I am an assistant professor in the Department of Human Oncology. My clinical focus is on brachytherapy and imaging for radiation therapy, specifically CT simulation. CT imaging has made great advances, such as dual-energy CT, and I am passionate about understanding the ways in which these technologies can benefit our patients.
In addition to my clinical and research roles, I also enjoy the many teaching opportunities available at the University of Wisconsin. I teach a graduate-level brachytherapy course for the Department of Medical Physics. Within the Department of Human Oncology, I serve as a mentor for the medical physics residency program. I focus on training residents in the physics of different dosimeters and imaging techniques.
PhD, University of Wisconsin–Madison, Medical Physics (2013)
MS, University of Wisconsin–Madison, Medical Physics (2009)
BA/BS, University of Idaho and University of the Basque Country, Physics and Spanish (2007)
Assistant Professor, Human Oncology (2015–pres.)
Assistant Researcher, Human Oncology (2013–2015)
Research Assistant, Medical Physics (2007–2013)
Selected Honors and Awards
Editor’s pick for the Journal of Medical Physics (2016)
University of Wisconsin Ride Scholar (2016)
First Place, Young Investigator Competition at NCC of the AAPM Meeting (2013)
First Place, Young Investigator Competition at NCC of the AAPM Meeting (2009)
Student Travel Grant Award Winner, Annual Meeting of the CIRMS (2009)
Physics Student of the Year, University of Idaho (2007)
Leonard Halland Physics Scholarship (2007)
College of Science Dean’s List (2003–2007)
University of Idaho Honors Scholarship (2003–2007)
Idaho Academic Scholarship (2003–2007)
Boards, Advisory Committees and Professional Organizations
Accredited Dosimetry Calibration Laboratory Advisory Board Committee Member (2017–pres.)
CT Simulation Improvement Committee Chair (2017-pres.)
Medical Physics Residency Advisory Committee Member (2017–pres.)
Doctoral Candidate Research Advisor (2017–pres.)
Doctoral Candidate Committee Member (2016–pres.)
Radiation Oncology Residency Program Selection Committee Member (2016–pres.)
Medical Physics Residency Program Selection Committee Member (2016–pres.)
Medical Physics Residency Program Curriculum Committee Member (2016–pres.)
UW–La Crosse Medical Dosimetry Program Selection Committee (2014–2015)
UWMRRC Research Oversight Committee (2010–2013)
American Association of Physicists in Medicine (2008–pres.)
Council of Ionization Radiation Measurements (2008–2013)
Brachytherapy, Clinical Operations, Imaging, Motion Management, Radiation Measurements
Research is a critical component to implementing new technologies that allow us to improve care for our patients in the fight against cancer.
Radiation therapy relies on an accurate understanding of tumor location within a patient as well as an accurate model of the radiation beam to be delivered. My research focuses on both of these aspects of radiation therapy delivery. Through optimized CT imaging we can better define the boundaries of a tumor and target the cancer more effectively. I also work with radiation detectors to characterize their response to radiation for a more accurate measurement of dose.
Improving tumor delineation in the pancreas and liver through dual-energy CT
Tumor delineation in the pancreas and liver can be a challenge using conventional CT images. Dual-Energy CT provides many opportunities to better delineate tumor from healthy tissue and therefore has great potential to aid in radiation therapy. The Department of Human Oncology has installed a novel single-source dual-energy CT system, called TwinBeam, with potential for liver and pancreas imaging. We are currently quantifying the advantages gained through TwinBeam dual-energy CT.
Polarity and ion recombination effects in Microionization chambers
An increase in the delivery of small and nonstandard radiation fields has led to the development of small-volume ionization chambers, commonly categorized as microchambers. Small-volume dosimeters can provide high spatial resolution in areas of steep dose gradients. The University of Wisconsin Accredited Dosimetry Calibration Laboratory has experienced an increase in requests for the calibration of microchambers. This indicates that these chambers are being used for reference dosimetry measurements in a wide range of therapy applications. Unfortunately, microchambers exhibit anomalous polarity and ion recombination effects that are not demonstrated by larger-volume, reference-class ionization chambers. We are working to better understand and characterize these chambers.
