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Implementation of MRI gel dosimetry in radiation therapy

Bäck, Sven LU (1998)
Abstract (Swedish)
Popular Abstract in Swedish

Gel-dosmätningar för kontroll av strålbehandling av cancertumörer



När en patient strålbehandlas avser man att bestråla sjuka områden i kroppen. Det är dock omöjligt att göra detta utan att därmed även till viss del stråla på omkringliggande organ och komplikationer kan då uppstå. För att minimera dessa bieffekter och optimera behandlingen används ofta en så kallad dosplanering. Med hjälp av datorer kan man simulera hur patienten ser ut och planera energi, riktning och utsträckning på strålningen som träffar kroppen. Datorn räknar sedan ut vilken absorberad dos olika organ och områden får vid vissa inställningar. Den absorberade dosen är samma sak som den energi som stannar i... (More)
Popular Abstract in Swedish

Gel-dosmätningar för kontroll av strålbehandling av cancertumörer



När en patient strålbehandlas avser man att bestråla sjuka områden i kroppen. Det är dock omöjligt att göra detta utan att därmed även till viss del stråla på omkringliggande organ och komplikationer kan då uppstå. För att minimera dessa bieffekter och optimera behandlingen används ofta en så kallad dosplanering. Med hjälp av datorer kan man simulera hur patienten ser ut och planera energi, riktning och utsträckning på strålningen som träffar kroppen. Datorn räknar sedan ut vilken absorberad dos olika organ och områden får vid vissa inställningar. Den absorberade dosen är samma sak som den energi som stannar i kroppen per viktenhet (joule per kilogram). Man vill alltså maximera den absorberade dosen i tumören och minimera den i normalvävnad.



Dosberäkningar kan vara svåra att kontrollera, särskilt i en patientlik situation. Man mäter ofta den absorberade dosen med olika detektorer i stora vattenbehållare. I denna avhandling har den nya tekniken med dosimetergel använts för att mäta den absorberade dosen i tre dimensioner. Gelen består av en gelningskomponent, som gelatin, och en strålkänslig lösning. När man strålar på gelen ändras den kemiska sammansättningen i proportion till dosen och genom att detektera denna förändring kan man alltså mäta dosen. I vårt fall använder man magnetisk resonans (MR) för att detektera förändringen och genom att man därmed får en bild av gelen i valfri riktning kan man läsa ut dosen inuti en volym.



I denna avhandling har en ny metod för direkt jämförelse av dosplanering och gel-dosmätningar utvecklats. Metoden har använts i kliniskt relevanta situationer. Avhandlingen visar på att dosimetergel och MR är en mycket lovande teknik som har förbättrats främst genom optimeringar av MR utvärderingen och användande av ny utrustning. (Less)
Abstract
Gel dosimetry was used together with magnetic resonance imaging (MRI) to measure three-dimensional absorbed dose distributions in radiation therapy. Two different dosimeters were studied: ferrous- and monomer gel, based on the principles of radiation-induced oxidation and polymerisation, respectively. Single clinical electron and photon beams were evaluated and gel dose distributions were mainly within 2% of conventional detector results. The ferrous-gel was also used for clinical proton beams. A decrease in signal per absorbed dose was found close to the end of the range of the protons (15-20%). This effect was explained as a linear energy transfer dependence, further supported with Monte Carlo simulations.



A method for... (More)
Gel dosimetry was used together with magnetic resonance imaging (MRI) to measure three-dimensional absorbed dose distributions in radiation therapy. Two different dosimeters were studied: ferrous- and monomer gel, based on the principles of radiation-induced oxidation and polymerisation, respectively. Single clinical electron and photon beams were evaluated and gel dose distributions were mainly within 2% of conventional detector results. The ferrous-gel was also used for clinical proton beams. A decrease in signal per absorbed dose was found close to the end of the range of the protons (15-20%). This effect was explained as a linear energy transfer dependence, further supported with Monte Carlo simulations.



A method for analysing and comparing data from treatment planning system (TPS) and gel measurements was developed. The method enables a new pixel by pixel evaluation, isodose comparison and dose volume histogram verification.



