ELogs/JamesGolbourn

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Electronic Log for James Golbourn


To Do

Short Term

  • Write research essay.
  • Update presentation with corrections made.
  • Better understand beam uniformity (is it a function of depth?) - The SOBP longitudinal uniformity is defined as the maximum difference in the dose within the dose reference volume expressed as the percentage of the average dose within the reference volume. Normally part of weekly QA.
  • Look at daily and monthly QA parameters.
  • AAPM Task group no.224 set to publish daily machine QA procedures - but not published yet.
  • Put links in wiki

Long Term

  • Get in contact with Laurent contact at Med Austrom about QA procedures.
  • Prepare practice presentation for project (8/2/19)
  • Write up report on meeting with UCLH.
  • Look at what functioning centres are using as QA.
  • Look at advantages and disadvantages of QA systems.

Tasks Completed

  • Presentation to PBT group.
  • Project progress report.
  • Project outline.
  • First plan for research essay.
  • Prepare practise presentation to Agapi.
  • Email Alison for details of Haakan Nystrom.
  • Met with Alison and Andrew form UCLH

Key Dates

Task Deadline
Project Outline 03/12/2018
Project Progress Report 31/01/2019
Short Presentation 08/02/2019
Research Essay 31/03/2019
Thesis Deadline 22/08/2019
Final Presentation 02/09/2019

Research Essay First Plan

  • Introduction:
  1. What is PBT and the theory?
    1. Different methods of beam production
    2. Pencil beam scanning and uniform scattering.
  2. What is Quality Assurance?
    1. Why is it needed?
    2. Relation to X-Ray QA and lack of consistency between facilities.
  3. Beam parameters - what needs to be measured
  • Sections on different beam properties and characteristics:
    • For each of these sections there should be a description of:
      • What is it?
      • Relation to patient dosimetry and why is it important?
      • Methods of measurement.
  1. Beam energy and range
  2. Beam output
  3. Spot size and symmetry
  4. Spot position and beam uniformity
  • Commercial devices available for QA
  1. IBA Lynx
  2. IBA Matrixx
  3. IBA Zebra
  4. Sun Nuclear QA 3
  • Various methods using these devices for QA
  • Conclusion

Second Meeting With Alison and Andrew

Firstly I updated Alison and Andrew on what progress I had made so far in my project. We briefly discussed some of the devices that I had come across as part of my research and the common beam characteristics that had been measured as part of daily QA.

From my Research

As before the characteristics measured as part of daily QA were:

  • The beam energy.
  • Output.
  • Spot position (not so much uniformity as difficult to do).
  • Spot size (and to an extent shape).

Summary of detectors:

  • Sun Nuclear DQA3: The DQA3 is a diode and ion chamber device used to measure the beam output, range, symmetry, spot position and size. Very useful device.
  • IBA Matrixx: Parallel plate chamber based device used to measure output, beam flatness and symmetry. Not as useful.
  • IBA Zebra: Multilayer ionization chamber device. Not as useful.
  • IBA Lynx: Scintillator based device used to measure spot size and position. Very useful device however limited due to cost.
  • IBA Sphinx and Lynx: Combination of Lynx and Sphinx used to measure spot position, size and range. Very useful but again limited by cost.
  • Gaffchromic film: Film based detector used to obtain dose profile.

Discussion

Andrew and Alison confirmed that they planned to initially use the Sun Nuclear DQA3 device for their daily QA measurements. This decision was based on a compromise between cost and which measurements could be carried out. The IBA Lynx and Sphinx is the "gold standard" in daily QA systems however would cost roughly £500,000 which is not feasible. Conversely, the DQA3 device is about £8,000 and has the capability to perform the required measurements.

