The Effect of Patient Motion on Electronic Portal Imaging Dosimetry during Radiotherapy - Research Proposal Example

Name Topic: The Effect of Patient Motion on Electronic Portal Imaging Dosimetry during Radiotherapy Treatments of Cancer Supervisor (s) The Effect of Patient Motion on Electronic Portal Imaging Dosimetry during Radiotherapy Treatments of Cancer 1.0 Introduction Electronic Portal Imaging Devices (EPIDs) were earlier developed and designed as a replacement for radiographic film for geometric verification of patient setup during treatment. Nevertheless, their uses have been advanced and are also used for acquiring dosimetric information of the radiation treatment. Acquiring this information is either done by in vivo dosimetry or pretreatment verification (Herman, Kruse & Hagness, 2000). Employment of EPIDs for setup verification in the clinic is very limited worldwide, and vendors have offered little support to invest widely in dosimetry applications. Verification of the dose in 2-D or 3-D is complicated, which is extremely important if portal dosimetry will be used as an independent check of the treatment planning system. Another reason why the use of EPIDs for setup verification is limited is because most clinical departments have inadequate resources for the development of portal dosimetry software. The EPID provides an effective and efficient method for defining radiation field placement accuracy. It has the capability of capturing images at every single treatment, and it can also capture multiple images during every treatment with much ease. For the past few years, EPID software and hardware have advanced to a point where EPIDs driven by the computer can replace film imaging and provide quality information, thus reducing errors and improving clinical results. The main aim of this study is to investigate the effect of patient motion on Electronic Portal Imaging Dosimetry during radiotherapy treatments of cancer 2.0 Aims and Objectives The main aim of this study is to investigate how variations in patient motion and dose delivery affect the measured EPID portal dose. This investigation will be achieved through measurement and Monte-Carlo simulation. Understanding the effects of these motions will assist in assessing the accuracy of the technique. 3.0 Problem Statement Patients are never static there are variations in every instance, and there are also variations in their daily setup. A good example of the cause of variations is the respiratory motion. The effects of the variations in patient motion produce an inaccurate static CT model of the patient since it does not represent their accurate position and internal anatomy during treatment. Thoracic region will experience such misrepresentation a lot due respiratory motion. This misrepresentation will reflect as a difference between the measured and predicted portal dose. The main purpose of this study is to address the significance of setup errors and intra-fraction motion on the EPID dose. This study will involve Monte-Carlo simulations of the radiation transport of high energy x-ray beams in radiotherapy treatments. This study should be attempted so as to understand both positive and negative effect of patient motion on Electronic Portal Imaging Dosimetry during radiotherapy treatments of cancer. This understanding will assist the researcher in possibly devising ways to eliminate the negative effects caused by of setup errors and intra-fraction motion. 4.0 Literature Review This section will present an overview of work done previously that provides the required background for this research purposes. It will concentrate on various Electronic Portal Imaging Dosimetry topics and the effects of setup errors and intra-fraction motion on the EPID dose. This section will begin with a thorough coverage of Electronic Portal Imaging Dosimetry topics which will assist in setting the context of this research. 4.1 EPID Systems Present EPID systems are not as cumbersome to operate as earlier ones, which required the presence of a technical expert to guide users. Present EPID systems also offer better resolution and faster response as compared to earlier ones, which were using scintillators, diodes or liquid-based chambers. The control and analysis software used in EPID allows for efficient and quantitative use of these systems. The software must integrate viewer display, image assessment, image processing, image acquisition, and hardware manipulation. Analysis tools facilitate computer-assisted or manual analysis in 2-D or 3-D and automate field edge detection performed either off-line or on-line (McDermott et al., 2004). The computer-assisted tools eliminate the inconsistency, time-consuming and qualitative aspects of visual inspection endemic to film portal imaging. The EPID technology development was started in the 1950’s, even though its commercialization and widespread use began in 1980’s. Although EPID was originally designed as an imager, its usage as a dosimeter was quickly appreciated [Sea12]. Despite the increased interest, EPID dosimetry has not been utilized fully. The only dosimetric application that has been commercialized and extensively used is the simplest of