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3D Verification of Dynamic and Breathing Adapted Radiotherapy using Polymer Gel Dosimetry

Ceberg, Sofie LU (2010)
Abstract (Swedish)
Popular Abstract in Swedish

En cancerpatient kommer till sjukhuset för att genomgå en strålbehandlig. Sjukhusets personal tar bilder av patienten och identifierar tumörens placering och utbredning. Bilderna läggs in i ett datorprogram, som i sin tur simulerar en strålbehandling. Strålningsapparaten, dvs. linjäracceleratorn, har flera justerbara parametrar; strålfältets storlek, vinkeln på den infallande strålen och strålningens energi m fl. Genom att simulera olika inställningar på dessa parametrar kan behandlingen optimeras. Varje patient får på så sätt sin individuella behandlingsplan.

Innan patienten lägger sig på britsen inför bestrålningen verifieras behandlingen genom kontrollmätningar. Stråldosen, som mäts... (More)
Popular Abstract in Swedish

En cancerpatient kommer till sjukhuset för att genomgå en strålbehandlig. Sjukhusets personal tar bilder av patienten och identifierar tumörens placering och utbredning. Bilderna läggs in i ett datorprogram, som i sin tur simulerar en strålbehandling. Strålningsapparaten, dvs. linjäracceleratorn, har flera justerbara parametrar; strålfältets storlek, vinkeln på den infallande strålen och strålningens energi m fl. Genom att simulera olika inställningar på dessa parametrar kan behandlingen optimeras. Varje patient får på så sätt sin individuella behandlingsplan.

Innan patienten lägger sig på britsen inför bestrålningen verifieras behandlingen genom kontrollmätningar. Stråldosen, som mäts på den plats där patienten kommer att befinna sig, uppmäts med en detektor placerad i ett medium med samma densitet som mänsklig vävnad. Det finns flera olika typer av detektorer, men de allra flesta mäter dosen som ska ges till patienten i en punkt eller i ett plan. I denna studie har en geldosimeter utvecklats och använts för att mäta dosen under avancerade bestrålningsförhållanden. Gelen, vars egenskaper förändras vid bestrålning, är unik i sitt slag; dels kan dosen mätas i en hel volym, dels integreras dosen över tiden vilket möjliggör mätningar under dynamiska förhållanden.

Då tumören befinner sig i området kring bröstkorgen, t ex vid lung- eller bröstcancer, rör sig tumören pga. att patienten andas. För att undvika att tumören rör sig ut ur strålfältet används stora marginaler. En sådan åtgärd innebär att tumören alltid är i strålfältet trots patientens andningsrörelser, men också att mängden bestrålad frisk vävnad ökar. För att minska dosen till frisk vävnad, t ex till hjärta och lungor, har nya behandlingsmetoder tagits fram. Dessa andningsanpassade strål-behandlingar ställer antingen in linjäracceleratorn så att den strålar endast då patientens tumör är i strålfältet alternativt så följer strålen tumören i dess rörelse. På så sätt kan strålfältet anpassas till tumörens storlek och frisk omkringliggande vävnad bättre klarar sig undan strålningen.

Enligt Cancerfonden kommer var tredje svensk diagnostiseras med cancer under deras levnadstid. Ungefär hälften av dem får gå igenom strålbehandling. För att bemöta detta, har utvecklingen av avancerade bestrålningstekniker accelererat under de senaste tio åren. Idag kan patienter behandlas med tekniker där strålfältet roterat kring patienten samtidigt som strålfältet ändrar både storlek och intensitet, och detta samtidigt som hänsyn tas till patientens andningsrörelser.

Det som däremot inte utvecklats lika snabbt som behandlingsteknikerna är de detektorsystem med vilka vi kontrollmäter behandlingar med innan de ges till patienten.

I denna studie har flera gelsystem först undersökts för att se om de passar för att mäta dosen som levereras med dessa avancerade bestrålningstekniker. Efter olika tester togs den bäst lämpade gelen fram och dosmätningar av andningsanpassade rotationsbestrålningar har genomförts. Dessa mätresultat har jämförts med resultat uppmätta med andra system (fast gelen har varit den enda som mätt med hög upplösning i tre dimensioner), beräkningar och simuleringar. All data stämmer överrens, vilket visar att gelen är en bra detektor. Dessutom visar resultaten presenterade i denna avhandling på att stråldosen till patienter som ska få avancerad dynamisk strålbehandling faktiskt är enligt planerna. När nya tekniker ska introduceras i kliniken kan gel dosimetern bidra med unika mätdata för att säkerställa en korrekt behandling. (Less)
Abstract
Polymer gel dosimetry has been used since the 1990s, and several studies have shown that this detector system can be used for verification of static absorbed dose distributions in three dimensions (3D). Its unique properties, such as high resolution, normal tissue equivalence and independency of energy, field size and direction of the incident radiation, should also be advantageous for dosimetric verification of radiotherapy using today’s and tomorrow’s dynamic delivery techniques. However, unfavourable properties have also been reported, such as dose rate-, temperature-, oxygen contamination-, and cooling rate dependencies. It has been shown in this thesis that these shortcomings can be overcome by using a good practice strategy, and that... (More)
Polymer gel dosimetry has been used since the 1990s, and several studies have shown that this detector system can be used for verification of static absorbed dose distributions in three dimensions (3D). Its unique properties, such as high resolution, normal tissue equivalence and independency of energy, field size and direction of the incident radiation, should also be advantageous for dosimetric verification of radiotherapy using today’s and tomorrow’s dynamic delivery techniques. However, unfavourable properties have also been reported, such as dose rate-, temperature-, oxygen contamination-, and cooling rate dependencies. It has been shown in this thesis that these shortcomings can be overcome by using a good practice strategy, and that results can be obtained with an uncertainty comparable to other detector systems.

