Dosimetric characteristic of an amorphous silicon based electronic portal imaging device and verification of intensity modulated radiation therapy plans

Zsfassung in dt. SpracheIntensitätsmodulierte Strahlentherapie (IMRT) gehört zu den fortschrittlichsten Techniken, die heute im Bereich der Teletherapie existieren. Die Technik ermöglicht es die im Körper platzierte Dosis in drei Dimensionen an die Form des Tumors anzupassen. So kann im Vergleich zu konventioneller und konformaler Strahlentherapie im Tumor eine höhere Dosis platziert werden, während umliegendes, gesundes Gewebe besser geschont werden kann.Da IMRT Felder sehr komplex sein können, werden im Verfikationsprozess hohe Anforderungen an räumliche Auflösung des Messgeräts gestellt. Mit einem, auf amorphen Silizium basierenden, Electronic Portal Imaging device (EPID), wie dem Varian aS1000, können die komplexen Dosisverteilungen die bei der Planung von IMRT Plänen entstehen, in Echtzeit mit Hilfe eines Computerprogramms aufgenommen werden.Ziel dieser Diplomarbeit war es, ein Varian aS1000 im Landesklinikum Wiener Neustadt zur Verifikation von IMRT Plänen in den Arbeitsablauf zu integrieren. Dazu musste das Gerät für Absolutdosismessungen kalibriert werden um danach verschiedene dosimetrische Eigenschaften, wie die Linearität, die Abhängigkeit der Feldgröße vom Fokus-Detektor-Abstand (SDD), Ghosting und Tiefendosiskurven messen zu können. Dann wurde das Gerät abmontiert und Schnittbilder in einem Computertomgraphen (CT) angefertigt. Auf diesen CT Bildern basierend wurden eigens dafür entwickelte Testmatrizen geplant und ausgelesen, die dann mittels der Gamma Evaluation mit den gemessenen Dosisverteilungen verglichen wurden.Letztendlich wurden die Pläne der sechs Patienten, die bisher am LK Wiener Neustadt mittels IMRT bestrahlt wurden, mit dem EPID erfolgreich verifiziert.Intensity modulated radiation therapy (IMRT) is today among the most advanced techniques in radiation therapy. This technique enables the dose distribution in the body to be modelled very accurately in three dimensions. Compared to conventional and conformal radiation therapy it allows to deposit more dose in the target volume and reduce the dose in healthy tissue around the tumour. Due to complex fields in IMRT it is necessary to verify the fields of the IMRT plans at a high resolution. With an amorphous electronic portal imaging device, like the aS1000 by Varian, it is possible to measure dose distributions produced by IMRT fields in real time.Goal of this thesis was to introduce a Varian aS1000 EPID for verification of IMRT plans into the department of oncology at the Landesklinikum Wiener Neustadt. Therefore the device had to be calibrated for absolute dosimetric measruements. After that, dosimetric properties of the EPID like linearity, fieldsize dependence on source to dedector distance (SDD), ghosting and depth dose curves were measured.Then the EPID was dismounted and computerized tomography (CT) images of the device were produced. Based on these images a set of test patterns were planned in Varian Eclipse and compared to the measured dose distributions with the gamma evaluation method.Finally the plans of all six patients, treated at the Landesklinikum Wiener Neustadt with IMRT, were successfully verified with the EPID.10

A Shielding Concept for the MedAustron Facility

MedAustron is a synchrotron based accelerator facility for cancer therapy and research in Wiener Neustadt, 50 km south of Vienna. The facility will provide protons up to kinetic energies of 250 MeV and carbon ions up to 400 MeV/n for ion beam therapy. Additionally, protons up to 800 MeV kinetic energy will be used in a dedicated room for non-clinical research. In order to obtain a shielding concept for this facility a detailed geometry of the accelerator facility was implemented into the Monte-Carlo code FLUKA and shielding simulations were performed. In the course of these simulations the contributions of different particle types to the mixed fields around the accelerator and behind shielding were analysed. In an iterative process with the architect the final design of the shielding concept was developed until it was capable of reducing the effect of secondary radiation on humans and the environment below Austrian legal limits

A Shielding Concept for the MedAustron Facility

MedAustron is a synchrotron based accelerator facility for cancer therapy and research in Wiener Neustadt, 50 km south of Vienna. The facility will provide protons up to kinetic energies of 250 MeV and carbon ions up to 400 MeV/n for ion beam therapy. Additionally, protons up to 800 MeV kinetic energy will be used in a dedicated room for non-clinical research. In order to obtain a shielding concept for this facility a detailed geometry of the accelerator facility was implemented into the Monte-Carlo code FLUKA and shielding simulations were performed. In the course of these simulations the contributions of different particle types to the mixed fields around the accelerator and behind shielding were analysed. In an iterative process with the architect the final design of the shielding concept was developed until it was capable of reducing the effect of secondary radiation on humans and the environment below Austrian legal limits

Absolute bunch length measurements by incoherent radiation fluctuation analysis

By analyzing the pulse to pulse intensity fluctuations of the radiation emitted by a charge particle in the incoherent part of the spectrum, it is possible to extract information about the spatial distribution of the beam. At the Advanced Light Source of the Lawrence Berkeley National Laboratory, we have developed and successfully tested a simple scheme based on this principle that allows for the absolute measurement of the rms bunch length. A description of the method and the experimental results are presented

Calibration of a Bonner sphere spectrometer in quasi-monoenergetic neutron fields of 244 and 387 MeV.

This paper describes the results of calibration measurements for a Bonner sphere spectrometer (BSS) with 3He proportional counter performed in quasi-monoenergetic neutron fields at the Research Center for Nuclear Physics (RCNP) at the University of Osaka, Japan. Using 246 MeV and 389 MeV proton beams, neutron fields with nominal peak energies of 244 MeV and 387 MeV were generated via 7Li(p,n)7Be reactions. At high energies, the neutron spectra were measured by means of the time-of-flight (TOF) method. The low-energy part of the neutron spectra were determined by BSS measurements down to thermal energies using the MSANDB unfolding code and three different sets of response functions. These were obtained by means of Monte Carlo (MC) calculations including various codes and intra-nuclear cascade (INC) models. Unfolded BSS fluence rates were additionally confirmed by GEANT4 calculations. For calibration of the BSS, measured count rates were corrected for low-energy contributions and compared with count rates calculated using TOF data and various response functions. In addition, measured response values were compared with mono-energetic response calculations, and best agreement was found with GEANT4 results using the Bertini INC model