University of Wisconsin–Madison
Sean Frigo headshot

Sean Frigo, PhD

Assistant Professor

Department of Human Oncology

My primary focus is on clinical care, and within that area, the implementation and management of treatment planning systems. We are leveraging new software technologies to bring all relevant patient information and data into one environment in order to facilitate treatment plan design. This not only applies to calculating treatment dose, but also supporting the development of calculating other quantities, such as treatment response. To support research initiatives in these areas, we have established a separate dedicated treatment planning environment that provides a sandbox in order to develop and test new approaches to treatment planning.

I engage in many informal teaching activities, from mentoring medical physics residents to serving as guest lecturer in medical physics courses. I also work with undergraduates in the Biomedical Engineering Department on medical equipment development projects. Given my background working in the medical device industry, I am actively involved in ASTRO professional organization committees and sub-committees.


Alexander von Humboldt Fellow, Technical University of Munich, X-Ray Photodissociation (1997)

PhD, University of Wisconsin–Madison, X-Ray Photodissociation (1994)

BS, University of Wisconsin–Platteville, Chemistry, Mathematics, Physics (1988)

Academic Appointments

Assistant Professor, Human Oncology (2014)

Clinical Adjunct Professor, Medical Physics (2007)

Selected Honors and Awards

Alexander von Humboldt Fellowship (1994)

Society of Physics Students Scholarship (1987)

Chicago Drug and Chemical Association Scholarship (1986)

Leo E. Boebel Memorial Scholarship (1984–1987)

Lawson Products Company Scholarship (1983)

Boards, Advisory Committees and Professional Organizations

ASTRO Corporate Relations Committee (2017)

ASTRO Congressional Relations Sub-committee (2017)

The best treatments are ones that model the right amount of dose in the right place at the right time and accurately predict the effects of those treatments.

Activities that advance treatment planning call for a dedicated environment that closely mimics that used for patient care, yet can tolerate being broken. My research activities are aimed at providing such a resource in order for us to develop new planning techniques and patient treatment models.

Clinical Treatment Planning System

Our problem definition is inspired by asking what we can do better for our current patients and what we would want to do if we just had the right tools on hand. Thus, significant effort is being spent on implementing a new clinical treatment planning system for patient care. This will lay the groundwork for research in adaptive therapy and improved patient modeling.


An important effort going forward is the development of medical device management techniques to manage the clinical treatment planning system. By applying modern concepts of change and state management, we are able to demonstrate system stability and calculation accuracy as we upgrade software modules or change configurations.

Non-clinical Treatment Planning System

We are implementing a second treatment planning system that closely mimics the one we are using for patient care. Within this dedicated system, we can rapidly prototype and test new planning modules and techniques. It is important that the planning system for patient care be tightly controlled and limited changes be thoroughly tested prior to use. Thus it is important to do developmental work in a separate system that can tolerate being broken and subsequent down time, but also be subject to less rigorous controls and testing.


We intend to utilize this sandbox environment to improve how we perform adaptive planning. Through the use of CT, MR and PT imaging, we are able to build three-dimensional maps of a patient’s anatomy, identifying organs and tissues. We also can create corresponding three-dimensional maps of radiation treatment dose, showing where the radiation energy is deposited. We need to extend these capabilities to be able to do so as a patient’s anatomy changes over time, either during a single treatment course in the time-frame of weeks or during multiple courses over years. We need software and data frameworks to support this time element.

Planning unification

We employ three distinct external beam delivery technologies here at the University of Wisconsin (TrueBeam, Tomotherapy, ViewRay) in addition to brachytherapy. Each technology we use to deliver radiation dose currently has its own dedicated treatment planning system. However, each one of these systems is a data island.


Often, it is best to be able to use different delivery technologies in a single treatment course, such as boosting a prostate with HDR brachytherapy after an initial external beam treatment. It takes great manual effort to copy data between islands in order to create a plan that reflects the entire treatment course and to optimize the different plans over the treatment course. By supporting all treatment modalities within one planning environment, we can calculate and combine dose easily in order to explore the best treatment options for our patients.

