PhD, University of Wisconsin, Medical Physics (2022)
MS, University of Wisconsin, Medical Physics (2018)
BS, Mercyhurst University, Physics (2016)
Selected Honors and Awards
World Congress of Brachytherapy: Best Poster (2021)
CIRMS Junior Investigator Award (2020)
North Central Chapter AAPM MedPhys Slam! Finalist (2019)
Boards, Advisory Committees and Professional Organizations
American Association of Physicists in Medicine (AAPM) November 2018 -Present
North Central Chapter of American Association of Physicists in Medicine (AAPM) Student member November 2018 - 2022
Council on Ionizing Radiation Measurements and Standards Treasurer, May 2021 – present; Student representative, May 2018- May 2021
UW Medical Physics Graduate Student Representative May 2018-May 2020
What are your Clinical & Research Interests?
I really love all things clinical, but I’m excited to learn more about brachytherapy and SRS!
Why did you choose to come to UW
There were so many different opportunities to learn and expand my knowledge as a clinical medical physicist with the various special procedures we have here. Also, the entire department was so welcoming, and I really could see myself thriving as a trainee here.
Favorite part of residency, favorite rotation, or favorite thing about the program?
My favorite rotation (so far) has been the basic treatment planning rotation. I’ve also enjoyed working with different physicists on a number of clinical projects.
Favorite thing to do in Madison?
I love trying new food at all the different restaurants around and exploring all the state parks in the surrounding areas!
Fun fact about yourself or things you like to do for fun?
In my free time I enjoy baking, doing arts and crafts, and getting lots of snuggles from my two cats!
Biological Characterization of the Effects of Filtration on the Xoft Axxent® Electronic Brachytherapy Source for Cervical Cancer Applications Radiation research
Walter AE, Cosper PF, Nickel KP, Ramesh S, Khan AU, DeWerd LA, Kimple RJ
2023 May 1;199(5):429-438. doi: 10.1667/RADE-22-00112.1.
Low-energy X-ray sources that operate in the kilovoltage energy range have been shown to induce more cellular damage when compared to their megavoltage counterparts. However, low-energy X-ray sources are more susceptible to the effects of filtration on the beam spectrum. This work sought to characterize the biological effects of the Xoft Axxent® source, a low-energy therapeutic X-ray source, both with and without the titanium vaginal applicator in place. It was hypothesized that there would be an increase in relative biological effectiveness (RBE) of the Axxent® source compared to 60Co and that the source in the titanium vaginal applicator (SIA) would have decreased biological effects compared to the bare source (BS). This hypothesis was drawn from linear energy transfer (LET) simulations performed using the TOPAS Monte Carlo user code as well a reduction in dose rate of the SIA compared to the BS. A HeLa cell line was maintained and used to evaluate these effects. Clonogenic survival assays were performed to evaluate differences in the RBE between the BS and SIA using 60Co as the reference beam quality. Neutral comet assay was used to assess induction of DNA strand damage by each beam to estimate differences in RBE. Quantification of mitotic errors was used to evaluate differences in chromosomal instability (CIN) induced by the three beam qualities. The BS was responsible for the greatest quantity of cell death due to a greater number of DNA double strand breaks (DSB) and CIN observed in the cells. The differences observed in the BS and SIA surviving fractions and RBE values were consistent with the 13% difference in LET as well as the factor of 3.5 reduction in dose rate of the SIA. Results from the comet and CIN assays were consistent with these results as well. The use of the titanium applicator results in a reduction in the biological effects observed with these sources, but still provides an advantage over megavoltage beam qualities. © 2023 by Radiation Research Society.
PMID:37014873 | PMC:PMC10288372 | DOI:10.1667/RADE-22-00112.1
View details for PubMedID 37014873
Determination of an air kerma-rate correction factor for the S7600 Xoft Axxent<sup>Ⓡ</sup> source model Brachytherapy
Walter AE, DeWerd LA
2023 Jul-Aug;22(4):512-517. doi: 10.1016/j.brachy.2023.02.005. Epub 2023 Mar 23.
PURPOSE: The purpose of this work was to provide guidance for the lack of an air-kerma rate standard for the S7600 Xoft Axxent® source by providing a correction factor to apply to the National Institute of Standards and Technology (NIST) traceable S7500 well chamber (WC) calibration coefficient before the development of an S7600 standard at NIST.
METHODS AND MATERIALS: The Attix free air chamber (FAC) at the University of Wisconsin Medical Radiation Research Center was used to measure the air-kerma rate at 50 cm for six S7500 and six S7600 sources. These same sources were then measured using five standard imaging HDR1000+ WCs. The measurements made with the FAC were used to calculate source-specific WC calibration coefficients for the S7500 and S7600 source. These results were compared to the NIST traceable calibration coefficients for the S7500 source. The average results for each WC were then averaged together, and a ratio of the S7600 to S7500 WC calibration coefficients was determined.
RESULTS: The average S7600 air-kerma rate measurement with the FAC was 7% lower than the average air-kerma rate measurements of the S7500 source. On average, the S7500 determined WC calibration coefficients agreed within ±1% of the NIST traceable S7500 values. The S7600 WC calibration coefficients were up to 16% less than the NIST traceable S7500 values. The final correction factor determined to be applied to the NIST traceable S7500 value was 0.8415 with an associated uncertainty of ±8.1% at k = 2.
