both robust and accurate for delivery verification.},
doi = {10.1118/1.3666762},
url = {https://www.osti.gov/biblio/22100623}, journal = {Medical Physics},
issn = {0094-2405},
number = 1,
volume = 39,
place = {United States},
year = {2012},
month = {1}
}