Headshot of Gemma Davies

Gemma Davies, PhD, DABR

Assistant Professor (CHS)

Department of Human Oncology

I am a medical physicist board-certified in radiation oncology in both the U.K., where I did my initial training, and the U.S. My primary focus is ensuring that patient treatments are executed correctly and safely through comprehensive review of radiation treatment plans and quality assurance of the treatment machines used to deliver radiation. I am also focused on providing physics support for clinical trial execution and data management within the Department of Human Oncology.

Education

ABR Structured Mentorship, Johns Hopkins University, Therapeutic Medical Physics (2018)

PhD, Institute of Cancer Research & Royal Marsden Hospital, Medical Physics (2013)

MSc, King's College London, Medical Engineering & Physics (2004)

BSc, Imperial College London, Physics (2002)

Academic Appointments

Assistant Professor (CHS), Department of Human Oncology (2021)

Boards, Advisory Committees and Professional Organizations

American Board of Radiology (2018 - pres.)

American Association of Physicists in Medicine (2018 – pres.)

UK Health and Professions Council (2007 – pres.)

UK Institute of Physics and Engineering in Medicine (2002 – pres.)

Clinical Focus

External beam radiotherapy, clinical trials data management, linear accelerator quality assurance.

  • An experimental evaluation of the Agility MLC for motion-compensated VMAT delivery Physics in medicine and biology
    Davies GA, Clowes P, Bedford JL, Evans PM, Webb S, Poludniowski G
    2013 Jul 7;58(13):4643-57. doi: 10.1088/0031-9155/58/13/4643.
    • More

      An algorithm for dynamic multileaf-collimator (dMLC) tracking of a target performing a known a priori, rigid-body motion during volumetric modulated arc therapy (VMAT), has been experimentally validated and applied to investigate the potential of the Agility (Elekta AB, Stockholm, Sweden) multileaf-collimator (MLC) for use in motion-compensated VMAT delivery. For five VMAT patients, dosimetric measurements were performed using the Delta(4) radiation detector (ScandiDos, Uppsala, Sweden) and the accuracy of dMLC tracking was evaluated using a gamma-analysis, with threshold levels of 3% for dose and 3 mm for distance-to-agreement. For a motion trajectory with components in two orthogonal directions, the mean gamma-analysis pass rate without tracking was found to be 58.0%, 59.0% and 60.9% and was increased to 89.1%, 88.3% and 93.1% with MLC tracking, for time periods of motion of 4 s, 6 s and 10 s respectively. Simulations were performed to compare the efficiency of the Agility MLC with the MLCi MLC when used for motion-compensated VMAT delivery for the same treatment plans and motion trajectories. Delivery time increases from a static-tumour to dMLC-tracking VMAT delivery were observed in the range 0%–20% for the Agility, and 0%–57% with the MLCi, indicating that the increased leaf speed of the Agility MLC is beneficial for MLC tracking during lung radiotherapy.

      PMID:23780400 | DOI:10.1088/0031-9155/58/13/4643


      View details for PubMedID 23780400
  • An experimental comparison of conventional two-bank and novel four-bank dynamic MLC tracking Physics in medicine and biology
    Davies GA, Clowes P, McQuaid D, Evans PM, Webb S, Poludniowski G
    2013 Mar 7;58(5):1635-48. doi: 10.1088/0031-9155/58/5/1635. Epub 2013 Feb 19.
    • More

      The AccuLeaf mMLC featuring four multileaf-collimator (MLC) banks has been used for the first time for an experimental comparison of conventional two-bank with novel four-bank dynamic MLC tracking of a two-dimensional sinusoidal respiratory motion. This comparison was performed for a square aperture, and for three conformal treatment apertures from clinical radiotherapy lung cancer patients. The system latency of this prototype tracking system was evaluated and found to be 1.0 s and the frequency at which MLC positions could be updated, 1 Hz, and therefore accurate MLC tracking of irregular patient motion would be difficult with the system in its current form. The MLC leaf velocity required for two-bank-MLC and four-bank-MLC tracking was evaluated for the apertures studied and a substantial decrease was found in the maximum MLC velocity required when four-banks were used for tracking rather than two. A dosimetric comparison of the two techniques was also performed and minimal difference was found between two-bank-MLC and four-bank-MLC tracking. The use of four MLC banks for dynamic MLC tracking is shown to be potentially advantageous for increasing the delivery efficiency compared with two-bank-MLC tracking where difficulties are encountered if large leaf shifts are required to track motion perpendicular to the direction of leaf travel.

      PMID:23422212 | DOI:10.1088/0031-9155/58/5/1635


      View details for PubMedID 23422212
  • MLC tracking for Elekta VMAT: a modelling study Physics in medicine and biology
    Davies GA, Poludniowski G, Webb S
    2011 Dec 7;56(23):7541-54. doi: 10.1088/0031-9155/56/23/013. Epub 2011 Nov 11.
    • More

      A model has been developed to simulate volumetric modulated arc therapy (VMAT) delivery for Elekta control systems. The model was experimentally validated for static-tumour VMAT delivery and has been applied to the investigation of motion compensation with dynamic multileaf collimator (dMLC) delivery tracking for a series of VMAT lung treatment plans at various control point spacings for five patients. The relative increase in treatment time with dMLC tracking was calculated for four 1D rigid-body motion trajectories, and the effect of the control point spacing, the MLC leaf speed and an increased number of dose levels on the dMLC tracking delivery time evaluated. It has been observed that a faster leaf speed is advantageous for motion trajectories with shorter time periods and larger amplitudes. The accuracy of dMLC tracking was found to increase with a decreased control point spacing and is dependent on the amplitude and time period of the motion trajectory of the target. dMLC tracking is shown to be a promising emerging technology which can confer advantage over breath-hold motion-compensation techniques which more drastically reduce the efficiency of VMAT and are more invasive for the patient.

      PMID:22079979 | DOI:10.1088/0031-9155/56/23/013


      View details for PubMedID 22079979
  • Electron dosimetry of angular fields The British journal of radiology
    Davies G, Bidmead M, Lamb C, Nalder C, Seco J
    2007 Mar;80(951):202-8. doi: 10.1259/bjr/86992777. Epub 2007 Feb 15.
    • More

      Shaping electron fields through the use of lead cut-outs may result in there being acute angles in part of the field. Using both experimental techniques and EGSnrc Monte Carlo simulations an investigation was carried out to determine the dosimetric consequences of this. Measurements were made to investigate how the field dose was related to the angle between adjacent sides in the cut-outs. The study involved two electron energies (9 MeV and 12 MeV) and source-skin distances (SSDs) in the range 1000-1100 mm. For angles less than about 120 degrees the dose received in the angular region decreased significantly, the effect being more pronounced at 12 MeV than at 9 MeV, and at longer SSDs. The planar shapes of the Monte Carlo dose distributions agreed with those experimentally determined to within +/-1.5 mm at 9 MeV and +/-1.0 mm at 12 MeV, demonstrating the validity of using such calculations for this purpose. Graphs are presented which may help in the prospective assessment of the dose reductions likely to be incurred.

      PMID:17303615 | DOI:10.1259/bjr/86992777


      View details for PubMedID 17303615

Contact Information

Gemma Davies, PhD, DABR

600 Highland Avenue,
Madison, WI 53792