CONCLUSIONS: This work provides a suggested correction factor for the S7600 Xoft Axxent source such that the sources can be accurately implemented in the clinical setting.
PMID:36966035 | DOI:10.1016/j.brachy.2023.02.005
View details for PubMedID 36966035
Measurement of the modified TG43 parameters for the bare S7600 Xoft Axxent source model Brachytherapy
Walter AE, Khan AU, DeWerd LA
2023 Mar-Apr;22(2):260-268. doi: 10.1016/j.brachy.2022.11.010. Epub 2023 Jan 7.
PURPOSE: The purpose of this work is to provide measured data for the modified TG43 parameters [DeWerd et al.] for the newest, Galden-cooled S7600 Xoft Axxent source model.
METHODS: The measurement of radial dose distributions at distances of 1 cm to 4 cm from the source was performed using TLD100 microcubes, EBT3 film, and an Exradin A26 microionization chamber. The overall uncertainty and reproducibility of each dosimeter was evaluated for its use in determining the radial dose function and dose rate conversion coefficient. An acrylic phantom developed in house for previous works was used to measure the polar anisotropy function using TLD100 microcubes at distances of 1 cm, 2 cm, and 5 cm from the source.
RESULTS: The Exradin A26 chamber was deemed most suitable for measuring the radial dose function. Values determined had a maximum k = 1 uncertainty of 1.4%. The dose rate conversion coefficient measured with the chamber was found to be 9.33 ± 0.21cGy/hrμGy/min. TLD100 microcube measurements of the polar anisotropy had average uncertainties of 6%, 3%, and 2.5% at 1 cm, 2 cm, and 5 cm, respectively.
CONCLUSIONS: The modified TG43 parameters for the bare source were measured with reasonable uncertainty. The values determined will aid with the clinical implementation of the source for breast and endometrial cancer applications.
PMID:36623989 | DOI:10.1016/j.brachy.2022.11.010
View details for PubMedID 36623989
Comparison of air kerma rate between the S7500 and S7600 xoft axxent sources Brachytherapy
Walter AE, Hull JL, DeWerd LA
2022 May-Jun;21(3):354-361. doi: 10.1016/j.brachy.2021.12.005. Epub 2022 Feb 3.
PURPOSE: The purpose of this work was to evaluate differences in air-kerma rate of the older, S7500 water-cooled Xoft Axxent source and newer, S7600 Galden-cooled source.
METHODS AND MATERIALS: The Attix Free Air Chamber (FAC) at the UWMRRC was used to measure the air-kerma rate at 50 cm for six S7600 Xoft Axxent sources. The average measured air-kerma of the S7600 sources was compared with the measured average air-kerma rate from five S7500 sources. The air-kerma rates of the S7500 sources were measured in a Standard Imaging HDR 1000+ well chamber. The FAC measurements were used to determine a well chamber calibration coefficient for the S7600 source. The S7500 calibration coefficients were incorrectly applied to the S7600 sources to indicate the magnitude of error that can occur if the incorrect calibration coefficient is used.
RESULTS: A 10.3% difference was observed between the average air-kerma rates of the two sources although a 17% difference was observed between their calibration coefficients. The application of the S7500 calibration coefficient to the S7600 sources resulted in measured air-kerma rates that were 20% greater than the true value.
CONCLUSIONS: This work indicates the need for a new air-kerma rate standard for the S7600 sources, and the results presented in this work are indicative of values that would be obtained at National Institute of Standards and Technology.
PMID:35123888 | DOI:10.1016/j.brachy.2021.12.005
View details for PubMedID 35123888
Evaluation of ionization chamber stability checks using various sources Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)
Walter AE, Hansen JB, DeWerd LA
2020 Dec;80:327-334. doi: 10.1016/j.ejmp.2020.11.010. Epub 2020 Nov 26.
PURPOSE: It is important to check stability of ionization chambers in between regular calibration cycles. Stability checks can include individual 60Co irradiations, use of a beta-emitting check source, or redundant measurements in megavoltage photon beams. While 60Co irradiators are considered stable, they are rarely found in the clinical setting. Thus, this study seeks to compare the precision and efficiency in monitoring chamber stability using 90Sr check sources and linear accelerator beams which are both commonly found in the clinical setting, and compare these sources to 60Co.
METHODS: Measurements were made with a 90Sr beta-emitting check source and a 6 MV photon beam using a Constancy Check Phantom with three custom inserts to hold the ionization chambers. A comparison of both methods was performed with an Exradin A28 scanning chamber, Wellhofer IC69 Farmer-type chamber, and Exradin A12 Farmer-type chamber. Chamber stability was evaluated with individual charge readings and charge ratios among the three chambers. Results were compared to measurements taken in 60Co with three Farmer-type chambers: the NEL 2571, PTW N30001G, and Exradin A12.
RESULTS: Stability of individual charge reading was found to be within ±1.0% for 90Sr source measurements and ±0.5% for external beam measurements, including the 60Co comparison. Additionally, the standard deviation of the mean charge ratios ranged from 0.15% to 0.40% for 90Sr measurements and from 0.10% to 0.30% for the external beam measurements.
CONCLUSIONS: This work provides a comparison of techniques used to assess stability of ionization chambers in order to better inform the clinical physicist.
PMID:33249393 | DOI:10.1016/j.ejmp.2020.11.010
View details for PubMedID 33249393