PhD at Creatis and IPNL in Lyon, France
Towards real-time treatment control in protontherapy using prompt-radiation imaging: simulation and system optimization.
Protontherapy is an emerging cancer treatment method that consists in irradiating tumours with proton beams. Although the proton ballistics, thanks to the Bragg peak, allows delivering high dose to the tumours while limiting the energy deposited in the healthy surrounding tissues, uncertainties remain in the proton range and clinicians generally avoid direct exposure of organs at risk behind the Bragg peak. Recently, prompt gamma ray (PG) monitoring is being studied to overcome these limitations. PG are photons created by nuclear fragmentation of the target nuclei. Contrary to the gamma photons used in positron emission tomography (PET), PG are emitted almost instantaneously and cover a broad energy spectrum (up to more than 10 MeV). The works lead by the Lyon Nuclear Physics Institute (IPNL) and the IBA company (with which we collaborate) has shown that the PG depth profile can be measured with dedicated collimated gamma cameras and give information on the position of the dose distal fall off with an accuracy in the millimetre range, on a spot by spot basis. The goal of the thesis is (i) to investigate how to take full advantage of the information given by prompt radiation cameras and (ii) to optimize the camera design and acquisition protocol in clinical conditions. It will allow to provide recommendations for clinical usage of prompt radiation monitoring systems.
MSc at Nikhef in Amsterdam, Netherlands
Proton Imaging with Gridpix Detectors.
Hadron therapy is an upcoming cancer treatment modality with a potentially better spatial accuracy than X-ray irradiation. While an X-ray beam displays a exponential decay in intensity as it traverses matter, a hadron beam has depth profile with a sharp peak, at which point most particles will be stopped. The practical consequence of this behavior is that hadrons allow dose to be deposited more accurately than X-rays. Hadron therapy is therefore well suited to the treatment of tumors located close to sensitive organs. Imaging of the tumor and its surrounding tissue still heavily relies on X-ray CT. To construct a treatment plan for hadron therapy, the X-ray radiodensity map must be converted to a stopping power map for particle beams. This conversion introduces an inherent uncertainty of up to 3%, compromising the improved accuracy that hadron therapy potentially provides. Imaging in the same modality as the treatment would remove this conversion error. This thesis describes the Nikhef/KVI Proton Imager, a device built to measure the hadron radiodensity directly.
BSc at the Van der Waals-Zeeman Institute in Amsterdam, Netherlands
Photoluminescence of Silicon Nanocrystals: The Origin of Different Components.
In this project the photoluminescence (PL) of silicon nanocrystals is studied. It is found that the PL spectrum consists of a band-to-band component and a defect related component. A linear dependence between the excitation energy and the intensity of the defect related component is found. The fraction of excited crystals was kept constant by altering the laser beam intensity. The defect related energy level is probably introduced by oxygen bonds at the edge of the nanocrystal, and possibly lies inside the conduction band. A systematic method of measurement is proposed for future characterization of silicon nanocrystals.