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Evaluation of respiratory gating – dose sparing and set-up

Edvardsson, Anneli (2012)
Medical Physics Programme
Abstract (Swedish)
Strålbehandling kan användas för att behandla olika cancerdiagnoser. Man vill då kunna rikta strålningen mot tumören medan så lite frisk vävnad som möjligt bestrålas. Olika studier visar att för patienter som behandlas med strålbehandling för cancer i vänster bröst är förekomsten av och dödligheten i olika hjärtsjukdomar högre än för de som behandlas med strålbehandling för cancer i höger bröst. Detta beror på den ökade stråldosen till hjärtat vid behandling av cancer i vänster bröst till följd av att hjärtat är placerat närmare vänster bröst än höger bröst. Ett sätt att minska stråldosen till hjärtat vid behandling av bröstcancer i vänster bröst är att använda andningsanpassad strålbehandling. Då får patienten andas in djupare än normalt... (More)
Strålbehandling kan användas för att behandla olika cancerdiagnoser. Man vill då kunna rikta strålningen mot tumören medan så lite frisk vävnad som möjligt bestrålas. Olika studier visar att för patienter som behandlas med strålbehandling för cancer i vänster bröst är förekomsten av och dödligheten i olika hjärtsjukdomar högre än för de som behandlas med strålbehandling för cancer i höger bröst. Detta beror på den ökade stråldosen till hjärtat vid behandling av cancer i vänster bröst till följd av att hjärtat är placerat närmare vänster bröst än höger bröst. Ett sätt att minska stråldosen till hjärtat vid behandling av bröstcancer i vänster bröst är att använda andningsanpassad strålbehandling. Då får patienten andas in djupare än normalt under behandlingen efter en röst som säger ”andas in” och ”andas ut”. Bestrålningen sker bara när patienten andats in. Då är avståndet mellan bröstet och hjärtat som störst och på så sätt kan stråldosen till hjärtat minskas. I denna studie visas att genom att behandla patienter med vänstersidig bröstcancer med andningsanpassad strålbehandling kan stråldosen till hjärtat minskas med 46 %, vilket resulterar i en minskning av sannolikheten att dö i hjärtsjukdomar för dessa kvinnor.

Innan strålbehandlingen får patienten göra en datortomografiundersökning, vilket är en form av röntgenundersökning som ger snittbilder av patienten i tre dimensioner. I dessa bilder planerar man sedan hur strålfälten ska gå för att få så bra fördelning av stråldosen till det område som ska behandlas samtidigt som man minimerar stråldosen till den friska vävnaden. Det är viktigt att patienten ligger likadant vid behandling som under datortomografin. Ligger patienten annorlunda leder det till att stråldosen inte hamnar på det område som det var tänkt vilket kan leda till bestrålning av riskorgan och att delar av behandlingsområdet inte får den stråldos det var tänkt. På grund av uppläggningsproceduren för de patienter som behandlas med andningsanpassad strålbehandling kommer de att ligga lite annorlunda vid varje behandling. Denna avvikelse i positioneringen är systematisk och påverkar samtliga tillfällen patienten behandlas och kan korrigeras med en korrektionsstrategi. Genom att använda en korrektionsstrategi kan man uppskatta den systematiska avvikelsen och korrigera för den. Om man inte använder någon korrektionsstrategi introducerar man stora systematiska positioneringsavvikelser genom att använda andningsanpassad strålbehandling, vilket påverkar dosfördelningen till behandlingsområdet och hjärtat. Det är därför viktigt att korrigera för dessa systematiska avvikelser. Denna studie visar att den allmänt vedertagna korrektionsstrategin inte är den optimala för de patienter som behandlas med andningsanpassad strålbehandling. En justering av denna korrektionsstrategi, som resulterar i en bättre positionering, föreslås istället användas för denna patientgrupp. (Less)
Abstract
Purpose: To evaluate the benefits of using respiratory gating for left-sided breast cancer in the form of dose-sparing and biological effects to the heart and to investigate the set-up deviations for patients treated with respiratory gating in order to find an optimal correction strategy for this group of patients.

