Independent Monitor Unit Calculations in Intensity Modulated Radiotherapy
(2007)Medical Physics Programme
- Abstract
- Independent dose calculations in radiotherapy are important as they help assure that the dose given to the patient is the same as the prescribed. The current version of software Radiation Verification Programme, RVP, does not take into account the effects that occur when a beam from a linear accelerator is moved off-axis. The aim with this project was to find a model for these effects, fit the parameters in the model with data from measurements and then to test the model in clinically relevant situations. Preferably the model should be easily incorporated into the software. Three variable parameters were used for the model; the slope, which is the proportional factor with which the dose increases with the distance, the width which affects... (More)
- Independent dose calculations in radiotherapy are important as they help assure that the dose given to the patient is the same as the prescribed. The current version of software Radiation Verification Programme, RVP, does not take into account the effects that occur when a beam from a linear accelerator is moved off-axis. The aim with this project was to find a model for these effects, fit the parameters in the model with data from measurements and then to test the model in clinically relevant situations. Preferably the model should be easily incorporated into the software. Three variable parameters were used for the model; the slope, which is the proportional factor with which the dose increases with the distance, the width which affects the penumbra, and the leakage, which is the transmission through the field shielding. To fit the parameters for the model, measurements of fields placed off-axis were performed. This was done for two different linear accelerators; Varian Clinac 2100 and Elekta Precise, and one energy for both accelerators; 6 MV (Mega Voltage). Profiles were measured as to get the fields’ entire spread. The data gained from these measurements were used to fit the model’s parameters. The fitted model was first tested on profiles and then on IMRT fields in two dimensions. The model was simple, both in terms of measurements and implementation and showed good agreement for profiles measured through the central axis. The second step was to test the model for IMRT fields. The 2D arrays were compared using gamma comparison and with a 5 %/5 mm demand the pass rate was very high. Only a small number of fields were used and therefore no statistical certainty is guaranteed, but if further testing get similar results, the model can be used in clinical cases for dose calculations for beams off-axis and IMRT fields. (Less)
- Abstract (Swedish)
- Varje år får cirka 50 000 svenskar diagnosen cancer. Mot detta är strålbehandling en vanlig behandlingsmetod och det uppskattas att cirka en tredjedel av alla som får cancer någon gång under sin behandling får strålbehandling.
En viktig sak inom strålbehandling är att patienten får den dos som läkaren har ordinerat. Detta är en så vital detalj inom strålbehandling att SSI, Statens Strålskyddsinstitut, har reglerat att dosen ska beräknas med två oberoende metoder innan behandling. Detta för att kunna säkerställa patientdosen.
Vid de båda universitetssjukhusen i Lund och Malmö har man tidigare utvecklat ett datorprogram som gör just detta, beräknar dosen med en oberoende metod. Detta program är fortfarande under utveckling, men... (More) - Varje år får cirka 50 000 svenskar diagnosen cancer. Mot detta är strålbehandling en vanlig behandlingsmetod och det uppskattas att cirka en tredjedel av alla som får cancer någon gång under sin behandling får strålbehandling.
En viktig sak inom strålbehandling är att patienten får den dos som läkaren har ordinerat. Detta är en så vital detalj inom strålbehandling att SSI, Statens Strålskyddsinstitut, har reglerat att dosen ska beräknas med två oberoende metoder innan behandling. Detta för att kunna säkerställa patientdosen.
Vid de båda universitetssjukhusen i Lund och Malmö har man tidigare utvecklat ett datorprogram som gör just detta, beräknar dosen med en oberoende metod. Detta program är fortfarande under utveckling, men används också kliniskt för beräkningar av doser vid enkla behandlingar.
Ett strålfält från en linjäraccelerator är inte homogent. Mitt i fältet, i isocenter, är den plats som alla data finns om. Eftersom fältet ändras blir dosen olika vid olika platser i fältet och det finns ingen generell metod för hur dosen ändras, detta är individuellt för alla linjäracceleratorer.
I detta projekt har en metod utvecklas som tar hänsyn till dessa förändringar på ett enkelt sätt. På så sätt kan man verkligen vara säker på att datorprogrammet räknar rätt och på så sätt kan man verifiera att patienten får rätt stråldos vid sin strålbehandling.
Modellen testades först för profiler genom strålfältet vilket visade sig ge en bra överrensstämmelse. Vidare testades modellen också för fält som används vid patientbehandlingar. Dessa fält är intensitetsmodulerade vilket innebär att många fält placeras ovanpå varandra. I och med detta skulle ett litet fel kunna fortplantas och ge ett stort totalt fel. Då modellen testades gavs inga stora avvikelser. Emellertid testades inte tillräckligt många fält för att kunna garantera statistik säkerhet, men visar ytterligare test på samma resultat skulle modellen kunna användas i kliniken för beräkningar av stråldoser till patienter. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/2157010
- author
- Ramsing, Helena
- supervisor
-
- Sven Bäck LU
- Peter Björk LU
- Stefan Johnsson LU
- Crister Ceberg LU
- organization
- year
- 2007
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Strålterapi
- language
- English
- id
- 2157010
- date added to LUP
- 2011-09-13 13:01:26
- date last changed
- 2011-12-08 10:49:12
@misc{2157010,
abstract = {{Independent dose calculations in radiotherapy are important as they help assure that the dose given to the patient is the same as the prescribed. The current version of software Radiation Verification Programme, RVP, does not take into account the effects that occur when a beam from a linear accelerator is moved off-axis. The aim with this project was to find a model for these effects, fit the parameters in the model with data from measurements and then to test the model in clinically relevant situations. Preferably the model should be easily incorporated into the software. Three variable parameters were used for the model; the slope, which is the proportional factor with which the dose increases with the distance, the width which affects the penumbra, and the leakage, which is the transmission through the field shielding. To fit the parameters for the model, measurements of fields placed off-axis were performed. This was done for two different linear accelerators; Varian Clinac 2100 and Elekta Precise, and one energy for both accelerators; 6 MV (Mega Voltage). Profiles were measured as to get the fields’ entire spread. The data gained from these measurements were used to fit the model’s parameters. The fitted model was first tested on profiles and then on IMRT fields in two dimensions. The model was simple, both in terms of measurements and implementation and showed good agreement for profiles measured through the central axis. The second step was to test the model for IMRT fields. The 2D arrays were compared using gamma comparison and with a 5 %/5 mm demand the pass rate was very high. Only a small number of fields were used and therefore no statistical certainty is guaranteed, but if further testing get similar results, the model can be used in clinical cases for dose calculations for beams off-axis and IMRT fields.}},
author = {{Ramsing, Helena}},
language = {{eng}},
note = {{Student Paper}},
title = {{Independent Monitor Unit Calculations in Intensity Modulated Radiotherapy}},
year = {{2007}},
}