Two standard clinical radiation therapy procedures were examined using the developed TPS verification method. The treatment regimes included several beams of different radiation qualities. The TPS calculated data were in very good agreement with the dose distribution measured by the ferrous-gel. However, in a beam abutment region, larger dose difference was found. Beam adjustment errors and a minor TPS underestimation of the lateral scatter contribution outside the primary electron beam may explain the discrepancy.



The overall uncertainty in the ferrous-gel dose determination was considerably reduced using an optimised MRI acquisition protocol and a new MRI scanner. The relative dose uncertainty was found to be better than 3.3% for all dose levels (95% confidence level).



Using the method developed for comparing measured gel data with calculated treatment plans, the gel dosimetry method was proven to be a useful tool for radiation treatment planning verification. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Skretting, Arne, Radiumhospitalet, Oslo
organization
publishing date
type
Thesis
publication status
published
subject
keywords
oncology, Cytology, uncertainty, detector, dosimeter, ferrous ions, gel dosimetry, magnetic resonance imaging, monomers, polymerisation, proton, treatment planning verification, radiation therapy, cancerology, Cytologi, onkologi, cancer
pages
61 pages
publisher
Department of Radiation Physics, Lund university
defense location
Kirurgiska klinikens föreläsningssal, ingång 42, Universitetssjukhuset MAS, Malmö
defense date
1998-12-11 09:30
external identifiers
  • Other:ISRN: LUNFD6/NFRF- - 98/1009 - - SE
  • Other:ISRN: LUMEDW/MEMR - - 98/1009 - - SE
ISBN
91-628-3241-7
language
English
LU publication?
yes
id
d1c75097-66e7-44b1-9a6a-19628e7a55a1 (old id 39169)
date added to LUP
2007-08-01 11:31:02
date last changed
2016-09-19 08:45:04
@misc{d1c75097-66e7-44b1-9a6a-19628e7a55a1,
  abstract     = {Gel dosimetry was used together with magnetic resonance imaging (MRI) to measure three-dimensional absorbed dose distributions in radiation therapy. Two different dosimeters were studied: ferrous- and monomer gel, based on the principles of radiation-induced oxidation and polymerisation, respectively. Single clinical electron and photon beams were evaluated and gel dose distributions were mainly within 2% of conventional detector results. The ferrous-gel was also used for clinical proton beams. A decrease in signal per absorbed dose was found close to the end of the range of the protons (15-20%). This effect was explained as a linear energy transfer dependence, further supported with Monte Carlo simulations.<br/><br>
<br/><br>
A method for analysing and comparing data from treatment planning system (TPS) and gel measurements was developed. The method enables a new pixel by pixel evaluation, isodose comparison and dose volume histogram verification.<br/><br>
<br/><br>
Two standard clinical radiation therapy procedures were examined using the developed TPS verification method. The treatment regimes included several beams of different radiation qualities. The TPS calculated data were in very good agreement with the dose distribution measured by the ferrous-gel. However, in a beam abutment region, larger dose difference was found. Beam adjustment errors and a minor TPS underestimation of the lateral scatter contribution outside the primary electron beam may explain the discrepancy.<br/><br>
<br/><br>
The overall uncertainty in the ferrous-gel dose determination was considerably reduced using an optimised MRI acquisition protocol and a new MRI scanner. The relative dose uncertainty was found to be better than 3.3% for all dose levels (95% confidence level).<br/><br>
<br/><br>
Using the method developed for comparing measured gel data with calculated treatment plans, the gel dosimetry method was proven to be a useful tool for radiation treatment planning verification.},
  author       = {Bäck, Sven},
  isbn         = {91-628-3241-7},
  keyword      = {oncology,Cytology,uncertainty,detector,dosimeter,ferrous ions,gel dosimetry,magnetic resonance imaging,monomers,polymerisation,proton,treatment planning verification,radiation therapy,cancerology,Cytologi,onkologi,cancer},
  language     = {eng},
  pages        = {61},
  publisher    = {ARRAY(0x9e116a0)},
  title        = {Implementation of MRI gel dosimetry in radiation therapy},
  year         = {1998},
}