Materials and methods: Nineteen patients treated with respiratory gating for left-sided breast cancer using the Real-time Position Management system (RPM, Varian Medical Systems, Inc., Palo Alto, CA) were retrospectively enrolled in this study. All patients had been treated with breast conserving surgery and no nodes were irradiated. Two CT-scans were performed for all patients treated with respiratory gating, one during deep... (More)
Purpose: To evaluate the benefits of using respiratory gating for left-sided breast cancer in the form of dose-sparing and biological effects to the heart and to investigate the set-up deviations for patients treated with respiratory gating in order to find an optimal correction strategy for this group of patients.

Materials and methods: Nineteen patients treated with respiratory gating for left-sided breast cancer using the Real-time Position Management system (RPM, Varian Medical Systems, Inc., Palo Alto, CA) were retrospectively enrolled in this study. All patients had been treated with breast conserving surgery and no nodes were irradiated. Two CT-scans were performed for all patients treated with respiratory gating, one during deep breathing and one during normal free breathing. Since the patients had been treated with respiratory gating, structure delineation and treatment plans had already been made in the gated CT image set. For evaluation of the dose sparing and radiobiological effect, structure delineation was carried out and individually optimized treatment plans were created also for conventional treatment. Comparable target coverage was the main criteria when creating the treatment plans. The relative seriality model was used to calculate the cardiac mortality probability for the two treatment techniques.
For evaluation of the set-up deviations, orthogonal kilovolt set-up images were acquired at every fraction for 18 patients treated with respiratory gating and 17 patients treated conventionally for comparison. In total, 659 images were acquired and manually matched with digitally reconstructed radiographs reconstructed from the CT image sets. Calculations of the set-up deviations were made both with no correction strategy applied and with the currently used correction strategy. The effect of the set-up deviation on the absorbed dose distribution was investigated by simulations in the treatment planning system (Eclipse version 10, Varian Medical Systems, Inc., Palo Alto, CA) and measurements with a biplanar diode array.

Results: The mean absorbed dose to the heart was decreased for all patients in this study using respiratory gating. The average mean absorbed dose to the heart was 2.6 Gy for conventional treatment and 1.4 Gy for respiratory gating, a reduction of 46 %. For the left anterior descending (LAD) coronary artery the average mean absorbed dose was 13.9 Gy for conventional treatment and 4.2 Gy for respiratory gating, a reduction of 70 %. These reductions are statistically significant (p<0.01). The average mean absorbed dose to the left lung was 5.8 Gy for both conventional treatment and respiratory gating. As a result of the dose sparing for the heart the cardiac mortality probability could be reduced from 0.58 % for conventional treatment to 0.05 % for respiratory gating.
An overall mean systematic deviation (moverall), calculated as the mean deviation for all patients and all treatment fractions, of 6.0 mm in the anterior direction and 8.1 mm in the cranial direction was present for the patients treated with respiratory gating if no correction strategy was applied. This set-up deviation results in increased absorbed dose to the organs at risk (OAR) and affects the absorbed dose distribution to the target. If the currently used correction strategy was applied to the deviations, moverall was reduced to 1.1 mm in the anterior direction and 3.3 mm in the cranial direction. moverall can be further reduced if the AML factor is excluded from the current correction strategy. If this was done, the moverall was 0.5 mm in the posterior direction and 1.0 mm in the cranial direction. No difference in the random set-up error was seen between the patients treated with conventional treatment and respiratory gating.

Conclusions: Significant dose-sparing to the heart and LAD can be achieved using respiratory gating without compromising the target coverage. As a result of this dose sparing, the cardiac mortality probability can be reduced. This was comparable with earlier results [10, 13]. If no correction strategy is used for respiratory gating large systematic set-up deviations will be present which would increase the absorbed dose to the OARs and affect the dose distribution to the PTV. By excluding the AML factor from the currently used NAL correction strategy, the set-up deviations for the patients treated with respiratory gating will be minimized. (Less)
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author
Edvardsson, Anneli
supervisor
organization
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
3327132
date added to LUP
2012-12-20 19:09:20
date last changed
2013-09-05 12:20:45
@misc{3327132,
  abstract     = {Purpose: To evaluate the benefits of using respiratory gating for left-sided breast cancer in the form of dose-sparing and biological effects to the heart and to investigate the set-up deviations for patients treated with respiratory gating in order to find an optimal correction strategy for this group of patients.

