J Grigsby

Washington University in St. Louis, San Luis, Missouri, United States

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Publications (3)5.61 Total impact

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    ABSTRACT: Tomotherapy is an image-guided, intensity-modulated radiation therapy system that delivers highly conformal dose distributions in a helical fashion. This system is also capable of acquiring megavoltage computed-tomography images and registering them to the planning kVCT images for accurate target localization. Quality assurance (QA) of this device is time intensive, but can be expedited by improved QA tools and procedures. A custom-designed phantom was fabricated to improve the efficiency of daily QA of our Tomotherapy machine. The phantom incorporates ionization chamber measurement points, plugs of different densities and slide-out film cartridges. The QA procedure was designed to verify in less than 30 min the vital components of the tomotherapy system: static beam quality and output, image quality, correctness of image registration and energy of the helical dose delivery. Machine output, percent depth dose and off-axis factors are simultaneously evaluated using a static 5 x 40 cm(2) open field. A single phantom scan is used to evaluate image quality and registration accuracy. The phantom can also be used for patient plan-specific QA. The QA results over a period of 6 months are reported in this paper. The QA process was found to be simple, efficient and capable of simultaneously verifying several important parameters.
    Physics in Medicine and Biology 10/2009; 54(19):5663-74. · 2.70 Impact Factor
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    ABSTRACT: Purpose: To verify the patient‐specific dosimetric accuracy of the helical tomotherapy system. Methods and Materials: Tomotherapy is a new and complex delivery system. Varying parameters such as pitch and modulating the beam at various angles during fan‐beam delivery can produce highly conformal dose distributions. Patient‐specific dosimetric verification is thus critical. This study uses a custom‐designed 18×18×18 cm3 phantom made from water‐equivalent plastic and Exradin A1SL ionization chambers to perform patient‐specific quality assurance (QA) procedures. During treatment, proper positioning of the patient is critical to avoid compromising treatment delivery. Tomotherapy allows roll correction to compensate for patient positioning errors. The roll correction was tested for 5°, 10°, 20°, and 30° using radiographic film dosimetry, the “cheese” phantom and the custom‐designed cuboid phantom. Results: Average ionization chamber correction factors for all patients treated on Tomotherapy were within 1.2%. Film dosimetry for every patient was also performed prior to treatment. Gamma and isodose overlay profiles were analyzed using commercial film analysis software. Results showed no significant dose delivery errors, and all patients passed within 5%. Gamma analysis was performed and showed excellent agreement by comparison with plans without phantom rotation.. Gamma values were within 3.3% at 3mm and 5% distance to agreement. A custom leaf‐control file, or sinogram, is created for each patient's plan, and replicated each time the patient plan is to be delivered. Dosimetric verification for three patient plans was performed to verify the integrity of the sinogram replication process. Results for each tested plan agreement within 1% for each patient fraction. Conclusion: Tomotherapy allows for accurate delivery, and accurately applies the roll correction as shown by direct dose distribution measurements. Conflict of Interest: This work supported in part by a grant from Tomotherapy, Inc.
    Medical Physics 05/2007; 34(6):2498-2499. · 2.91 Impact Factor
  • Medical Physics - MED PHYS. 01/2006; 33(6).