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Verification of Dose Calculation Algorithms in Treatment Planning Systems for External Radiation Therapy: A Monte Carlo Approach

Wieslander, Elinore LU (2006)
Abstract (Swedish)
Popular Abstract in Swedish

För många cancerpatienter är strålbehandling ett viktigt behandlingsalternativ. En framgångsrik behandling kräver att den absorberade dosen till patienten kan ges med stor noggrannhet. Detta eftersom en liten avvikelse i absorberad dos kan påverka behandlingens resultat. Strålbehandling sker idag med avancerad teknik och utrustning där osäkerheterna i varje led i behandlingskedjan måste minimeras.



Ett led i förberedelserna är att beräkna den absorberade dosen till patienten. Detta görs idag med avancerade datorprogram, så kallade dosplaneringssystem. Noggrannheten i den beräknade dosen har vanligtvis studerats med experimentella mätningar. Experimentella data begränsas av vad... (More)
Popular Abstract in Swedish

För många cancerpatienter är strålbehandling ett viktigt behandlingsalternativ. En framgångsrik behandling kräver att den absorberade dosen till patienten kan ges med stor noggrannhet. Detta eftersom en liten avvikelse i absorberad dos kan påverka behandlingens resultat. Strålbehandling sker idag med avancerad teknik och utrustning där osäkerheterna i varje led i behandlingskedjan måste minimeras.



Ett led i förberedelserna är att beräkna den absorberade dosen till patienten. Detta görs idag med avancerade datorprogram, så kallade dosplaneringssystem. Noggrannheten i den beräknade dosen har vanligtvis studerats med experimentella mätningar. Experimentella data begränsas av vad som är praktiskt genomförbart och kan vara förenade med osäkerheter, som är relaterade till mätutrustningen. Behandlingsapparatens stabilitet i tiden påverkar också resultaten, då det kan ta dagar att samla in all den information som behövs.



I detta arbete har möjligheten och fördelarna med att använda en Monte Carlo-metod för att utvärdera noggrannheten i dosplaneringssystemens dos¬beräkning studerats. Monte Carlo är en sannolikhetsbaserad beräknings¬metod, som utgår från grundläggande fysikaliska egenskaper. En modell av en behandlingsapparat, en s.k. virtuell behandlingsapparat, har konstruerats i ett Monte Carlo-baserat datorprogram. Denna virtuella behandlingsapparat har använts för att bland annat generera information motsvarande den man kan mäta upp för kliniska behandlingsapparater. Den virtuella behandlings¬apparaten har lagts in i dosplaneringssystemet på samma sätt som kliniska behandlings¬apparater. Jämförelser mellan den virtuella behandlings¬apparaten (Monte Carlo-simuleringar) och dess motsvarighet i dos¬planerings¬systemet kan användas för att studera noggrannheten i den beräknade dos¬fördelningen i olika situationer. Denna virtuella behandlings¬apparat kan också användas för att studera hur väl dosplanerings¬sytemet kan beskriva de strålfält som genereras av behandlings¬apparaten.



Resultaten visar att konceptet med den virtuella behandlingsapparaten framgångsrikt kan användas för att studera noggrannheten i dosplanerings-systems dosberäkning. Fördelarna med detta koncept har också illustrerats i flera situationer, där motsvarande jämförelser baserade på mätningar är begränsade eller till och med omöjliga. Till exempel har noggrannheten i dosberäkningen för några vanliga patientbehandlingar studerats.



Konceptet med den virtuella behandlingsapparaten gör det möjligt att i detalj studera de modeller som beskriver strålfälten och den efterföljande beräkningen av dosfördelningen i patienten. Den virtuella behandlings-apparaten är därför ett värdefullt verktyg för både användare och tillverkare. (Less)
Abstract
This thesis presents a new verification concept, the virtual accelerator, for dose calculation algorithms used in treatment planning systems (TPSs) for external beam radiotherapy. The algorithm input data required to implement a treatment unit in the TPS are generated by Monte Carlo simulations as are the beam reference data needed for the subsequent evaluation of the dose calculation algorithm. The virtual accelerator and its corresponding unit in the TPS can thus be used for comprehensive verification of dose calculation algorithms in the TPS.



The virtual accelerator concept provides a new means of verifying dose calculation algorithms in TPSs. Properties that are difficult or even impossible to assess using... (More)
This thesis presents a new verification concept, the virtual accelerator, for dose calculation algorithms used in treatment planning systems (TPSs) for external beam radiotherapy. The algorithm input data required to implement a treatment unit in the TPS are generated by Monte Carlo simulations as are the beam reference data needed for the subsequent evaluation of the dose calculation algorithm. The virtual accelerator and its corresponding unit in the TPS can thus be used for comprehensive verification of dose calculation algorithms in the TPS.



The virtual accelerator concept provides a new means of verifying dose calculation algorithms in TPSs. Properties that are difficult or even impossible to assess using conventional measurements can be studied. Problems associated with conventional measurements, e.g., detector limitations and accelerator stability, can be circumvented. The flexibility of the virtual accelerator is high since additional beam reference data can be acquired without compromising the consistency of the data.



The feasibility of the virtual accelerator concept has been demonstrated by the successful implementation of a virtual photon accelerator and a virtual electron accelerator in commercial TPSs. The success of the implementations was determined by the ability of the dose calculation algorithms to reproduce the algorithm input data, and in most cases the agreement was within [+-]2%.