Materials and methods: Nineteen patients treated with respiratory gating for left-sided breast cancer using the Real-time Position Management system (RPM, Varian Medical Systems, Inc., Palo Alto, CA) were retrospectively enrolled in this study. All patients had been treated with breast conserving surgery and no nodes were irradiated. Two CT-scans were performed for all patients treated with respiratory gating, one during deep breathing and one during normal free breathing. Since the patients had been treated with respiratory gating, structure delineation and treatment plans had already been made in the gated CT image set. For evaluation of the dose sparing and radiobiological effect, structure delineation was carried out and individually optimized treatment plans were created also for conventional treatment. Comparable target coverage was the main criteria when creating the treatment plans. The relative seriality model was used to calculate the cardiac mortality probability for the two treatment techniques.
For evaluation of the set-up deviations, orthogonal kilovolt set-up images were acquired at every fraction for 18 patients treated with respiratory gating and 17 patients treated conventionally for comparison. In total, 659 images were acquired and manually matched with digitally reconstructed radiographs reconstructed from the CT image sets. Calculations of the set-up deviations were made both with no correction strategy applied and with the currently used correction strategy. The effect of the set-up deviation on the absorbed dose distribution was investigated by simulations in the treatment planning system (Eclipse version 10, Varian Medical Systems, Inc., Palo Alto, CA) and measurements with a biplanar diode array.

Results: The mean absorbed dose to the heart was decreased for all patients in this study using respiratory gating. The average mean absorbed dose to the heart was 2.6 Gy for conventional treatment and 1.4 Gy for respiratory gating, a reduction of 46 %. For the left anterior descending (LAD) coronary artery the average mean absorbed dose was 13.9 Gy for conventional treatment and 4.2 Gy for respiratory gating, a reduction of 70 %. These reductions are statistically significant (p<0.01). The average mean absorbed dose to the left lung was 5.8 Gy for both conventional treatment and respiratory gating. As a result of the dose sparing for the heart the cardiac mortality probability could be reduced from 0.58 % for conventional treatment to 0.05 % for respiratory gating.
An overall mean systematic deviation (moverall), calculated as the mean deviation for all patients and all treatment fractions, of 6.0 mm in the anterior direction and 8.1 mm in the cranial direction was present for the patients treated with respiratory gating if no correction strategy was applied. This set-up deviation results in increased absorbed dose to the organs at risk (OAR) and affects the absorbed dose distribution to the target. If the currently used correction strategy was applied to the deviations, moverall was reduced to 1.1 mm in the anterior direction and 3.3 mm in the cranial direction. moverall can be further reduced if the AML factor is excluded from the current correction strategy. If this was done, the moverall was 0.5 mm in the posterior direction and 1.0 mm in the cranial direction. No difference in the random set-up error was seen between the patients treated with conventional treatment and respiratory gating.

Conclusions: Significant dose-sparing to the heart and LAD can be achieved using respiratory gating without compromising the target coverage. As a result of this dose sparing, the cardiac mortality probability can be reduced. This was comparable with earlier results [10, 13]. If no correction strategy is used for respiratory gating large systematic set-up deviations will be present which would increase the absorbed dose to the OARs and affect the dose distribution to the PTV. By excluding the AML factor from the currently used NAL correction strategy, the set-up deviations for the patients treated with respiratory gating will be minimized.},
  author       = {Edvardsson, Anneli},
  language     = {eng},
  note         = {Student Paper},
  title        = {Evaluation of respiratory gating – dose sparing and set-up},
  year         = {2012},
}