Patrick Hill, PhD

Patrick Hill, PhD

Assistant Professor (CHS)

Department of Human Oncology

I am an assistant professor in the Department of Human Oncology. My primary role is to provide clinical medical physics services in the Department of Radiation Oncology at the UW Health University Hospital. In the clinic, I perform tasks to ensure that patients are being treated safely and accurately on each day of their treatment. This includes making sure radiation-producing machines are operating correctly and that the quality of a patient’s treatment is maintained from the day they first arrive in our department to the day of their last treatment. I am among the primary physics contacts for our TomoTherapy systems, radiosurgery program, total-body and total-skin irradiation programs, treatment planning systems and image processing software.

The radiotherapy process requires a diverse team of physicians, physicists, dosimetrists, therapists, nurses and others. Much of my efforts are focused on improving the ways in which this team can come together and care for patients. I have detailed knowledge of clinical operations along with the hardware and software tools we use on a daily basis. I do things like develop processes to better achieve treatment goals, learn and implement new technology and design and execute quality assurance tests that ensure our equipment is functioning properly.

Outside the clinic, I teach various physics courses to residents, graduate students and trainees. I am involved in several research projects in adaptive therapy, particle therapy and image guidance. These projects span departments within our university as well as at other institutions. All these tasks come together to combine my love for solving engineering problems with my knowledge and research in radiation physics to ensure patient safety and continually advance patient care.


Resident, University of Iowa, Radiation Oncology (2014)

Postdoctoral Fellow, Washington University in St. Louis, Radiation Oncology (2012)

PhD, University of Wisconsin–Madison, Medical Physics (2011)

MS, University of Wisconsin–Madison, Nuclear Engineering and Engineering Physics (2009)

MS, University of Wisconsin–Madison, Medical Physics (2007)

BS, University of Wisconsin–Madison, Nuclear Engineering (2005)

Academic Appointments

Assistant Professor, Human Oncology (2014–pres.)

Selected Honors and Awards

Executive Education Grant, University of Wisconsin Department of Engineering Professional Development (2016)

Physicist Training Scholarship, American Brachytherapy Society (2013)

NIH Training Fellowship (2009–2011)

Vilas Travel Grant (2009, 2010)

Tau Beta Pi Engineering Honor Society (2005)

Boards, Advisory Committees and Professional Organizations

University of Wisconsin Medical Physics Residency Program Oversight Committee (2016–pres.)

American Association of Physicists in Medicine North Central Chapter Executive Committee (2016–pres.)

American Society for Radiation Oncology (2012–pres.)

American Association of Physicists in Medicine (2005–pres.)

Research Focus

Adaptive Radiotherapy, Image Registration, Informatics and Information Systems, MR-Guided Radiotherapy, Radiosurgery, Treatment Planning Systems


  • Secondary Neutron Dose from a Dynamic Collimation System During Intracranial Pencil Beam Scanning Proton Therapy: A Monte Carlo Investigation. Int J Radiat Oncol Biol Phys
    Smith BR, Hyer DE, Hill PM, Culberson WS
    2018 Aug 13; :
    • More

      Patients receiving pencil beam scanning (PBS) proton therapy with the addition of a Dynamic Collimation System (DCS) are potentially subject to additional neutron dose from interactions between the incident proton beam and the trimmer blades. This study investigates the secondary neutron dose rates for both single field uniform dose and intensity modulated proton therapy treatments. Secondary neutron dose distributions were calculated for both a dynamically collimated and uncollimated, dual-field chordoma treatment plan and compared to previously published neutron dose rates from other contemporary scanning treatment modalities. Monte Carlo N-Particle transport code was used to track all primary and secondary particles generated from nuclear reactions within the DCS during treatment through a model of the patient geometry acquired from the CT planning dataset. Secondary neutron ambient dose equivalent distributions were calculated throughout the patient using a meshgrid with a tally resolution equivalent to that of the treatment planning CT. The median healthy brain neutron ambient dose equivalent for a dynamically collimated intracranial chordoma treatment plan using a DCS was found to be 0.97 mSv/Gy, 1.37 mSv/Gy, and 1.24 mSv/Gy for the right lateral single field uniform dose (SFUD) field, apex SFUD field, and composite intensity modulated proton therapy distribution from two fields, respectively. This was at least 55 % lower than what has been reported for uniform scanning modalities with brass apertures but is still an increase in the excess relative risk of secondary cancer incidence compared to an uncollimated PBS treatment using only a graphite range shifter. Regardless, the secondary neutron dose expected from the DCS for these PBS proton therapy treatments appears to be on the order of, or below, what is expected for alternative collimated proton therapy techniques.