Modern dynamic treatment techniques such as for example breathing adapted radiotherapy have created a need for dosimetry during motion, which poses new challenges. The purpose of this thesis was to investigate the performance of polymer gel dosimetry in such situations. For comparison, measurements using 1D, 2D and quasi-3D detector systems, as well as Monte Carlo simulations, were used to validate the results obtained using gel dosimetry.

The absorbed dose integrating property during fractionated irradiation delivery was investigated for two different polymer gel systems. A fractionation dependency was observed, especially pronounced for one of the systems. This effect was further investigated using compartment modelling. The results indicated that the dose response was approximately independent of the fractionation scheme, provided that the total absorbed dose was delivered during the same total delivery time. Under respiratory-like motion no influence of the dose rate variation related to motion in and out of the beam was observed. Full 3D absorbed dose verifications were also carried out for advanced delivery techniques involving simultaneous beam intensity modulation and gantry rotation around the patient, so called volumetric modulated arc therapy (VMAT). Using both gel measurements and Monte Carlo simulations it was successfully demonstrated that the VMAT plan was both accurately calculated and delivered as planned. Additionally, the performance of a tumour-tracking system during VMAT delivery was investigated. The dosimetric measurements, obtained using both gel and a bi-planar diode array, verified the improved dose conformity when enabling the target tracking system.

In this thesis the unique 3D properties of gel dosimetry were fully utilized, and the known uncertainties were minimized in every step of the procedure. It was shown that polymer gel is a useful tool for relative 3D dosimetry in dynamic and breathing adaptive radiotherapy. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Montelius, Anders, Avd. för sjukhusfysik, Akademiska sjukhuset, 751 85 Uppsala
organization
publishing date
type
Thesis
publication status
published
subject
keywords
radiotherapy, 3D verification, polymer gel
pages
136 pages
publisher
Lund University (Media-Tryck)
defense location
Room 2005/2007, Entrance 44, Diagnostic Centre, Skåne University Hospital, Malmö
defense date
2010-11-05 13:15
ISBN
978-91-7473-041-8
language
English
LU publication?
yes
id
66131d3c-72ff-4847-a69c-a50eabc98a0d (old id 1691788)
date added to LUP
2010-10-12 08:11:39
date last changed
2016-09-19 08:45:13
@misc{66131d3c-72ff-4847-a69c-a50eabc98a0d,
  abstract     = {Polymer gel dosimetry has been used since the 1990s, and several studies have shown that this detector system can be used for verification of static absorbed dose distributions in three dimensions (3D). Its unique properties, such as high resolution, normal tissue equivalence and independency of energy, field size and direction of the incident radiation, should also be advantageous for dosimetric verification of radiotherapy using today’s and tomorrow’s dynamic delivery techniques. However, unfavourable properties have also been reported, such as dose rate-, temperature-, oxygen contamination-, and cooling rate dependencies. It has been shown in this thesis that these shortcomings can be overcome by using a good practice strategy, and that results can be obtained with an uncertainty comparable to other detector systems.<br/><br>
Modern dynamic treatment techniques such as for example breathing adapted radiotherapy have created a need for dosimetry during motion, which poses new challenges. The purpose of this thesis was to investigate the performance of polymer gel dosimetry in such situations. For comparison, measurements using 1D, 2D and quasi-3D detector systems, as well as Monte Carlo simulations, were used to validate the results obtained using gel dosimetry.<br/><br>
The absorbed dose integrating property during fractionated irradiation delivery was investigated for two different polymer gel systems. A fractionation dependency was observed, especially pronounced for one of the systems. This effect was further investigated using compartment modelling. The results indicated that the dose response was approximately independent of the fractionation scheme, provided that the total absorbed dose was delivered during the same total delivery time. Under respiratory-like motion no influence of the dose rate variation related to motion in and out of the beam was observed. Full 3D absorbed dose verifications were also carried out for advanced delivery techniques involving simultaneous beam intensity modulation and gantry rotation around the patient, so called volumetric modulated arc therapy (VMAT). Using both gel measurements and Monte Carlo simulations it was successfully demonstrated that the VMAT plan was both accurately calculated and delivered as planned. Additionally, the performance of a tumour-tracking system during VMAT delivery was investigated. The dosimetric measurements, obtained using both gel and a bi-planar diode array, verified the improved dose conformity when enabling the target tracking system. <br/><br>
In this thesis the unique 3D properties of gel dosimetry were fully utilized, and the known uncertainties were minimized in every step of the procedure. It was shown that polymer gel is a useful tool for relative 3D dosimetry in dynamic and breathing adaptive radiotherapy.},
  author       = {Ceberg, Sofie},
  isbn         = {978-91-7473-041-8},
  keyword      = {radiotherapy,3D verification,polymer gel},
  language     = {eng},
  pages        = {136},
  publisher    = {ARRAY(0x9c13b28)},
  title        = {3D Verification of Dynamic and Breathing Adapted Radiotherapy using Polymer Gel Dosimetry},
  year         = {2010},
}