I am an assistant professor in the Department of Human Oncology, providing primarily clinical support, but also serving in research and teaching roles. I support our TrueBeam radiotherapy program, performing routine quality assurance and overseeing the respiratory motion management program. Additionally, I serve on departmental committees for the improvement of our CT simulation and TrueBeam treatment processes.
As a mentor in our medical physics residency program, I teach operation and quality assurance of linear accelerators to medical physics residents.
My research interests include motion management, MR-guided radiation therapy, and management of uncertainties in radiation therapy, in particular the use of surface monitoring, fiducial tracking, and MR imaging to better quantify and reduce necessary treatment margins.
Resident, University of Pittsburgh Medical Center, Medical Physics (2017)
PhD, University of Wisconsin–Madison, Medical Physics (2015)
MS, University of Wisconsin–Madison, Medical Physics (2011)
BS, North Carolina State University, Physics (2009)
BS, North Carolina State University, Applied Mathematics (2009)
Assistant Professor, Human Oncology (2017)
Selected Honors and Awards
Penn-Ohio Chapter of the American Association of Physicists in Medicine (AAPM) Travel Grant (2016)
Vilas Conference Presentation Funding Award, University of Wisconsin (2013)
Medical Physics Biological Sciences Fellowship, University of Wisconsin (2009)
Boards, Advisory Committees and Professional Organizations
Chair, TrueBeam Service Improvement Committee (2018-pres.)
Member, University of Wisconsin Accredited Dosimetry Calibration Laboratory Advisory Committee (2017–pres.)
Member, Computed Tomography Simulation Improvement Committee (2017-pres.)
Reviewer, Medical Physics, Journal of Applied Clinical Medical Physics, and Radiation Measurements journals (2011-pres.)
Member, American Association of Physicists in Medicine (2010-pres.)
Motion Management, MR-Guided Radiation Therapy, Uncertainties in Radiation Therapy, Radiation Measurements
Diagnosing atmospheric communication of a sealed monitor chamber. J Appl Clin Med Phys
McCaw TJ, Barraclough BA, Belanger M, Besemer A, Dunkerley DAP, Labby ZE
2020 Jul 10; :
Daily output variations of up to ±2% were observed for a protracted time on a Varian TrueBeam® STx; these output variations were hypothesized to be the result of atmospheric communication of the sealed monitor chamber. Daily changes in output relative to baseline, measured with an ionization chamber array (DQA3) and the amorphous silicon flat panel detector (IDU) on the TrueBeam®, were compared with daily temperature-pressure corrections (PTP ) determined from sensors within the DQA3. Output measurements were performed using a Farmer® ionization chamber over a 5-hour period, during which there was controlled variation in the monitor chamber temperature. The root mean square difference between percentage output change from baseline measured with the DQA3 and IDU was 0.50% over all measurements. Over a 7-month retrospective review of daily changes in output and PTP , weak correlation (R2 = 0.30) was observed between output and PTP for the first 5 months; for the final 2 months, daily output changes were linearly correlated with changes in PTP , with a slope of 0.84 (R2 = 0.89). Ionization measurements corrected for ambient temperature and pressure during controlled heating and cooling of the monitor chamber differed from expected values for a sealed monitor chamber by up to 4.6%, but were consistent with expectation for an air-communicating monitor chamber within uncertainty (1.3%, k = 2). Following replacement of the depressurized monitor chamber, there has been no correlation between daily percentage change in output and PTP (R2 = 0.09). The utility of control charts is demonstrated for earlier identification of changes in the sensitivity of a sealed monitor chamber.View details for PubMedID 32648368
Comparison of the recommendations of the AAPM TG-51 and TG-51 addendum reference dosimetry protocols. J Appl Clin Med Phys
McCaw TJ, Hwang MS, Jang SY, Huq MS
2017 Jul; 18 (4): 140-143
This work quantified differences between recommendations of the TG-51 and TG-51 addendum reference dosimetry protocols. Reference dosimetry was performed for flattened photon beams with nominal energies of 6, 10, 15, and 23 MV, as well as flattening-filter free (FFF) beam energies of 6 and 10 MV, following the recommendations of both the TG-51 and TG-51 addendum protocols using both a Farmer® ionization chamber and a scanning ionization chamber with calibration coefficients traceable to absorbed dose-to-water (Dw ) standards. Differences in Dw determined by the two protocols were 0.1%-0.3% for beam energies with a flattening filter, and up to 0.2% and 0.8% for FFF beams measured with the scanning and Farmer® ionization chambers, respectively, due to kQ determination, volume-averaging correction, and collimator jaw setting. Combined uncertainty was between 0.91% and 1.2% (k = 1), varying by protocol and detector.View details for PubMedID 28574211
Development and characterization of a three-dimensional radiochromic film stack dosimeter for megavoltage photon beam dosimetry. Med Phys
McCaw TJ, Micka JA, DeWerd LA
2014 May; 41 (5): 052104
PURPOSE: Three-dimensional (3D) dosimeters are particularly useful for verifying the commissioning of treatment planning and delivery systems, especially with the ever-increasing implementation of complex and conformal radiotherapy techniques such as volumetric modulated arc therapy. However, currently available 3D dosimeters require extensive experience to prepare and analyze, and are subject to large measurement uncertainties. This work aims to provide a more readily implementable 3D dosimeter with the development and characterization of a radiochromic film stack dosimeter for megavoltage photon beam dosimetry.