The advantages and usefulness of the virtual photon accelerator have been illustrated in a mediastinum and a hip-prostheses-like geometry. The ability of the virtual photon accelerator to generate both total dose and the primary and phantom-scattered components was used to study the performance of two dose calculation algorithms in the presence of metallic implants.



The virtual electron accelerator has been used to study the performance in homogeneous and inhomogeneous phantoms. Studies of the beam model and the handling of patient-specific inserts in the dose calculation algorithm were possible due to the ability of the virtual accelerator to separate the total dose into beam model components.



Another advantage of the virtual accelerator that has been utilized for both photons and electrons is the possibility of evaluating the accuracy achievable in anthropomorphic phantoms based on patient X-ray computed tomography data. This feature has been used for photon algorithms in the case of tangential breast treatment and for the electron algorithm in the cases of nose, parotid gland, thorax wall and spinal cord treatment. For the electron cases, an elliptical [gamma]-evaluation was performed in three dimensions. For the 0.02 Gy/2 mm criteria 92% of the volume receiving more than 0.85 Gy per 100 monitor units (MU) has [gamma]-values less than one in the worst case. The corresponding value for the volume receiving more than 0.10 Gy/100 MU is 98%. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Karlsson, Mikael, Inst. för strålningsvetenskaper Umeå universitet
organization
publishing date
type
Thesis
publication status
published
subject
keywords
radiologi, tomografi, medicinsk instrumentering, radiotherapy, dose calculation algorithm, verification, Monte Carlo calculation, electron beam, photon beam, Clinical physics, radiology, tomography, medical instrumentation, Klinisk fysiologi, treatment planning system
publisher
Medical Radiation Physics, Lund University
defense location
Onkologiska klinikens föreläsningssal, Universitetssjukhuset i Lund
defense date
2006-01-12 10:00
ISBN
91-628-6675-3
language
English
LU publication?
yes
id
0371ec9f-a28d-4d0b-8c86-650e8ee9e36f (old id 545995)
date added to LUP
2007-09-20 11:37:47
date last changed
2016-09-19 08:45:10
@phdthesis{0371ec9f-a28d-4d0b-8c86-650e8ee9e36f,
  abstract     = {This thesis presents a new verification concept, the virtual accelerator, for dose calculation algorithms used in treatment planning systems (TPSs) for external beam radiotherapy. The algorithm input data required to implement a treatment unit in the TPS are generated by Monte Carlo simulations as are the beam reference data needed for the subsequent evaluation of the dose calculation algorithm. The virtual accelerator and its corresponding unit in the TPS can thus be used for comprehensive verification of dose calculation algorithms in the TPS.<br/><br>
<br/><br>
The virtual accelerator concept provides a new means of verifying dose calculation algorithms in TPSs. Properties that are difficult or even impossible to assess using conventional measurements can be studied. Problems associated with conventional measurements, e.g., detector limitations and accelerator stability, can be circumvented. The flexibility of the virtual accelerator is high since additional beam reference data can be acquired without compromising the consistency of the data.<br/><br>
<br/><br>
The feasibility of the virtual accelerator concept has been demonstrated by the successful implementation of a virtual photon accelerator and a virtual electron accelerator in commercial TPSs. The success of the implementations was determined by the ability of the dose calculation algorithms to reproduce the algorithm input data, and in most cases the agreement was within [+-]2%.<br/><br>
<br/><br>
The advantages and usefulness of the virtual photon accelerator have been illustrated in a mediastinum and a hip-prostheses-like geometry. The ability of the virtual photon accelerator to generate both total dose and the primary and phantom-scattered components was used to study the performance of two dose calculation algorithms in the presence of metallic implants.<br/><br>
<br/><br>
The virtual electron accelerator has been used to study the performance in homogeneous and inhomogeneous phantoms. Studies of the beam model and the handling of patient-specific inserts in the dose calculation algorithm were possible due to the ability of the virtual accelerator to separate the total dose into beam model components.<br/><br>
<br/><br>
Another advantage of the virtual accelerator that has been utilized for both photons and electrons is the possibility of evaluating the accuracy achievable in anthropomorphic phantoms based on patient X-ray computed tomography data. This feature has been used for photon algorithms in the case of tangential breast treatment and for the electron algorithm in the cases of nose, parotid gland, thorax wall and spinal cord treatment. For the electron cases, an elliptical [gamma]-evaluation was performed in three dimensions. For the 0.02 Gy/2 mm criteria 92% of the volume receiving more than 0.85 Gy per 100 monitor units (MU) has [gamma]-values less than one in the worst case. The corresponding value for the volume receiving more than 0.10 Gy/100 MU is 98%.},
  author       = {Wieslander, Elinore},
  isbn         = {91-628-6675-3},
  keyword      = {radiologi,tomografi,medicinsk instrumentering,radiotherapy,dose calculation algorithm,verification,Monte Carlo calculation,electron beam,photon beam,Clinical physics,radiology,tomography,medical instrumentation,Klinisk fysiologi,treatment planning system},
  language     = {eng},
  publisher    = {Medical Radiation Physics, Lund University},
  school       = {Lund University},
  title        = {Verification of Dose Calculation Algorithms in Treatment Planning Systems for External Radiation Therapy: A Monte Carlo Approach},
  year         = {2006},
}