Proton therapy in Wallonia

Eliott Ramoisiaux

Proton therapy is, according to experts, the best therapeutic intervention in the case of various cancers, particularly paediatric cancers, because it minimises the risk of secondary cancers. More generally, it offers the high precision required when radiotherapy treatment must target a cancerous lesion within sensitive organs (cranial and cervical lesions, eyes, brain). In many other cases, it should ensure the best therapeutic cost-effectiveness ratio.

In this context, it was decided to create a technological innovation partnership that would be structured around a proton therapy facility that would constitute a research and development platform in the clinical, industrial and radiobiological fields, and could constitute a training centre available to both clinicians and technicians. This linkage could make it a reference facility at European level.

PROTHER-WAL will develop research along three lines, technological, biological and medical, in order to gain a better understanding of the physical and biological phenomena induced by proton therapy, to improve existing technologies and to promote synergies with other therapeutic methods or diagnostic tools, in particular functional imaging.

These different aspects will be studied in particular in the context of individualised medicine. Individualised medicine is characterised by the use of treatments adapted to the specific characteristics of each patient, in order to minimise failure rates. Thus, more specific treatments, adapted to each individual, can be developed, similar to what is already being done in the context of surgery. Proton therapy lends itself particularly well to this type of approach because it allows precise focusing and adjustment of the dose, and thus, used in synergy with precise imaging methods, can allow the protocol to be adapted to the patient, and thus optimise the treatment while limiting the effects on the surrounding healthy tissue

From a technological point of view, the research will aim, among other things, to adapt the equipment to other targets, small animals and materials. This adaptation, which is unique at present, will provide the necessary tools for a better understanding of the technology, both at the physical, biological and medical levels.

A large part of the research will also be dedicated to clinical studies, at the "proof of concept" stage, which will make it possible to broaden the range of cancers that can be beneficially treated by proton therapy.

Ion beams of 1 to 200 MeV can be used to modify the properties of materials or to carry out tests on their performance under ionising radiation, for example for the space industry. The studies for space applications will mainly involve irradiation testing of electronic components and coatings for the space industry. These measurements will be carried out at different energies between 30 and 200 MeV. These energies are required to model SEE (Single Event Effects), which is one of the main degradation phenomena for space systems subjected to solar wind.

The consortium will also study the activation of the elements of the proton therapy centre structures in order to be able to optimise the choice of materials used for the layout of the proton therapy centres. The characteristics in terms of beam size and, above all, energy modulation will make it possible to combine ion beam analysis techniques such as PIXE (Particle Induced X-ray Emission) and PIGE (Particle Induced Gamma Ray Emission) in the high-energy mode in order to monitor the changes in irradiated materials in real time. The use of high-energy beams (> 5MeV) will make it possible to analyse the effects at greater depths than via conventional techniques. These studies can therefore also be extended to other fields of research, particularly for the analysis of cultural heritage objects. As with the study of space components, the PBS (Pencil Beam Scanning) mode will make it possible to measure and modulate precisely the dose received by each element of the irradiated systems.

Within the framework of these studies, a positioning system will be developed and installed initially on the ULg cyclotron before being set up at the proton therapy centre. In parallel, numerical modelling of the interaction of protons with the materials envisaged will be carried out.

In addition to the direct effects of the protons, the interaction of the proton beam with various elements of the accelerator line (beam losses inside the accelerator itself or in the deflection and focusing lenses, interaction with the degrader, etc.) produces radioactive isotopes, some of which have a long life span, but also a significant flow of secondary neutrons. These neutrons interact with the shielding and with all the equipment present in the treatment room (and possibly in neighbouring rooms), which leads to activation of these different materials and equipment. It also has a significant impact on the decommissioning of the installation, as the eventual need to treat tonnes of concrete as radioactive waste can be extremely costly.

To reduce the activation of the concrete shielding, a particular design will be tested in this project. The inner concrete layer of the shielding (most exposed to neutron fluxes, typically 50 cm thick) will be made of concrete with low levels of impurities at the origin of the concrete activation (e.g. europium). In addition, gypsum panels (typically 20 cm thick) will be placed on the inner surface of these walls (to moderate and attenuate the incident neutrons).

The activation of the shielding and the accelerator line elements will be studied in detail (experimentally and by numerical simulation) within the framework of this project. In order to be able to precisely quantify the fluences (of neutrons in particular) received by these different materials, precise monitoring of the proton currents but also of the neutron fluxes must be put in place. Numerical simulations will be carried out using the Monte Carlo codes most commonly used in the field (MCNP-X, GEANT4, FLUKA, PHITS), with each partner focusing on the codes for which they have expertise. As these simulation codes differ in the numerical implementation of the physical interaction processes, the simulation results will be subject to detailed critical comparative analyses. From an experimental point of view, neutron flux (and dose rate) measurements will be carried out (pellet activation, dose rate measurements using WENDI-II detectors adapted to the measurement of high energy neutrons). Low-activity gamma spectrometry measurements will also be carried out (e.g. cores taken from the shielding) using HPGe detectors in particular. These various simulations and measurements will allow a better quantification of the activation of the shielding materials and the accelerator line, and will make it possible to test the devices put in place to reduce the activation of these shieldings.