Characterization of the proton beam line in the experimental room of HollandPTC

Characterization of the proton beam line in the experimental room of HollandPTC

Ibrahimi, Atia (TU Delft Mechanical, Maritime and Materials Engineering)

Lathouwers, D. (mentor)
Rovituso, M. (mentor)
Smith, A.L. (graduation committee)
Parnell, S.R. (graduation committee)
Groenendijk, C.F. (graduation committee)

Delft University of Technology

Biomedical Engineering

2020-12-01

As protons have a localized depth-dose distribution, proton therapy nowadays is a form of radiotherapy that is being implemented for part of the cancer patients. Compared to photon therapy it allows more precise targeting of tumours and sparing of surrounding healthy tissue. Besides patient treatment, research on proton therapy topics is being done to gain more knowledge on and keep improving the technique. Since the 1950s almost 100 proton therapy facilities are operating clinically worldwide. One of those facilities is HollandPTC, a proton therapy center located in Delft, The Netherlands. The ProBeam Varian cyclotron serves two treatment gantries, an eye treatment room, and a research experimental room. The experimental room is dedicated to research topics in the proton therapy field and is equipped with a fixed horizontal beam line that can be used for physics experiments and also for radiobiological experiments. In order to perform those types of research the beam needs to be fully characterized in terms of dose, shape, size and energy, this is the purpose of this work. The second goal was to commence with a setup for creating homogeneous fields by means of passive scattering and determine the optimal distances required between the elements of the setup. The single pencil beam characterization has been done by performing a large variety of experiments, making use of setups with different types of detectors. The experiments include beam spot, beam envelope, beam current, and depth-dose distribution measurements, and have been performed for nominal beam energies between 70 and 240MeV. For the passively scattered field a dual ring setup has been implemented. Spread-out Bragg peaks have been created with a ridge filter. An energy of 150 MeV was used, as the scattering elements have been designed for this energy specifically. The single pencil beam characterization resulted in beam spot sizes at the isocenter varying from 3.54 mm for 240 MeV, up to 5.47 mm for 70 MeV, with an asymmetry of 1.7% at most. The beam envelope measurements showed that the beam spot size just after the exit window is 2-3 mm and diverges up to 12 mm at 2 m from the exit window. The beam current measurements gave the transmission efficiency of the system, ranging from 0.04% for a 70 MeV beam up to 5.6% for 240 MeV, increasing exponentially. The depth-dose measurements provided the difference between the nominal beam energy and the beam energy at the isocenter. The difference becomes smaller as the nominal beam energy increases and is 2.4% for a 70 MeV nominal beam and 0.3% for a 230 MeV nominal beam. With the dual ring setup fields of up to 25 cm in diameter have been formed with a uniformity of at least 97%. The ridge filter created a spread-out Bragg peak of 2.8 cm with a uniformity of 98% and also gave good results for other beam energies (100-200MeV). It can be concluded that the goals of the project have been reached as the beam has been characterized in terms of shape, current, and energy. Also some preliminary work for the passive field has been accomplished. The work on the dual ring setup can be further expanded by placing the ridge filter and a collimator in the setup, after which the field can be characterized in terms of dose. The results obtained from the single pencil beam characterization allowed for the first physics experiments to start at the experimental room of HollandPTC during the last year.

Proton Therapy
Radiotherapy
Proton beam
Passive field
Pencil beam
Particle Therapy
Cancer
Radiobiology

http://resolver.tudelft.nl/uuid:34e200d1-f744-4685-b4d0-2cfa2efce158

51.99069400054972,4.383651842489914

Student theses

master thesis

© 2020 Atia Ibrahimi