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Radiotherapy Gel Dosimetry: Development and Application of Normoxic Polymer Gels

Gustafsson, Helen LU (2004)
Abstract
In many radiotherapy applications, true three-dimensional dosimetry with good spatial resolution that can be achieved in a single measurement would be of great value. Polymer gel dosimetry fulfils many of the demands on such a system. In this study, methods to facilitate the implementation of gel dosimetry have been investigated. A new type of polymer gel, for which the response to absorbed dose is not negatively affected even if manufacturing is undertaken at normal levels of oxygen, called normoxic gel, was studied.



The concept of percentage dose resolution was introduced to enable optimization of gel compositions for use in relative dosimetry applications. This concept was applied to demonstrate the effects of varying... (More)
In many radiotherapy applications, true three-dimensional dosimetry with good spatial resolution that can be achieved in a single measurement would be of great value. Polymer gel dosimetry fulfils many of the demands on such a system. In this study, methods to facilitate the implementation of gel dosimetry have been investigated. A new type of polymer gel, for which the response to absorbed dose is not negatively affected even if manufacturing is undertaken at normal levels of oxygen, called normoxic gel, was studied.



The concept of percentage dose resolution was introduced to enable optimization of gel compositions for use in relative dosimetry applications. This concept was applied to demonstrate the effects of varying the gel composition on gel performance. Comparison between data obtained using magnetic resonance imaging and FT-Raman spectroscopy indicated that not all water protons attached to the polymer are accessible for exchange of magnetization with other proton groups.



Dose response characteristics were investigated for a polymer gel containing the antioxidant tetrakis(hydroxymethyl)phosphonium. The transversal relaxation time (R2) versus dose response increased with increasing amounts of monomer, while no systematic dependence on antioxidant concentration was observed. The investigated normoxic gel exhibited a dependence on temperature during irradiation, leading to differences in absolute R2 as well as deviations in relative depth dose curves. It was suggested that the deviation in R2 can be attributed to structural differences in the polymer matrix, caused by varying polymerisation temperature. A linear relationship between absorbed dose and optical attenuation coefficient was observed, which demonstrates the potential for evaluation using light transmission measurements. Low-density gel was manufactured by mixing normal density normoxic gel with Styrofoamä spheres. A linear correlation between R2 and dose was observed for doses up to 15 Gy.



Possible dose response dependence on linear energy transfer (LET) was investigated using proton beam absorbed dose measurements. An increased LET with depth was closely followed by a decrease in relative detector sensitivity, indicating that the response of this type of gel detector is dependent on LET. No significant effects were observed for LET < 2.5 keV/mm, indicating that the detector response would not be altered in the range of LET values expected for photons or electrons in a clinical range of energies.



The feasibility of using normoxic gel for intensity-modulated radiation therapy verification was investigated. Good agreement between treatment planning system calculations and measured data was obtained. For the planning target volume, the calculated and the measured mean relative dose was 96.8±2.5% (±1 SD) and 98.6±2.2%, respectively. The results indicated great potential for intensity-modulated radiation therapy verification using normoxic polymer gel. (Less)
Abstract (Swedish)
Popular Abstract in Swedish

Av de omkring 45 000 svenskar som årligen drabbas av cancer kommer ungefär hälften att botas, ofta med strålning som en del av behandlingen. Syftet med strålterapi är att oskadliggöra tumören, men utan att skada omgivande vävnad. Idealt vill man att stråldosen ska vara mycket hög i tumören, samtidigt som den är obefintlig i vävnaden runt omkring. Strålskador på frisk vävnad kan ge akuta biverkningar, till exempel i form av illamående eller hudirritation. Men strålning kan också ge upphov till skador som uppträder långt senare, som minskad fertilitet och till och med nya tumörer. Ny teknik både inom avbildning av tumörer, planering av strålbehandlingen och framför allt vid själva bestrålningen gör... (More)
Popular Abstract in Swedish

Av de omkring 45 000 svenskar som årligen drabbas av cancer kommer ungefär hälften att botas, ofta med strålning som en del av behandlingen. Syftet med strålterapi är att oskadliggöra tumören, men utan att skada omgivande vävnad. Idealt vill man att stråldosen ska vara mycket hög i tumören, samtidigt som den är obefintlig i vävnaden runt omkring. Strålskador på frisk vävnad kan ge akuta biverkningar, till exempel i form av illamående eller hudirritation. Men strålning kan också ge upphov till skador som uppträder långt senare, som minskad fertilitet och till och med nya tumörer. Ny teknik både inom avbildning av tumörer, planering av strålbehandlingen och framför allt vid själva bestrålningen gör att man har blivit bättre på att avgränsa strålningen till tumören. En naturlig följd är att öka dosen för att eliminera tumören. Men vad händer om något blir fel? Även till synes små störningar i tekniken kan få ödesdigra konsekvenser för patienten.