Investigating a novel split-filter dual-energy CT technique for improving pancreas tumor visibility for radiation therapy. J Appl Clin Med Phys
Di Maso LD, Huang J, Bassetti MF, DeWerd LA, Miller JR
2018 Aug 17; :
PURPOSE: Tumor delineation using conventional CT images can be a challenge for pancreatic adenocarcinoma where contrast between the tumor and surrounding healthy tissue is low. This work investigates the ability of a split-filter dual-energy CT (DECT) system to improve pancreatic tumor contrast and contrast-to-noise ratio (CNR) for radiation therapy treatment planning.
MATERIALS AND METHODS: Multiphasic scans of 20 pancreatic tumors were acquired using a split-filter DECT technique with iodinated contrast medium, OMNIPAQUETM . Analysis was performed on the pancreatic and portal venous phases for several types of DECT images. Pancreatic gross target volume (GTV) contrast and CNR were calculated and analyzed from mixed 120 kVp-equivalent images and virtual monoenergetic images (VMI) at 57 and 40 keV. The role of iterative reconstruction on DECT images was also investigated. Paired t-tests were used to assess the difference in GTV contrast and CNR among the different images.
RESULTS: The VMIs at 40 keV had a 110% greater image noise compared to the mixed 120 kVp-equivalent images (P < 0.0001). VMIs at 40 keV increased GTV contrast from 15.9 ± 19.9 HU to 93.7 ± 49.6 HU and CNR from 1.37 ± 2.05 to 3.86 ± 2.78 in comparison to the mixed 120 kVp-equivalent images. The iterative reconstruction algorithm investigated decreased noise in the VMIs by about 20% and improved CNR by about 30%.
CONCLUSIONS: Pancreatic tumor contrast and CNR were significantly improved using VMIs reconstructed from the split-filter DECT technique, and the use of iterative reconstruction further improved CNR. This gain in tumor contrast may lead to more accurate tumor delineation for radiation therapy treatment planning.View details for PubMedID 30117641
Novel use of ViewRay MRI guidance for high-dose-rate brachytherapy in the treatment of cervical cancer. Brachytherapy
Ko HC, Huang JY, Miller JR, Das RK, Wallace CR, De Costa AA, Francis DM, Straub MR, Anderson BM, Bradley KA
2018 May 14; :
Reply to: Comment on: polarity effects and apparent ion recombination in microionization chambers [Med. Phys. 43(5) 2141-2152 (2016)]. Med Phys
Miller JR, Hooten BD, Micka JA, DeWerd LA
2017 Mar; 44 (3): 1206-1207
We would like to thank Dr. Brivio et al. [Med. Phys.] for their comment on our recent paper. Miller et al. [Med. Phys. 43 (2016) 2141-2152] determined the primary cause of voltage-dependent polarity effects in microchambers to be a potential difference between the guard and collecting electrodes. In their comment, Brivio et al., offer an explanation for the cause of such potential differences. Brivio et al. attribute the potential difference to the disparity in the work functions between guard and collecting electrodes composed of different materials. However, all of the microchambers investigated in Miller et al. contained a guard and collecting electrode which were composed of the same material. Therefore, the explanation offered by Brivio et al. that "the electric potential perturbation arises from the work function difference of the disparate materials electrodes" does not explain the polarity effects exhibited by the microchambers investigated in Miller et al., all of which contain electrodes composed of the same materials.View details for PubMedID 28052335
Ion recombination and polarity corrections for small-volume ionization chambers in high-dose-rate, flattening-filter-free pulsed photon beams. Med Phys
Hyun MA, Miller JR, Micka JA, DeWerd LA
2017 Feb; 44 (2): 618-627
PURPOSE: To investigate ion recombination and polarity effects in scanning and microionization chambers when used with digital electrometers and high-dose-rate linac beams such as flattening-filter-free (FFF) fields, and to compare results against conventional pulsed and continuous photon beams.
METHODS: Saturation curves were obtained for one Farmer-type ionization chamber and eight small-volume chamber models with volumes ranging from 0.01 to 0.13 cm(3) using a Varian TrueBeam™ STx with FFF capability. Three beam modes (6 MV, 6 MV FFF, and 10 MV FFF) were investigated, with nominal dose-per-pulse values of 0.0278, 0.0648, and 0.111 cGy/pulse, respectively, at dmax . Saturation curves obtained using the Theratronics T1000 (60) Co unit at the UWADCL and a conventional linear accelerator (Varian Clinac iX) were used to establish baseline behavior. Jaffé plots were fitted to obtain Pion , accounting for exponential effects such as charge multiplication. These values were compared with the two-voltage technique recommended in TG-51, and were plotted as a function of dose-per-pulse to assess the ability of small-volume chambers to meet reference-class criteria in FFF beams.