METHODS: A film stack dosimeter was developed using Gafchromic(®) EBT2 films. The dosimeter consists of 22 films separated by 1 mm-thick spacers. A Virtual Water™ phantom was created that maintains the radial film alignment within a maximum uncertainty of 0.3 mm. The film stack dosimeter was characterized using simulations and measurements of 6 MV fields. The absorbed-dose energy dependence and orientation dependence of the film stack dosimeter were investigated using Monte Carlo simulations. The water equivalence of the dosimeter was determined by comparing percentage-depth-dose (PDD) profiles measured with the film stack dosimeter and simulated using Monte Carlo methods. Film stack dosimeter measurements were verified with thermoluminescent dosimeter (TLD) microcube measurements. The film stack dosimeter was also used to verify the delivery of an intensity-modulated radiation therapy (IMRT) procedure.
RESULTS: The absorbed-dose energy response of EBT2 film differs less than 1.5% between the calibration and film stack dosimeter geometries for a 6 MV spectrum. Over a series of beam angles ranging from normal incidence to parallel incidence, the overall variation in the response of the film stack dosimeter is within a range of 2.5%. Relative to the response to a normally incident beam, the film stack dosimeter exhibits a 1% under-response when the beam axis is parallel to the film planes. Measured and simulated PDD profiles agree within a root-mean-square difference of 1.3%. In-field film stack dosimeter and TLD measurements agree within 5%, and measurements in the field penumbra agree within 0.5 mm. Film stack dosimeter and TLD measurements have expanded (k = 2) overall measurement uncertainties of 6.2% and 5.8%, respectively. Film stack dosimeter measurements of an IMRT dose distribution have 98% agreement with the treatment planning system dose calculation, using gamma criteria of 3% and 2 mm.
CONCLUSIONS: The film stack dosimeter is capable of high-resolution, low-uncertainty 3D dose measurements, and can be readily incorporated into an existing film dosimetry program.View details for PubMedID 24784393
Characterizing the marker-dye correction for Gafchromic(®) EBT2 film: a comparison of three analysis methods. Med Phys
McCaw TJ, Micka JA, Dewerd LA
2011 Oct; 38 (10): 5771-7
PURPOSE: Gafchromic(®) EBT2 film has a yellow marker dye incorporated into the active layer of the film that can be used to correct the film response for small variations in thickness. This work characterizes the effect of the marker-dye correction on the uniformity and uncertainty of dose measurements with EBT2 film. The effect of variations in time postexposure on the uniformity of EBT2 is also investigated.
METHODS: EBT2 films were used to measure the flatness of a (60)Co field to provide a high-spatial resolution evaluation of the film uniformity. As a reference, the flatness of the (60)Co field was also measured with Kodak EDR2 films. The EBT2 films were digitized with a flatbed document scanner 24, 48, and 72 h postexposure, and the images were analyzed using three methods: (1) the manufacturer-recommended marker-dye correction, (2) an in-house marker-dye correction, and (3) a net optical density (OD) measurement in the red color channel. The field flatness was calculated from orthogonal profiles through the center of the field using each analysis method, and the results were compared with the EDR2 measurements. Uncertainty was propagated through a dose calculation for each analysis method. The change in the measured field flatness for increasing times postexposure was also determined.
RESULTS: Both marker-dye correction methods improved the field flatness measured with EBT2 film relative to the net OD method, with a maximum improvement of 1% using the manufacturer-recommended correction. However, the manufacturer-recommended correction also resulted in a dose uncertainty an order of magnitude greater than the other two methods. The in-house marker-dye correction lowered the dose uncertainty relative to the net OD method. The measured field flatness did not exhibit any unidirectional change with increasing time postexposure and showed a maximum change of 0.3%.
CONCLUSIONS: The marker dye in EBT2 can be used to improve the response uniformity of the film. Depending on the film analysis method used, however, application of a marker-dye correction can improve or degrade the dose uncertainty relative to the net OD method. The uniformity of EBT2 was found to be independent of the time postexposure.View details for PubMedID 21992391
Travis McCaw, PhD600 Highland Avenue,
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