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Photon Dose Calculations in a Fluence-Based Treatment Planning System: Data Processing, Implementation and Validation

Weber, Lars LU (2003)
Abstract
The accuracy of dose calculations for various aspects of a treatment planning system (TPS) using an energy fluence beam modelling has been evaluated. The investigated TPS uses a beam model, which separates the energy fluence into a number of sources in the treatment head. The energy fluence components are transported towards the patient and, together with the scatter generated in the patient, yield the total dose. The parameters in the model on which the calculations are based are derived from measured data.



Several steps must be performed before a TPS can be adopted for clinical use. The most basic step is to collect the data required for the dose calculation algorithm of the TPS, such as depth doses, dose profiles,... (More)
The accuracy of dose calculations for various aspects of a treatment planning system (TPS) using an energy fluence beam modelling has been evaluated. The investigated TPS uses a beam model, which separates the energy fluence into a number of sources in the treatment head. The energy fluence components are transported towards the patient and, together with the scatter generated in the patient, yield the total dose. The parameters in the model on which the calculations are based are derived from measured data.



Several steps must be performed before a TPS can be adopted for clinical use. The most basic step is to collect the data required for the dose calculation algorithm of the TPS, such as depth doses, dose profiles, output factors in air and in water, etc. In this work, an investigation has been made of different methods of measuring output factors in air. An investigation on the variability of the prescribed characterisation measurements among several users has also been conducted.



The treatment unit characterisation step involves taking the measured input data, stated by the TPS vendor, and converting these into the model parameters required by the TPS dose calculation model. TPS-calculated dose distributions for the standard characterisation fields have been evaluated and compared with the input dose measurements. This constitutes the basic quality control level for the individual beams. In clinical settings, a variety of accessories in terms of field shaping, compensators, wedges, etc, are commonly used. These different treatment scenarios have been evaluated in terms of the level of accuracy achievable. For a number of situations, e.g. beams in heterogeneous media, modulated and asymmetric beams and beams subject to different scattering volumes, the TPS dose calculations have been compared with measured and Monte Carlo simulated data. With the exception of dose calculations in the build up region and for some 60-degree wedge data, the dose calculations agree with measurements to within 3 % level. (Less)
Abstract (Swedish)
Popular Abstract in Swedish

Framgångsrik strålbehandling av cancerpatienter kräver att man kan bestämma den absorberade dosen i patienten med stor noggrannhet. Bara några enstaka procents avvikelse i absorberad dos kan ha betydelse för det kliniska resultatet avseende både tumörutläkning och normalvävnadsreaktioner.



För att beräkna den absorberade dosen i patienten används sofistikerade datorprogram, som tillsammans med hårdvaran i dagligt tal kallas ”dosplaneringssystem”. Moderna beräkningsmetoder är baserade på s.k. energideponeringskärnor som beskriver den absorberade dosen i vatten kring antingen en enda växelverkanspunkt (punktspridningsfunktion) eller alternativt längs en smal stråle. Med hjälp av... (More)
Popular Abstract in Swedish

Framgångsrik strålbehandling av cancerpatienter kräver att man kan bestämma den absorberade dosen i patienten med stor noggrannhet. Bara några enstaka procents avvikelse i absorberad dos kan ha betydelse för det kliniska resultatet avseende både tumörutläkning och normalvävnadsreaktioner.



För att beräkna den absorberade dosen i patienten används sofistikerade datorprogram, som tillsammans med hårdvaran i dagligt tal kallas ”dosplaneringssystem”. Moderna beräkningsmetoder är baserade på s.k. energideponeringskärnor som beskriver den absorberade dosen i vatten kring antingen en enda växelverkanspunkt (punktspridningsfunktion) eller alternativt längs en smal stråle. Med hjälp av dessa kärnor kan sedan den absorberade dosfördelningen i patienten beräknas.



I detta arbete har ett dosplaneringssystem, Helax-TMS, baserat på energideponeringskärnor, studerats. Systemet är det vanligast förekommande på svenska strålbehandlingsavdelningar. Inom ramen för arbetet har vi studerat den noggrannhet med vilken den absorberade dosfördelningen kan beräknas i olika situationer. Metoden som använts har varit att jämföra beräkningar i dosplaneringssystemet mot experimentella mätningar i vatten i identiska geometrier. Detta har fördelen att det är lätt att jämföra med dosplaneringsberäkningar samt med resultat från andra undersökningar eftersom detta är den gängse teknik som använts tidigare. Undantaget har varit fall där det är förknippat med experimentella svårigheter att mäta absorberad dos, exempelvis i områden motsvarande vävnader med täthet skild från mjukvävnad. I dessa fall har simuleringar med s.k. Monte Carlo teknik använts.