  • Implementation of the validation testing in MPPG 5.a "Commissioning and QA of treatment planning dose calculations-megavoltage photon and electron beams". J Appl Clin Med Phys
    Jacqmin DJ, Bredfeldt JS, Frigo SP, Smilowitz JB
    2017 Jan; 18 (1): 115-127
    • More

      The AAPM Medical Physics Practice Guideline (MPPG) 5.a provides concise guidance on the commissioning and QA of beam modeling and dose calculation in radiotherapy treatment planning systems. This work discusses the implementation of the validation testing recommended in MPPG 5.a at two institutions. The two institutions worked collaboratively to create a common set of treatment fields and analysis tools to deliver and analyze the validation tests. This included the development of a novel, open-source software tool to compare scanning water tank measurements to 3D DICOM-RT Dose distributions. Dose calculation algorithms in both Pinnacle and Eclipse were tested with MPPG 5.a to validate the modeling of Varian TrueBeam linear accelerators. The validation process resulted in more than 200 water tank scans and more than 50 point measurements per institution, each of which was compared to a dose calculation from the institution's treatment planning system (TPS). Overall, the validation testing recommended in MPPG 5.a took approximately 79 person-hours for a machine with four photon and five electron energies for a single TPS. Of the 79 person-hours, 26 person-hours required time on the machine, and the remainder involved preparation and analysis. The basic photon, electron, and heterogeneity correction tests were evaluated with the tolerances in MPPG 5.a, and the tolerances were met for all tests. The MPPG 5.a evaluation criteria were used to assess the small field and IMRT/VMAT validation tests. Both institutions found the use of MPPG 5.a to be a valuable resource during the commissioning process. The validation testing in MPPG 5.a showed the strengths and limitations of the TPS models. In addition, the data collected during the validation testing is useful for routine QA of the TPS, validation of software upgrades, and commissioning of new algorithms.

      View details for PubMedID 28291929
  • Photoabsorption study of Bacillus megaterium, DNA and related biological materials in the phosphorus K-shell edge region. Radiat Res
    Frigo SP, McNulty I, Richmond RC, Ehret CF
    2004 Oct; 162 (4): 464-8
    • More

      We measured the X-ray transmission spectra of several biologically related samples in the phosphorus K-shell edge absorption region. These include red phosphorus, hydrated sodium phosphate (Na(3)PO(4).12 H(2)O), deoxyribonucleic acid (DNA), adenosine triphosphate (ATP), diolylphosphatidyl choline (DOPC), and Bacillus megaterium spores. Red phosphorus essentially displays an edge-jump. All other spectra are similar in form and energy position: Each is dominated by a narrower, more intense first peak and a broader but less intense second peak. The corresponding K-shell edge absorption thresholds are shifted toward higher energy relative to that for red phosphorus, as expected for increasing degrees of phosphorus oxidation. The B. megaterium spectrum has aspects common to both the phosphate and DNA spectra and is therefore interpreted as a composite of spectra arising from DNA, ribonucleic acid (RNA) and phosphates within the spore. The B. megaterium spore spectrum provides information for resonant radiation damage studies in the phosphorus K-shell edge absorption region by identifying candidate photoexcitations. In addition, the absorption spectra will be useful in X-ray microscopy and macromolecular crystallography studies at the phosphorus K-shell edge.

      View details for PubMedID 15447035
  • Atom-selective bond breaking in a chemisorbed homonuclear molecule induced by core excitation: N2/Ru(001) Phys Rev Lett
    Romberg R, Heckmair N, Frigo SP, Ogurtsov A, Menzel D, Feulner P
    2000 Jan 10; 84 (2): 374-7
    • More

      We observe photochemical selectivity for N 1s to pi(*) excitations of chemisorbed N2. By narrow bandwidth synchrotron radiation we selectively excite one of the two atoms of the molecule. Photon stimulated desorption of neutral N atoms predominates for excitations of the N atom close to the surface, whereas excitation of the outer atom ejects predominantly N02 and small amounts of N+, demonstrating the predominant breaking of the inner or outer bond, respectively, of the N2 adsorbate. Analysis on the basis of previously obtained decay electron spectra after atom-selective excitation can explain the mechanism of localized bond breaking.

      View details for PubMedID 11015914
  • Partial photoionization cross sections and photoelectron angular distributions for double excitations up to the N=5 threshold in helium. Phys Rev A
    Menzel A, Frigo SP, Whitfield SB, Caldwell CD, Krause MO
    1996 Sep; 54 (3): 2080-2090
  • Decay Paths of Interfering Two-Electron Excitations in Helium. Phys Rev Lett
    Menzel A, Frigo SP, Whitfield SB, Caldwell CD, Krause MO, Tang JZ, Shimamura I
    1995 Aug 21; 75 (8): 1479-1482


Contact Information

Sean Frigo, PhD

600 Highland Ave,
Madison, WI 53792