all, through-air radiation fluence measurement. The advanced and useful features such as in vivo or transit dosimetry are only in use in a few major universities and medical centers. Commercial EPID manufacturers have also neglected the use of EPID in dosimetry because they have continued optimizing their designs towards radiographic imaging and ignoring dosimetry. Hardware issues such as backscatter and buildup depth also complicate EPID dosimetry. The detection layer is found in the buildup region of the linac’s megavoltage x-ray beam at an approximately water equivalent depth of 8mm. This region is an inconvenient region to acquire data since the dose changes rapidly with depth. According to Berry (2012), the hardware should be modified to include an additional buildup material so as to support dosimetry. The additional buildup material will present the following two advantages; first, it will move the measurement point to a more stable depth allowing for data acquisition, second, it will theoretically attenuate low energy scatter originating from the patient. Another hardware modification would be adding a shielding material to prevent backscattered radiation from entering detection layer. The backscatter sources lateral of the cassette include electronic cables, positioning motors, support arm, and EPID housing. These materials are known to contribute to an error of 5% to 6% in the dose measured, depending on the position and field size. Software attributes such as the imager calibration procedure also complicate dosimetry. Although software and hardware complications exist, these issues can be solved. The success of EPID through-air dosimetry and in the realms of imaging indicates that continued research in in vivo and transit dosimetry will have a positive outcome[Sea12]. Recently EPIDs are the preferred tools for verification of patient positioning in radiotherapy. Many researchers have investigated the usage of EPID images for radiotherapy dose measurement as they contain dose information. Since the introduction of amorphous-silicon EPIDs in 2000, the concern in Electronic Portal Image Device dosimetry has increased because of the favorable features such as potential for in vivo measurements and 3-D dose verification, digital format, high resolution, and faster image acquisition (Elmpt et al., 2008). A greater number of clinics are currently making use of EPIDs in in vivo dosimetry, pretreatment dose verification and quality control of linear accelerator. The use of EPIDs in dosimetry field has developed, and it is currently considered the most reliable and accurate dose verification method that can be applied in quite a large number of conditions. EPID dosimetry plays an important role in the verification procedures that are applied in a radiotherapy section. It provides a full account of dose delivered as well as a safety net for advanced to simple treatments (Elmpt et al., 2008). 4.2 Monte Carlo Simulation Presently, Monte Carlo dose calculation engines are in use in commercial treatment software because it is believed that this method can provide accuracy within 2% to 3% (Reynaert et al., 2006). By the year 2006, there were four general purpose Monte Carlo systems in use for radiotherapy dose calculation. These systems include Electronic Gamma Shower (EGS), Monte Carlo Neutron Photon (MCNP), Penetration and Energy Loss of Positron and Electron (PENELOPE), and Geometry and Tracking (GEANT) (Reynaert et al., 2006). PENELOPE and EGS stimulate the coupled transport of electrons and photons (and positrons), while other particles such as protons or neutrons are not considered. Advantage of these systems is that during the development of these codes, all attention will be focused on the particles of interest for radiotherapy dose planning. A disadvantage of the two systems is that, in high energy photon beams, the production of protons and neutrons in the accelerator head may affect the physical dose distribution in the patient. However, this can be rectified through the use of GEANT and MCNP systems. A crucial requirement for productive radio therapy is that the disagreements between dose distributions computed at the Treatment Planning (TP) stage and dose served to the patient are reduced. One of the most important components in the TP process is the precise calculation of dose distribution. The best method to achieve this accuracy is by the use of Monte Carlo calculation of particle transport (Nijsten et al., 2007). The Monte Carlo calculation of particle transport is normally done first in the geometry of the internal or external source, and then this is followed by the transport and energy disposition in the tissues concerned. In addition, Monte Carlo simulations also allow someone to examine the influence of source components on beams of a particular type and their contamination particles (Vehaegen & Seuntjens, 2003). 