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Surface guided radiotherapy for high precision treatments of brain metastases

Konradsson, Elise (2018) MSFT01 20181
Medical Physics Programme
Abstract
Purpose/Background
High accuracy treatment techniques such as stereotactic radiotherapy (SRT) requires precise patient positioning prior to and during treatment. The Catalyst™ is an optical surface scanning (OSS) system that has been utilized for patient positioning and real time monitoring during radiotherapy. The company behind the system recently released a novel algorithm for calculating the isocenter shift, specialized for SRT treatments. The aim of this master thesis was to evaluate if the OSS system with the novel SRT algorithm provides suffcient accuracy for positioning and real time monitoring of SRT treatments.

Material and methods
A study was performed using a RANDO Alderson phantom (Alderson et al. (1962) [1]), an... (More)
Purpose/Background
High accuracy treatment techniques such as stereotactic radiotherapy (SRT) requires precise patient positioning prior to and during treatment. The Catalyst™ is an optical surface scanning (OSS) system that has been utilized for patient positioning and real time monitoring during radiotherapy. The company behind the system recently released a novel algorithm for calculating the isocenter shift, specialized for SRT treatments. The aim of this master thesis was to evaluate if the OSS system with the novel SRT algorithm provides suffcient accuracy for positioning and real time monitoring of SRT treatments.

Material and methods
A study was performed using a RANDO Alderson phantom (Alderson et al. (1962) [1]), an open-face mask and the OSS system. For positioning at couch angle 0°, the agreement between the isocenter shift calculated by the OSS system and the isocenter shift suggested after imageverification with Cone-Beam Computed Tomography (CBCT) was evaluated. For non-coplanar treatments the accuracy of positioning and monitoring was evaluated by isolating the couch offset and the uncertainties in the OSS systems calculation of the isocenter shift. Furthermore, an evaluation of the dosimetric effect of patient positioning uncertainties in clinical non-coplanar SRT treatment plans was carried out.

Results
The agreement between the OSS system and the CBCT system for different tumor positions were within 0.5 mm in the longitudinal direction and within 0.3 mm in the vertical and lateral directions. For all rotational directions the agreement were within 0.9°. The OSS system indicated that when rotating the couch used in this study, the position of the phantom relative to the treatment isocenter was shifted up to 1.2 mm. The couch rotation offset were larger for larger couch angles, although within 0.6 mm. The OSS system's uncertainty in the calculation of the isocenter position was within 0.5 mm. Within this study, the worst-case scenario for current work ow entails a risk of a 21.6% decrease of V(95%). However, with the OSS system as a complement for positioning the worst-case scenario would instead be limited to a 11.1% decrease of V(95%).

Conclusions
The OSS system evaluated within this thesis has the potential to improve patient positioning for SRT treatments. It has been concluded that the OSS system with the novel SRT algorithm show excellent agreement with the CBCT system and has the ability to validate the position of a phantom with 0.5 mm accuracy, at all couch angles. When tracking the surface, the only additional uncertainties are the motion and deformation of the surface. Thus, the OSS system has no problem monitoring the phantom position. However, the system must be further tested on volunteers and patients before clinical implementation, for which there will be some surface motion and deformation. This master thesis is the first step towards commissioning of the OSS system and open-face masks for SRT treatments in the clinic. (Less)
Popular Abstract (Swedish)
Antalet cancerpatienter i Sverige ökar. Varje år diagnostiseras över 60 000 fall. Den vanligaste formen av cancer i hjärnan är hjärnmetastaser som uppstår då cancerceller sprider sig från den primära tumören till hjärnan. Patienter med hjärnmetastaser har en övergripande dålig prognos och bidrar signifikant till antalet cancerdödsfall. Patienterna behandlas oftast med kirurgi, strålbehandling eller en kombination av dessa två metoder.

Målet vid strålbehandling är att bestråla hela tumörområdet och samtidigt skona den friska omkringliggande vävnaden i så hög grad som möjligt. En teknik inom strålbehandling som ofta används vid hjärnmetastaser är stereotaktisk strålbehandling (SRT) vilket innebär att man behandlar små volymer med mycket... (More)
Antalet cancerpatienter i Sverige ökar. Varje år diagnostiseras över 60 000 fall. Den vanligaste formen av cancer i hjärnan är hjärnmetastaser som uppstår då cancerceller sprider sig från den primära tumören till hjärnan. Patienter med hjärnmetastaser har en övergripande dålig prognos och bidrar signifikant till antalet cancerdödsfall. Patienterna behandlas oftast med kirurgi, strålbehandling eller en kombination av dessa två metoder.

Målet vid strålbehandling är att bestråla hela tumörområdet och samtidigt skona den friska omkringliggande vävnaden i så hög grad som möjligt. En teknik inom strålbehandling som ofta används vid hjärnmetastaser är stereotaktisk strålbehandling (SRT) vilket innebär att man behandlar små volymer med mycket höga stråldoser i få antal fraktioner. Vid denna typ av avancerade behandlingar ställs extra höga krav på noggrann positionering av patienten på behandlingsbritsen.