De områden som fokuserats på i denna studie har varit vanligt förekommande tekniker i samband med strålbehandling; öppna och kilade fält samt i samband med dessa; asymmetriska fält och geometrier med varierande vävnadstäthet. Olika behandlingstekniker som kompensationsfilter och kilfält genererade av kollimatorer i rörelse, s.k. dynamiska kilar, har också undersökts.



Resultaten visar att beräkningsmodellerna i Helax-TMS uppfyller allmänt accepterade krav i de flesta situationerna. För de flesta undersökta fallen har avvikelserna i absorberad dos varit inom intervallet ±3 %. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof De Wagter, Carlos, Dept of Radiotherapy and Nuclear Medicine, Ghent University, Belgium
organization
publishing date
type
Thesis
publication status
published
subject
keywords
radiobiologi, Nuclear medicine, Radiopharmaceutical technology, Radiofarmaceutisk teknik, Nukleärmedicin, radiobiology
pages
156 pages
defense location
Lund University Hospital, Onkologiska klinikens föreläsningssal
defense date
2003-10-17 10:15:00
ISBN
91-628-5580-8
language
English
LU publication?
yes
additional info
Article: Knöös T, Ahnesjö A, Nilsson P, Weber L 1995 Limitations of a pencil beam approach to photon dose calculations in lung tissue. Phys. Med. Biol. 40, 1411-1420 Article: Weber L, Ahnesjö A, Nilsson P, Saxner M, Knöös T 1996 Verification and implementation of dynamic wedge calculations in a treatment planning system based on a dose-to-energy-fluence formalism. Med. Phys. 23, 307-316 Article: Weber L, Nilsson P, Ahnesjö A 1997 Build-up cap materials for measurement of photon head-scatter factors. Phys. Med. Biol. 42, 1875-1886 Article: Weber L, Laursen F 2002 Dosimetric verification of modulated photon fields by means of compensators for a kernel model. Radiother. Oncol. 62, 87-93 Article: Weber L, Nilsson P 2002 Verification of dose calculations with a clinical treatment planning system based on a point kernel dose engine. J. Appl. Clin. Med. Phys. 3, 73-87 Article: Weber L, Ahnesjö A, Murman A, Saxner M, Thorslund I, Traneus E 2003 Beam modelling and verification of photon beam multi-source models. Manuscript
id
7bb5ed0f-b60c-4e6a-a30b-23a2e75e6f3d (old id 466204)
date added to LUP
2016-04-04 13:32:04
date last changed
2018-11-21 21:14:37
@phdthesis{7bb5ed0f-b60c-4e6a-a30b-23a2e75e6f3d,
  abstract     = {The accuracy of dose calculations for various aspects of a treatment planning system (TPS) using an energy fluence beam modelling has been evaluated. The investigated TPS uses a beam model, which separates the energy fluence into a number of sources in the treatment head. The energy fluence components are transported towards the patient and, together with the scatter generated in the patient, yield the total dose. The parameters in the model on which the calculations are based are derived from measured data.<br/><br>
<br/><br>
Several steps must be performed before a TPS can be adopted for clinical use. The most basic step is to collect the data required for the dose calculation algorithm of the TPS, such as depth doses, dose profiles, output factors in air and in water, etc. In this work, an investigation has been made of different methods of measuring output factors in air. An investigation on the variability of the prescribed characterisation measurements among several users has also been conducted.<br/><br>
<br/><br>
The treatment unit characterisation step involves taking the measured input data, stated by the TPS vendor, and converting these into the model parameters required by the TPS dose calculation model. TPS-calculated dose distributions for the standard characterisation fields have been evaluated and compared with the input dose measurements. This constitutes the basic quality control level for the individual beams. In clinical settings, a variety of accessories in terms of field shaping, compensators, wedges, etc, are commonly used. These different treatment scenarios have been evaluated in terms of the level of accuracy achievable. For a number of situations, e.g. beams in heterogeneous media, modulated and asymmetric beams and beams subject to different scattering volumes, the TPS dose calculations have been compared with measured and Monte Carlo simulated data. With the exception of dose calculations in the build up region and for some 60-degree wedge data, the dose calculations agree with measurements to within 3 % level.},
  author       = {Weber, Lars},
  isbn         = {91-628-5580-8},
  language     = {eng},
  school       = {Lund University},
  title        = {Photon Dose Calculations in a Fluence-Based Treatment Planning System: Data Processing, Implementation and Validation},
  url          = {https://lup.lub.lu.se/search/files/6143589/1693167.pdf},
  year         = {2003},
}