5.0 Method This section will address how the research will be carried out, and methods to be used to gather the required information. This section will also address the limit of the study and the data needed to collect. Justification of the methods used to collect the data will also be addressed in this section. Participants of this research will include people who have prior knowledge concerning Electronic Portal Image Device dosimetry. The effect of patient setup errors will be investigated by simulation. This simulation will be conducted by applying shifts to the Computed Tomography (CT) data that is used for Monte Carlo dose prognostications. The shift effect will be examined on the prognosticated EPID dose. This will assist in assessing the sensitivity of the EPID dose setup errors that would occur during a treatment. Intra- fraction motion will be examined through placing phantoms on a moving platform. This will be done to simulate the respiratory motion. A moving asymmetrical nonuniform phantom will give a different two dimension EPID dose distribution to the very phantom imaged in a static position. This will help in examining and comparing the effect of this motion on the measured EPID dose with simulation. Both qualitative and quantitative data collections methods will be applied in this research. The qualitative data for this research will be collected by studying the relevant literature concerning Electronic Portal Image Device dosimetry and any other relevant material that will assist in accomplishing the research. I also intend to use the interview method of qualitative data collection. Studying the relevant literature concerning Electronic Portal Image Device dosimetry will set the background of the research. This step will give a clear picture of what research is intended to achieve. It will also set the direction of the research as the technology which is supposed reviewed will be well analyzed. The interview method will be employed as a backup of what will be collected from the first step. This method will also assist in gathering first-hand information from someone who has a hand experience on the effects of patient motion Electronic Portal Image Device dosimetry during radiotherapy treatments of cancer. The people who will be interviewed will include those who have prior knowledge in Electronic Portal Image Device dosimetry including my supervisors. 5.1 Data Analysis The quantitative data of this research will be analyzed using numerical and statistical analysis. SPSS and MS-Excel programs will be used to represent the data using graphical methods such as histograms, pie charts, tables etc. (Agresti, 2002). These programs will also assist in carrying out validity tests so that a concise conclusion can be drawn. The qualitative data will be analyzed through an extensive review of the literature. This will help in understanding what others have done concerning in areas related to the research. This will give me as researcher insight and knowledge required to make necessary decisions during data collection. The interview qualitative data will be analyzed using the discourse analysis. 6.0 Equipment Computing resources are available at QUT, and for experimental work, the supervisors will organize which hospital we shall use. 7.0 Time Period Required S/NO. Task Duration Start Finish 1 Research proposal preparation 5 days 23/10/2012 28/10/2012 2 Searching the literature 6 days 29/10/2012 03/11/2012 3 Reviewing the literature 12 days 04/11/2012 16/11/2012 4 Drafting research methods 8 days 17/11/2012 25/11/2012 5 Meeting with the supervisor 3 days 26/11/2012 29/11/2012 6 Scheduling interviews 6 days 30/11/2012 05/12/2012 7 Data collection 4 days 06/12/2012 10/12/2012 8 Data analysis 7 days 11/12/2012 18/12/2012 9 Data discussion and evaluation 8days 19/12/2012 27/12/2012 10 Final draft preparation 10 days 28/12/2012 07/01/2013 11 2nd meeting with the supervisor for approval 3 days 08/01/2013 11/01/2013 12 Proofreading and correcting grammatical errors 2 days 12/01/2013 14/01/2013 13 Printing and binding 1 day 15/01/2013 16/01/2013 14 Submitting the final copies 1 day 17/01/2013 8.0 Costs Type of expenses Amount in $ Typing expenses 65 Printing expenses 50 Personal expenses 200 Research expenses 155 Total 470 9.0 Ethical Approval Ethical approval will be a requirement since the project will involve human experimentation. The approval will be acquired from the QUT Research Ethics Committee and the ethics committee of the recommended hospital. 10.0 Conclusion Employment of EPIDs for setup verification in the clinic is very limited worldwide, and vendors have offered little support to invest widely in dosimetry applications. However, the use of EPIDs in dosimetry field has developed, and it is currently considered the most reliable and accurate dose verification method that can be applied in quite a large number of conditions. EPID dosimetry plays an important role in the verification procedures that are applied in a radiotherapy section. It provides a full account of dose delivered as well as a safety net for advanced to simple treatments. The main aim of this study is to investigate how variations in patient motion and dose delivery affect the measured EPID portal dose. This investigation will be achieved through measurement and Monte-Carlo simulation. Understanding the effects of these motions will assist in assessing the accuracy of the technique. References Sea12: , (Berry, 2012), Sea12: , (Berry, 2012), Read More