För att säkerställa patientpositionen krävs att patienterna fixeras. För patienter som får strålbehandling mot hjärnan används konventionellt heltäckande plastmasker som gjuts efter patientens huvud och fästs i britsen. Maskens syfte är att reproducera uppläggningen vid varje behandlingstillfälle, och samtidigt begränsa rörelser under behandlingen. Före behandling tas en verifikationsbild (3D-röntgenbild) för att kontrollera att patienten ligger rätt. Detta arbetsflöde har dock en del svagheter. Eftersom patientpositioneringen endast verifieras före behandlingen finns det inget sätt att kontrollera om patienten rör sig under tiden då strålningen levereras. Under behandlingen kan patienten röra på sig utan att detta noteras av behandlingspersonalen. Dessutom, vid SRT-behandlingar med olika britsvinklar, kan positionen endast verifieras i britsvinkel 0°. Efter verifikation och korrektion av patientposition antas att patienten är korrekt positionerad i efterföljande britsvinklar. Ytterligare en nackdel är att patienterna ofta upplever att de heltäckande maskerna är obekväma och obehagliga. Det finns alltså ett kliniskt behov av att förbättra arbetsflödet vid stereotaktiska behandlingar av hjärnan.

I detta examensarbete utvärderades potentialen att förbättra patientpositioneringen vid SRT-behandlingar genom att reducera fixeringen och använda öppna masker i kombination med ett oberoende optiskt ytskanningssystem (OSS-system). OSS-systemet skannar patientens yta och beräknar patientens position i rummet. Företaget bakom OSS-systemet som används i detta arbete har nyligen släppt en ny algoritm som är specialiserad för SRT-behandlingar. I studien utvärderades bland annat noggrannhet i positionering för olika britsvinklar med hjälp av ett patientlikt fantom.

Arbetets resultat visar på många fördelar med en klinisk implementering av öppna masker och OSS-systemet för SRT-behandlingar. OSS-systemet kan validera patientpositionen i britsvinkel 0° med samma noggrannhet som nuvarande "gyllene standard" för patientpositionering, och dessutom med god noggrannhet för diverse britsvinklar. Systemet kan även övervaka patientens position i realtid under behandlingen vilket resulterar i säkrare och noggrannare SRT-behandlingar. (Less)
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author
Konradsson, Elise
supervisor
organization
course
MSFT01 20181
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8958985
date added to LUP
2018-09-18 09:05:41
date last changed
2018-10-12 13:39:50
@misc{8958985,
  abstract     = {Purpose/Background
High accuracy treatment techniques such as stereotactic radiotherapy (SRT) requires precise patient positioning prior to and during treatment. The Catalyst™ is an optical surface scanning (OSS) system that has been utilized for patient positioning and real time monitoring during radiotherapy. The company behind the system recently released a novel algorithm for calculating the isocenter shift, specialized for SRT treatments. The aim of this master thesis was to evaluate if the OSS system with the novel SRT algorithm provides suffcient accuracy for positioning and real time monitoring of SRT treatments.

Material and methods
A study was performed using a RANDO Alderson phantom (Alderson et al. (1962) [1]), an open-face mask and the OSS system. For positioning at couch angle 0°, the agreement between the isocenter shift calculated by the OSS system and the isocenter shift suggested after imageverification with Cone-Beam Computed Tomography (CBCT) was evaluated. For non-coplanar treatments the accuracy of positioning and monitoring was evaluated by isolating the couch offset and the uncertainties in the OSS systems calculation of the isocenter shift. Furthermore, an evaluation of the dosimetric effect of patient positioning uncertainties in clinical non-coplanar SRT treatment plans was carried out.

Results
The agreement between the OSS system and the CBCT system for different tumor positions were within 0.5 mm in the longitudinal direction and within 0.3 mm in the vertical and lateral directions. For all rotational directions the agreement were within 0.9°. The OSS system indicated that when rotating the couch used in this study, the position of the phantom relative to the treatment isocenter was shifted up to 1.2 mm. The couch rotation offset were larger for larger couch angles, although within 0.6 mm. The OSS system's uncertainty in the calculation of the isocenter position was within 0.5 mm. Within this study, the worst-case scenario for current work ow entails a risk of a 21.6% decrease of V(95%). However, with the OSS system as a complement for positioning the worst-case scenario would instead be limited to a 11.1% decrease of V(95%).

Conclusions
The OSS system evaluated within this thesis has the potential to improve patient positioning for SRT treatments. It has been concluded that the OSS system with the novel SRT algorithm show excellent agreement with the CBCT system and has the ability to validate the position of a phantom with 0.5 mm accuracy, at all couch angles. When tracking the surface, the only additional uncertainties are the motion and deformation of the surface. Thus, the OSS system has no problem monitoring the phantom position. However, the system must be further tested on volunteers and patients before clinical implementation, for which there will be some surface motion and deformation. This master thesis is the first step towards commissioning of the OSS system and open-face masks for SRT treatments in the clinic.},
  author       = {Konradsson, Elise},
  language     = {eng},
  note         = {Student Paper},
  title        = {Surface guided radiotherapy for high precision treatments of brain metastases},
  year         = {2018},
}