För att veta att allt blir som man tänkt sig utförs kontrollmätningar av behandlingarna. I vissa fall, t.ex. vid cancer i näsa/mun, mat- eller luftstrupe eller gynekologisk cancer, kan man placera en detektor i en hålighet nära tumören. I andra fall blir man tvungen att ”ersätta” patienten med en modell, till exempel en plastavgjutning av en del av människokroppen. I modellen borrar man ett antal hål för detektorer. Oavsett vilken av dessa metoder man använder får man ett mått på dosen i de punkter där man placerat detektorer, men man vet väldigt lite om fördelningen av stråldos i vävnaden utanför dessa punkter.



För kunna mäta dosen i en hel volym i stället för i en punkt behövs en modell som i sig är känslig för strålning. Geldetektorn kan fungera som en sådan. I en behållare av valfri form – till exempel en plastavgjutning av en kroppsdel – hälls en ofärgad gel. I gelen finns så kallade monomerer, en organisk molekyl med dubbelbindningar mellan två kolatomer. Vid bestrålning bryts dubbelbindningen, och monomererna länkar i stället ihop med varandra för att bilda långa kedjor, polymerer. De punkter där polymerisation har skett – det vill säga bestrålade punkter – kommer att synas som vita områden. De syns dels rent visuellt, dels på en så kallad magnet-resonansbild (MR-bild). MR-bilden är alltså en bild av hur dosfördelningen verkligen ser ut för just den här bestrålningen och ger svar på om strålningen ”träffat rätt”, det vill säga om dosfördelningen ser ut som det var tänkt.