      View details for PubMedID 30114462
  • A New Era of Image Guidance with Magnetic Resonance-guided Radiation Therapy for Abdominal and Thoracic Malignancies. Cureus
    Mittauer K, Paliwal B, Hill P, Bayouth JE, Geurts MW, Baschnagel AM, Bradley KA, Harari PM, Rosenberg S, Brower JV, Wojcieszynski AP, Hullett C, Bayliss RA, Labby ZE, Bassetti MF
    2018 Apr 04; 10 (4): e2422
    • More

      Magnetic resonance-guided radiation therapy (MRgRT) offers advantages for image guidance for radiotherapy treatments as compared to conventional computed tomography (CT)-based modalities. The superior soft tissue contrast of magnetic resonance (MR) enables an improved visualization of the gross tumor and adjacent normal tissues in the treatment of abdominal and thoracic malignancies. Online adaptive capabilities, coupled with advanced motion management of real-time tracking of the tumor, directly allow for high-precision inter-/intrafraction localization. The primary aim of this case series is to describe MR-based interventions for localizing targets not well-visualized with conventional image-guided technologies. The abdominal and thoracic sites of the lung, kidney, liver, and gastric targets are described to illustrate the technological advancement of MR-guidance in radiotherapy.

      View details for PubMedID 29872602
  • Long-term dosimetric stability of multiple TomoTherapy delivery systems. J Appl Clin Med Phys
    Smilowitz JB, Dunkerley D, Hill PM, Yadav P, Geurts MW
    2017 May; 18 (3): 137-143
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      The dosimetric stability of six TomoTherapy units was analyzed to investigate changes in performance over time and with system upgrades. Energy and output were tracked using monitor chamber signal, onboard megavoltage computed tomography (MVCT) detector profile, and external ion chamber measurements. The systems (and monitoring periods) include three Hi-Art (67, 61, and 65 mos.), two TomoHDA (31 and 26 mos.), and one Radixact unit (11 mos.), representing approximately 10 years of clinical use. The four newest systems use the Dose Control Stability (DCS) system and Fixed Target Linear Accelerator (linac) (FTL). The output stability is reported as deviation from reference monitor chamber signal for all systems and/or from an external chamber signal. The energy stability was monitored using relative (center versus off-axis) MVCT detector signal (beam profile) and/or the ratio of chamber measurements at 2 depths. The clinical TomoHDA data were used to benchmark the Radixact stability, which has the same FTL but runs at a higher dose rate. The output based on monitor chamber data of all systems is very stable. The standard deviation of daily output on the non-DCS systems was 0.94-1.52%. As expected, the DCS systems had improved standard deviation: 0.004-0.06%. The beam energy was also very stable for all units. The standard deviation in profile flatness was 0.23-0.62% for rotating target systems and 0.04-0.09% for FTL. Ion chamber output and PDD ratios supported these results. The output stability on the Radixact system during extended treatment delivery (20, 30, and 40 min) was comparable to a clinical TomoHDA system. For each system, results are consistent between different measurement tools and techniques, proving not only the dosimetric stability, but also these quality parameters can be confirmed with various metrics. The replacement history over extended time periods of the major dosimetric components of the different delivery systems (target, linac, and magnetron) is also reported.

      View details for PubMedID 28464517
  • Dosimetric Comparison of Real-Time MRI-Guided Tri-Cobalt-60 Versus Linear Accelerator-Based Stereotactic Body Radiation Therapy Lung Cancer Plans. Technol Cancer Res Treat
    Wojcieszynski AP, Hill PM, Rosenberg SA, Hullett CR, Labby ZE, Paliwal B, Geurts MW, Bayliss RA, Bayouth JE, Harari PM, Bassetti MF, Baschnagel AM
    2017 Jun; 16 (3): 366-372
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      PURPOSE: Magnetic resonance imaging-guided radiation therapy has entered clinical practice at several major treatment centers. Treatment of early-stage non-small cell lung cancer with stereotactic body radiation therapy is one potential application of this modality, as some form of respiratory motion management is important to address. We hypothesize that magnetic resonance imaging-guided tri-cobalt-60 radiation therapy can be used to generate clinically acceptable stereotactic body radiation therapy treatment plans. Here, we report on a dosimetric comparison between magnetic resonance imaging-guided radiation therapy plans and internal target volume-based plans utilizing volumetric-modulated arc therapy.

