The Effect of Patient Motion on Electronic Portal Imaging Dosimetry during Radiotherapy Treatments of Cancer

Overview

Topic status: We're looking for students to study this topic.

This project is part of a broader project to investigate and develop the use of electronic portal imaging devices (EPID's) for verification of the delivered dose in complex radiotherapy treatments such as Intensity Modulated Radiotherapy (IMRT).

Hypothesis/Aims: The project will through measurement and Monte-Carlo simulation investigate how variations in dose delivery and patient motion affect the measured EPID portal dose. An understanding of these motion effects is crucial to assessing the accuracy of the technique.

Approaches: An ongoing collaborative project between research physicists at QUT and clinical physicists at the Princess Alexandra Hospital has produced Monte-Carlo models of the response of the EPID to the modulated incident fluence for IMRT treatments, with either no patient in the field or with a static model of the patient (CT data) in the field. Patients are however, not static, there are variations in their day to day set-up and there are variations during each fraction e.g. due to respiratory motion. These effects mean that the static CT model of the patient acquired for planning will not be an accurate representation of their position and internal anatomy during treatment. These would be expected to be of more significance in the thoracic region where respiratory motion is significant. This will manifest as a difference between the predicted and measured portal dose. There is very little evidence of what the significance of set-up errors and intra-fraction motion will be on the EPID dose and this is something we will address with this project. The effect of patient set-up errors will be simulated by applying shifts to the CT data that is used for the Monte-Carlo dose predictions. The effect of the shift will be investigated on the predicted EPID dose. This will allow us to assess the sensitivity of the EPID dose to set-up errors that would typically occur during a treatment. Intra-fractional motion will be investigated by placing phantoms on a moving platform to simulate respiratory motion. A moving irregularly shaped inhomogeneous phantom will give a different 2D EPID dose distribution to the same phantom imaged in a static position. This will allow the effect of this motion on the measured EPID dose to be investigated and compared with simulations.

The project will involve Monte-Carlo simulations of the radiation transport of high energy x-ray beams in radiotherapy treatments using QUT high performance computing resources and experimental work at the Princess Alexandra Hospital.

References:

  • A.L Boyer, M. Goitein, A.J. Lomax and E.S. Pedroni Radiation in the Treatment of Cancer Physics Today, September 2002, p. 34-36
  • W. van Elmpt et al A literature review of electronic portal imaging for radiotherapy dosimetry, Radiotherapy and Oncology Vol 88, p. 289-309 (2008)
  • F. Verhaegen and J. Seuntjens Monte-Carlo Modelling of External Radiotherapy Photon Beams, Physics in Medicine and Biology, Vol 48, p. R107-R164 (2003)
Study level
Honours
Supervisors
QUT
Organisational unit

Science and Engineering Faculty

Research area

Physics

Contact

Please contact the supervisor.