The performance of hydrostatic bearings is in part decided by their lubrication-film height shape. Imaging the shape can be done by dissolving fluorescent dyes in the layer. However, current imaging techniques are rooted in heuristics, and as such, their physics, design parameters, and error sources are not quantitively understood. To fully grasp and consequently design the ultimate measurement system, the governing equation—the fluorescent radiative transfer equation—is solved analytically for a plane-parallel system. The new solution method assumes that fluorescent radiative transfer is well-described by the first two photon generations. Verification is done experimentally and by a concurrent Monte Carlo method. The model also successfully predicted the response of a real measurement setup. Further model analysis led to the understanding of factors such as: camera positioning; light source design; and the effect of the reflective background on which the lubrication layer lays. The insights suggest a practical implementation for a dynamic imaging setup.

The main challenge of radiotherapy, used for treating cancer, is to deposit the prescribed dose in the tumor volume while sparing the surrounding tissue.The depth-dose distribution of protons makes proton therapy an alternative to conventional radiotherapy for some tumor sites. A better knowledge of the proton radiobiological mechanisms can improve the effectiveness of radiotherapy treatments.

Holland Proton Therapy Center (HPTC) is one of the Dutch proton therapy centers. One of the purposes of its experimental beamline is to perform radiobiological experiments. To conduct different types of pre-clinical experiments, the beamline must be equipped to provide large field irradiation with precise dose characterization. Moreover, having a reliable Monte Carlo(MC) model of the system allows to perform in silico verification of the beamline design and contribute to its optimization. In this context, the goals of this project were: implementing a dual-ring scattering system in the experimental room of HPTC to produce homogeneous fields of different sizes; creating a MC model of the HPTC passive beamline able to reproduce the experimental setup.

A dual-ring double scattering system was implemented in the HPTC horizontal beamline, starting from a single 150MeV pencil beam. The resulting passive irradiation fields were characterized by measuring and analyzing the lateral beam profiles, the depth-dose distributions and the relative dose at target position. Moreover, the beam characteristics and setup were implemented in theTOPAS MC code. The beam source parameters, input of the MC model, were found by comparing the experimental and simulated beam envelope and depth-dose distributions of the pencil beam. Then, the passive system model was benchmarked with experimental data by evaluating the lateral profiles, Braggcurves and dose distributions.

The results show that the implemented passive system can achieve dose uniformity between 96% and 99% for field sizes between 4x4cm² and 20x20cm²for a 150 MeV proton beam. Moreover, using a collimator with a 5x5cm²aperture, uniformity of at least 97% in the different Bragg peak regions is achieved. Good uniformity is also obtained for beam energies in the range 115MeV-150 MeV, showing robustness of the setup. Furthermore, the range of the proton beams traversing the beam-shaping elements, as well as the energy arriving to target, were studied. Moreover, with a ridge modulator, Spread-OutBragg peaks were obtained with a width up to 3,4cm and of uniformity 98,5%.

The MC model produced in TOPAS was first benchmarked against a 150MeVproton beam in air. Secondly, the experimental data of the large fields were compared with the simulated ones. The simulation of depth-dose distributions and lateral beam profiles agreed with the experimental data. Furthermore, the model was used to estimate the number of initial protons required to achieve an experimental dose and to estimate the location of the Bragg peaks.

All in all, the dual-ring passive scattering setup has been successfully implemented and is ready to be used to perform radiobiological experiments. Also, the TOPAS MC model can be used to assist in the preparation of these experiments and to further optimize the beamline design.