      MATERIALS AND METHODS: Ten patients with early-stage non-small cell lung cancer who underwent radiation therapy planning and treatment were studied. Following 4-dimensional computed tomography, patient images were used to generate clinically deliverable plans. For volumetric-modulated arc therapy plans, the planning tumor volume was defined as an internal target volume + 0.5 cm. For magnetic resonance imaging-guided plans, a single mid-inspiratory cycle was used to define a gross tumor volume, then expanded 0.3 cm to the planning tumor volume. Treatment plan parameters were compared.

      RESULTS: Planning tumor volumes trended larger for volumetric-modulated arc therapy-based plans, with a mean planning tumor volume of 47.4 mL versus 24.8 mL for magnetic resonance imaging-guided plans ( P = .08). Clinically acceptable plans were achievable via both methods, with bilateral lung V20, 3.9% versus 4.8% ( P = .62). The volume of chest wall receiving greater than 30 Gy was also similar, 22.1 versus 19.8 mL ( P = .78), as were all other parameters commonly used for lung stereotactic body radiation therapy. The ratio of the 50% isodose volume to planning tumor volume was lower in volumetric-modulated arc therapy plans, 4.19 versus 10.0 ( P < .001). Heterogeneity index was comparable between plans, 1.25 versus 1.25 ( P = .98).

      CONCLUSION: Magnetic resonance imaging-guided tri-cobalt-60 radiation therapy is capable of delivering lung high-quality stereotactic body radiation therapy plans that are clinically acceptable as compared to volumetric-modulated arc therapy-based plans. Real-time magnetic resonance imaging provides the unique capacity to directly observe tumor motion during treatment for purposes of motion management.

      View details for PubMedID 28168936
  • Gadoxetate for direct tumor therapy and tracking with real-time MRI-guided stereotactic body radiation therapy of the liver. Radiother Oncol
    Wojcieszynski AP, Rosenberg SA, Brower JV, Hullett CR, Geurts MW, Labby ZE, Hill PM, Bayliss RA, Paliwal B, Bayouth JE, Harari PM, Bassetti MF
    2016 Feb; 118 (2): 416-8
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      SBRT is increasingly utilized in liver tumor treatment. MRI-guided RT allows for real-time MRI tracking during therapy. Liver tumors are often poorly visualized and most contrast agents are transient. Gadoxetate may allow for sustained tumor visualization. Here, we report on the first use of gadoxetate during real-time MRI-guided SBRT.

      View details for PubMedID 26627702
  • A method for modeling laterally asymmetric proton beamlets resulting from collimation. Med Phys
    Gelover E, Wang D, Hill PM, Flynn RT, Gao M, Laub S, Pankuch M, Hyer DE
    2015 Mar; 42 (3): 1321-34
    • More

      PURPOSE: To introduce a method to model the 3D dose distribution of laterally asymmetric proton beamlets resulting from collimation. The model enables rapid beamlet calculation for spot scanning (SS) delivery using a novel penumbra-reducing dynamic collimation system (DCS) with two pairs of trimmers oriented perpendicular to each other.

      METHODS: Trimmed beamlet dose distributions in water were simulated with MCNPX and the collimating effects noted in the simulations were validated by experimental measurement. The simulated beamlets were modeled analytically using integral depth dose curves along with an asymmetric Gaussian function to represent fluence in the beam's eye view (BEV). The BEV parameters consisted of Gaussian standard deviations (sigmas) along each primary axis (σ(x1),σ(x2),σ(y1),σ(y2)) together with the spatial location of the maximum dose (μ(x),μ(y)). Percent depth dose variation with trimmer position was accounted for with a depth-dependent correction function. Beamlet growth with depth was accounted for by combining the in-air divergence with Hong's fit of the Highland approximation along each axis in the BEV.

      RESULTS: The beamlet model showed excellent agreement with the Monte Carlo simulation data used as a benchmark. The overall passing rate for a 3D gamma test with 3%/3 mm passing criteria was 96.1% between the analytical model and Monte Carlo data in an example treatment plan.

      CONCLUSIONS: The analytical model is capable of accurately representing individual asymmetric beamlets resulting from use of the DCS. This method enables integration of the DCS into a treatment planning system to perform dose computation in patient datasets. The method could be generalized for use with any SS collimation system in which blades, leaves, or trimmers are used to laterally sharpen beamlets.

      View details for PubMedID 25735287

Contact Information

Patrick Hill, PhD

600 Highland Avenue, K4/B82
Madison, WI 53792-0001