För att geldetektorn skall komma att användas i praktiken är det viktigt att den är enkel att använda. En ny typ av gel, som är betydligt enklare att tillverka än de som använts tidigare har undersökts i den här avhandlingen. Bland annat har en gel med ungefär samma densitet som lungvävnad tillverkats genom att blanda gelen med små och väldigt lätta plastkulor. Vävnad med olika densitet sprider strålning på olika sätt, och tidigare har det inte funnits någon detektor som verkligen kan mäta hur mycket stråldos som ges till lungorna, t.ex. vid behandling av bröstcancer. Geldosimetri ger nya möjligheter för kontrollmätningar av strålbehandling, vilket i sin tur kommer att leda till förbättrade behandlingsresultat och en miskning i andelen biverkningar. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Associate Professor Ibbott, Geoffrey, MD Anderson Cancer Center, Houston, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Clinical physics, radiology, tomography, medical instrumentation, Klinisk fysiologi, tomografi, medicinsk instrumentering, Radiofarmaceutisk teknik, Radiopharmaceutical technology, proton, LET, FT Raman spectroscopy, MRI, normoxic gel, IMRT, 3D verification, polymer gel dosimetry, radiologi
pages
60 pages
publisher
Helen Gustavsson, Department of Medical Radiation Physics, Malmö University Hospital, SE-205 02 Malmö, Sweden,
defense location
rum 2005, plan 2, Diagnostiskt Centrum, ingång 44, UMAS
defense date
2004-04-30 10:15:00
ISBN
91-628-5962-5
language
English
LU publication?
yes
additional info
Article: I. Development and Optimization of a 2-Hydroxyethylacrylate MRI Polymer Gel Dosimeter.Helen Gustavsson, Sven Å.J. Bäck, Martin Lepage, Llew Rintoul and Clive Baldock. Phys. Med. Biol., 49: 227-241, 2004. Article: II. MAGIC-type Polymer Gel for Three-Dimensional Dosimetry: Intensity-Modulated Radiation Therapy Verification. Helen Gustavsson, Anna Karlsson, Pia Haraldsson, Per Engström, Sven Å.J. Bäck, Håkan Nyström and Lars E. Olsson. Med. Phys., 30(6): 1264-1271, 2003. Article: III. Dose Response Characteristics of a New Normoxic Polymer Gel Dosimeter. Helen Gustavsson, Anna Karlsson, Sven Å.J. Bäck and Lars E. Olsson. Manuscript Article: IV. LET Dependence of a Normoxic Polymer Gel Dosimeter Investigated using Proton Beam Absorbed Dose Measurements. Helen Gustavsson, Sven Å.J. Bäck, Joakim Medin, Erik Grusell and Lars E. Olsson. Submitted to Phys. Med. Biol.
id
af048190-c7aa-4965-a174-75f6218b1916 (old id 466928)
date added to LUP
2016-04-04 10:09:34
date last changed
2018-11-21 20:57:07
@phdthesis{af048190-c7aa-4965-a174-75f6218b1916,
  abstract     = {{In many radiotherapy applications, true three-dimensional dosimetry with good spatial resolution that can be achieved in a single measurement would be of great value. Polymer gel dosimetry fulfils many of the demands on such a system. In this study, methods to facilitate the implementation of gel dosimetry have been investigated. A new type of polymer gel, for which the response to absorbed dose is not negatively affected even if manufacturing is undertaken at normal levels of oxygen, called normoxic gel, was studied.<br/><br>
<br/><br>
The concept of percentage dose resolution was introduced to enable optimization of gel compositions for use in relative dosimetry applications. This concept was applied to demonstrate the effects of varying the gel composition on gel performance. Comparison between data obtained using magnetic resonance imaging and FT-Raman spectroscopy indicated that not all water protons attached to the polymer are accessible for exchange of magnetization with other proton groups.<br/><br>
<br/><br>
Dose response characteristics were investigated for a polymer gel containing the antioxidant tetrakis(hydroxymethyl)phosphonium. The transversal relaxation time (R2) versus dose response increased with increasing amounts of monomer, while no systematic dependence on antioxidant concentration was observed. The investigated normoxic gel exhibited a dependence on temperature during irradiation, leading to differences in absolute R2 as well as deviations in relative depth dose curves. It was suggested that the deviation in R2 can be attributed to structural differences in the polymer matrix, caused by varying polymerisation temperature. A linear relationship between absorbed dose and optical attenuation coefficient was observed, which demonstrates the potential for evaluation using light transmission measurements. Low-density gel was manufactured by mixing normal density normoxic gel with Styrofoamä spheres. A linear correlation between R2 and dose was observed for doses up to 15 Gy.<br/><br>
<br/><br>
Possible dose response dependence on linear energy transfer (LET) was investigated using proton beam absorbed dose measurements. An increased LET with depth was closely followed by a decrease in relative detector sensitivity, indicating that the response of this type of gel detector is dependent on LET. No significant effects were observed for LET &lt; 2.5 keV/mm, indicating that the detector response would not be altered in the range of LET values expected for photons or electrons in a clinical range of energies.<br/><br>
<br/><br>
The feasibility of using normoxic gel for intensity-modulated radiation therapy verification was investigated. Good agreement between treatment planning system calculations and measured data was obtained. For the planning target volume, the calculated and the measured mean relative dose was 96.8±2.5% (±1 SD) and 98.6±2.2%, respectively. The results indicated great potential for intensity-modulated radiation therapy verification using normoxic polymer gel.}},
  author       = {{Gustafsson, Helen}},
  isbn         = {{91-628-5962-5}},
  keywords     = {{Clinical physics; radiology; tomography; medical instrumentation; Klinisk fysiologi; tomografi; medicinsk instrumentering; Radiofarmaceutisk teknik; Radiopharmaceutical technology; proton; LET; FT Raman spectroscopy; MRI; normoxic gel; IMRT; 3D verification; polymer gel dosimetry; radiologi}},
  language     = {{eng}},
  publisher    = {{Helen Gustavsson, Department of Medical Radiation Physics, Malmö University Hospital, SE-205 02 Malmö, Sweden,}},
  school       = {{Lund University}},
  title        = {{Radiotherapy Gel Dosimetry: Development and Application of Normoxic Polymer Gels}},
  year         = {{2004}},
}