RESULTS: Jaffé- and two-voltage-determined Pion values measured for high-dose-rate beams agreed within 0.1% for the Farmer-type chamber and 1% for scanning and microionization chambers, with the exception of the CC01 which agreed within 2%. With respect to ion recombination and polarity effects, the Farmer-type chamber, scanning chambers and the Exradin A26 microchamber exhibited reference-class behavior in all beams investigated, with the exception of the IBA CC04 scanning chamber, which had an initial recombination correction that varied by 0.2% with polarity. All microchambers investigated, with the exception of the A26, exhibited anomalous polarity and ion recombination behaviors that make them unsuitable for reference dosimetry in conventional and high-dose-rate photon beams.
CONCLUSIONS: The results of this work demonstrate that recombination and polarity behaviors seen in conventional pulsed and continuous photon beams trend accordingly in high-dose-rate FFF linac beams. Several models of small-volume ionization chambers used with a digital electrometer have been shown to meet reference-class requirements with respect to ion recombination and polarity, even in the high-dose-rate environment. For such chambers, a two-voltage technique agreed well with more rigorous methods of determining Pion . However, the results emphasize the need for careful reference detector selection, and indicate that ionization chambers ought to be extensively tested in each beam of interest prior to their use for reference dosimetry.View details for PubMedID 28001291
Polarity effects and apparent ion recombination in microionization chambers. Med Phys
Miller JR, Hooten BD, Micka JA, DeWerd LA
2016 May; 43 (5): 2141
PURPOSE: Microchambers demonstrate anomalous voltage-dependent polarity effects. Existing polarity and ion recombination correction factors do not account for these effects. As a result, many commercial microchamber models do not meet the specification of a reference-class ionization chamber as defined by the American Association of Physicists in Medicine. The purpose of this investigation is to determine the cause of these voltage-dependent polarity effects.
METHODS: A series of microchamber prototypes were produced to isolate the source of the voltage-dependent polarity effects. Parameters including ionization-chamber collecting-volume size, stem and cable irradiation, chamber assembly, contaminants, high-Z materials, and individual chamber components were investigated. Measurements were performed with electrodes coated with graphite to isolate electrode conductivity. Chamber response was measured as the potential bias of the guard electrode was altered with respect to the collecting electrode, through the integration of additional power supplies. Ionization chamber models were also simulated using comsol Multiphysics software to investigate the effect of a potential difference between electrodes on electric field lines and collecting volume definition.
RESULTS: Investigations with microchamber prototypes demonstrated that the significant source of the voltage-dependent polarity effects was a potential difference between the guard and collecting electrodes of the chambers. The voltage-dependent polarity effects for each prototype were primarily isolated to either the guard or collecting electrode. Polarity effects were reduced by coating the isolated electrode with a conductive layer of graphite. Polarity effects were increased by introducing a potential difference between the electrodes. comsol simulations further demonstrated that for a given potential difference between electrodes, the collecting volume of the chamber changed as the applied voltage was altered, producing voltage-dependent polarity effects in the chamber response. Ionization chamber measurements and comsol simulations demonstrated an inverse relationship between the chamber collecting volume size and the severity of voltage-dependent polarity effects on chamber response. The effect of a given potential difference on chamber polarity effects was roughly ten times greater for microchambers as compared to Farmer-type chambers. Stem and cable irradiations, chamber assembly, contaminants, and high-Z materials were not found to be a significant source of the voltage-dependent polarity effects.
CONCLUSIONS: A potential difference between the guard and collecting electrodes was found to be the primary source of the voltage-dependent polarity effects demonstrated by microchambers. For a given potential difference between electrodes, the relative change in the collecting volume is smaller for larger-volume chambers, illustrating why these polarity effects are not seen in larger-volume chambers with similar guard and collecting electrode designs. Thus, for small-volume chambers, it is necessary to reduce the potential difference between the guard and collecting electrodes in order to reduce polarity effects for reference dosimetry measurements.View details for PubMedID 27147326
Jessica Miller, PhD600 Highland Avenue,
Madison, WI 53792