The output and range measurements are carried out using the central 5 ionization chambers and the spot position and size with the diodes. The range measured is a measure of range fluctuations rather, this is sufficient for daily QA. Different buildups are placed in front of the ionization chambers to allow for different range measurements. The diodes used are at a set depth and position and so get limited information from them but could be sufficient for daily QA. To measure the position the beam is directed at the innermost diode of the triplet and a half Gaussian is constructed by the detection from the triplet of diodes. This is combined with the half Gaussian obtained from the triplet on the opposite side and if the combined shape is roughly Gaussian then that acts as a confirmation of spot position. There are difficulties measuring the spot size as the beam will not be circular when measured, and, for example, could be elliptical in shape and there are therefore difficulties in obtaining the size directly (a scintillator would be better to get size).

The spots delivered are ideally Gaussian, and the spots should be separated such that the intensity is constant to roughly 2/3 %. The intensity cannot be measured with the DQA3. The intensity distribution is very sensitive to spot position deviations. Small changes in the spot position can greatly effect the uniformity of the intensity distribution. This increases the precision at which the position must be measured.

In order to activate the DQA3, the central axis chamber, used to measure the output, must be irradiated to trigger measurements. Can either irradiate the whole surface and perform measurements. Or quickly perform measurements on diodes after irradiation. One option is to obtain multiple data sets/ fields and then put together to reconstruct data.

Monthly QA was also discussed but they did not have an ideal set of measurements to take for this and is dependent on what they get out the daily QA. One option is to use the Zebra (multilayer ionization chamber).

From daily QA, the goal was to look for big deviations for the energy, beam profile and output, apart from with the spot spacing (position).

For me to potentially work on in the future:

  • Look at putting different build up in front of the chambers to generate different depths. The buildups are made up of plastic WET material. In the patient the dose distribution is dominated by the scattering interactions rather than the beam energy.
  • Look at doing a DQA3 prototype and maybe test it in Denmark.

Progress Report Outline

  • Introduction to Proton beam therapy.
  • What is Quality Assurance?
  • Important beam characteristics.
  • Commercially available devices such as the Matrixx, Lynx and Sun Nuclear QA3.
  • Other methods for measuring beam properties.

Comments made about presentation

  • Understand what range modulators do.
  • Look into whether Zebra was initially designed for X-Rays.
  • Zebra not often used for daily QA due to the very long initial set up time.
  • Investigate film dosimetry e.g Gafchromic film.
  • Research Lynx scintillator.
  • Range calorimeter - need a moving absorber, e.g water tank, to measure energy and range.
  • Know difference between scintillator screens and fibres - fibres use fibre optics and are not used due to needing something to read output from each fibre which is expensive.
  • UCLH will have 4 treatment rooms.
  • Put slide number on presentation.
  • Expand on each daily QA:
    • Table of devices
    • Tolerances
    • How long it takes
  • Collect standards and tolerances on energy, spot size and output.

Useful Links for Research Essay

Devices and Detectors



  • IBA Matrixx
    • Use of a two-dimensional ionization chamber array for proton therapy beam quality assurance, B Arjomandy Et al, Med Phys. 2008 Sep;35(9):3889-94
      • Method describing how the Matrixx can be used for measuring beam flatness and symmetry.
    • Quality assurance of carbon ion and proton beams: A feasibility study for using the 2D MatriXX detector, M Donetti Et al, Phys Med. 2016 Jun;32(6):831-7. doi: 10.1016/j.ejmp.2016.05.058. Epub 2016 May 28 .
      • Matrixx can be used to replace film dosimetry.


  • IBA Lynx
    • Characterization of a commercial scintillation detector for 2-D dosimetry in scanned proton and carbon ion beams, S Russo et al, Physica Medica Volume 34, February 2017.
      • Investigates using the Lynx to measure spot size and position. Lynx can be used due to high spatial resolution.


  • IBA Lynx and Sphinx
    • Range resolution and reproducibility of a dedicated phantom for proton PBS daily quality assurance, Zeitschrift für Medizinische Physik, Vol 28, Issue 4, December 2018.
      • Investigates combining the Sphinx and Lynx together for daily QA. The combination can be used to measure relative range using the Sphinx blocks as well as spot size and position with Lynx.


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