Opportunities and limitations of multileaf collimator based intensity modulated proton therapy [Elektronische Ressource] / presented by Juliane Daartz

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Dissertationsubmitted to theCombined Faculties for the Natural Sciences and for Mathematicsof the Ruperto-Carola University of Heidelberg, Germanyfor the degree ofDoctor of Natural SciencesPresented byDiplom-Physiker: Juliane DaartzBorn in: RostockOral examination: May 4th 2011iiOpportunities and limitations of multileaf collimatorbased intensity modulated proton therapyReferees: Prof. Dr. Uwe OelfkeProf. Dr. Harald PaganettiivAbstractOpportunities and limitations of multileaf collimator based intensity modulatedproton therapyThe vast majority of proton therapy institutes employ passive scattering beamlines. Treatmentsare delivered by means of laterally and distally conformed homogeneous dose distributions foreach beam direction by utilizing spread-out Bragg peaks and custom milled hardware. Mostnewly built proton facilities rely upon scanned proton beams to provide intensity modulatedtherapy (IMPT), improvements in treatment planning and delivery work ow. This thesisinvestigates the bene ts of IMPT in xed proton therapy beamlines and describes aspects ofmultileaf collimator (MLC) based IMPT delivery. We show that IMPT has the potential toincrease the range of applications for xed proton therapy beamlines. A method for sequencingintensity modulated treatment plans into a set of segments is presented and evaluated based onresults obtained for a set of clinical situations.

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Published 01 January 2011
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Dissertation
submitted to the
Combined Faculties for the Natural Sciences and for Mathematics
of the Ruperto-Carola University of Heidelberg, Germany
for the degree of
Doctor of Natural Sciences
Presented by
Diplom-Physiker: Juliane Daartz
Born in: Rostock
Oral examination: May 4th 2011iiOpportunities and limitations of multileaf collimator
based intensity modulated proton therapy
Referees: Prof. Dr. Uwe Oelfke
Prof. Dr. Harald PaganettiivAbstract
Opportunities and limitations of multileaf collimator based intensity modulated
proton therapy
The vast majority of proton therapy institutes employ passive scattering beamlines. Treatments
are delivered by means of laterally and distally conformed homogeneous dose distributions for
each beam direction by utilizing spread-out Bragg peaks and custom milled hardware. Most
newly built proton facilities rely upon scanned proton beams to provide intensity modulated
therapy (IMPT), improvements in treatment planning and delivery work ow. This thesis
investigates the bene ts of IMPT in xed proton therapy beamlines and describes aspects of
multileaf collimator (MLC) based IMPT delivery. We show that IMPT has the potential to
increase the range of applications for xed proton therapy beamlines. A method for sequencing
intensity modulated treatment plans into a set of segments is presented and evaluated based on
results obtained for a set of clinical situations. The resulting numbers of segments made delivery
technically and logistically feasible. Neutron dose was found acceptable given a well optimized
beamline. The dosimetric properties of one speci c multileaf collimator were investigated
experimentally and compared to custom milled apertures. Small di erences were found, but
those are clinically insigni cant in the vast majority of clinical cases. Finally, an extensive
set of measurements for accurate determination of the peak dose as a function of eld size is
described.viZusammenfassung
Potenzial und Limitierungen von MLC basierter IMPT Anwendung
Die Mehrheit existierender Protonentherapiezentren nutzt passiv streuende Protonenstrahle-
nanlagen. Patientenbehandlungen basieren auf lateral und distal konformierten homogenen
Dosisverteilungen, die von jedem einzelnen Strahl durch spread-out Bragg Peaks und individu-
ell gefertigte Kollimatoren und Kompensatoren geliefert werden. Die Mehrheit der im Bau
be ndlichen Protonenzentren installiert Scanning Systeme auf Grund ihrer F ahigkeit zu inten-
sit atsmodulierter Protonentherapie (IMPT), sowie ihrer Vorteile im Bezug auf Vereinfachung
der Arbeitsabl aufe der Bestrahlungsplanung und -lieferung. Das Potenzial von IMPT speziell
im Bezug auf xe Protonenstrahlen liegt in einer Erweiterung derer Anwendungsm oglichkeiten.
Diese Arbeit schl agt Multileafkollimatoren (MLCs) fur die nachtr agliche Ausrustung existieren-
der passiv streuender Protonenstrahlanlagen zur Anwendung fur IMPT vor. Es wird eine
Methode zur Sequenzierung von Dosisverteilungen in Serien von Einzelsegmenten vorgestellt
und anhand einer Gruppe klinischer Anwendungen evaluiert. Basierend auf der resultierenden
Anzahl von Segmenten pro Strahlrichtung w are die praktische Umsetzung der vorgeschla-
genen Methode technisch und logistisch m oglich. Die Neutronendosis war akzeptabel mit
der Bedingung einer optimal abgestimmten Protonenstrahlanlage. Die dosimetrischen Eigen-
schaften eines speziellen MLCs wurden untersucht und mit den ublic h benutzten individuell
gefertigten Messingaperturen verglichen. Die gefunden Unterschiede sind klein und in der
Mehrheit klinischer Anwendungen vernachsl assigbar. Abschliessend wird die Relation zwischen
Strahlmaximumsdosis und Feldgr osse als wichtiger Teil der MLC basierten IMPT Dosislieferung
er ortert.viiiPreface
This PhD thesis was carried out at the Massachusetts General Hospital (MGH)
between November 2006 and December 2010. The work describes bene ts of IMPT for
xed passive scattering beamlines and an approach for MLC based IMPT delivery.
The work presented in Chapter 2.1 has in parts been funded by an MGH grant and will
be submitted for publication soon. Publications covering the contents of Chapters 3.1 and
3.2 can be found in [1] and [2], respectively. The topic of Chapter 3.2 has been addressed
in [3] but has since been much expanded with an improved methodology. Parts of single
chapters were presented at international conferences [4] [5] [6] [7]. The contribution for
PTCOG 48 in Heidelberg [7] was awarded the PTCOG prize for best Physics poster.2