SCK•CEN, the Belgian Foundation against Cancer as well as various Belgian Universities involved in applied clinical research have recently created a Belgian HadronTherapy Consortium (BHTC). The creation of a hadrontherapy treatment unit in Belgium meets a real need. However, the cost of building and running a combined proton/ion therapy centre makes it necessary to opt for a single structure for the entire country. SCK•CEN is actively participating in the discussions around the feasibility of a Belgian hadrontherapy project.
'Hadrontherapy' is a collective word that describes the many different techniques of oncological radiotherapy which make use of fast non-elementary particles made of quarks: protons, neutrons and light nuclei are the hadrons used to locally control many types of tumours. The BHTC is currently involved in the preparation of a 2 year feasibility study in which SCK•CEN is actively participating by bringing its welknown expertise in nuclear engineering, radiobiology and dosimety.
In the history of radiation therapy there are many examples of how cure rates have been increased through improvements in physical dose distribution and the resulting increase in feasible tumor dose. In many cases, however, an exact fit of the irradiated volume to the target volume is impossible due to the physical characteristics of the gamma rays or electron-bremsstrahlung used in therapy. After a short buildup, the dose progressively decreases at greater depth.
Beams of charged particles (protons or ions) produce a much more favorable dose distribution. For protons and ions, the delivered dose increases at greater depth, and then declines abruptly beyond a sharply defined maximum known as the Bragg peak. The location of this maximum in the patient’s body can be precisely determined by the energy of the particles. In addition, protons and ions exhibit a small lateral and range scattering, which is another prerequisite for achieving a tumor conform treatment. These physical properties of charged-particle beams make it possible to substantially increase the tumor dose while at the same time reducing the integral dose in healthy tissues.
In addition to the favorable physical dose distribution, a specific high-LET effect becomes effective in the case of ions as distinct from protons. This manifests itself by an increase of the relative biological effectiveness (RBE) that in turn allows higher curative success rates for well defined indications. Amongst these indications are hypoxic tumors, slowly growing tumors, and tumors being less or almost non-responsive to conventional photon therapy.
As a result of its high precision and the specific high-LET effect, radiation therapy with ions is recognized as the treatment of choice for slowgrowing, inoperable, radiation resistant tumors (e.g., chordomas and chondrosarcomas), especially in the vicinity of high-risk organs like the brain stem, optic nerve or spinal chord.
Minimizing uncertainty on healthy tissue response to protons and carbon ions is necessary to expand the applications of hadrontherapy in curing cancer. It is planned to compare the biological effects of protons and carbon ions with X-rays in different normal versus cancer tissue cells (central nervous system, lung, gastrointestinal, haemotopoietic) using in vitro models and to transfer the experimental results in mathematical models used in the treatment planning for protons and carbon ions. In vitro experiments are necessary to understand the biological mechanisms involved in the effects of protons and carbon ions.