The High Flux Reactor (HFR) in the sand dunes near Petten. This nuclear reactor is owned by the Europeaan Commission and is used mainly for the production of radioactive isotopes, to be delivered to hospitals for diagnostics and the treatment of cancer. The reactor in Petten provides a third of the world production of radioactive isotopes for medical use.
The nuclear reactor produces intense neutron radiation which, after processing with an energy filter, can be used for radiotherapy treatment. From 1992 to 1995, the Netherlands Cancer Institute (NKI) is involved in the preparations of a clinical trial with Boron Neutron Capture Therapy (BNCT) in Petten. The Radiotherapy Department of the NKI has the expertise in dose measurement of neutron beams, obtained from the use of the experimental neutron generator between 1976 and 1981. Also, there is considerable experience with the physics-technical and organisational aspects of radiotherapy.
The NKI physicists Ben Mijnheer and doctoral student Niels Raaijmakers develop the dosimetry in the neutron beam and a method of dose computations with the treatment planning system. A taskgroup is formed to advise on the realisation of the treatment room, the irradiation accessories and the small out-patient clinic which is built next to the dome of the reactor. Members of the taskgroup are: Luc Dewit (radiation oncologist), Riet van der Heide (head radiation therapist) and Henk van der Gugten (technical specialist).
The High Flux Reactor (HFR) with irradiation facility in Petten.
The building and technical facilities for BNCT treatment in Petten are in particular an energy moderator in the neutron beam based on fluid Argon, a beam shutter, the treatment room, a special treatment table, a control room for the medical staff and an external building with out-patient facility. The passage between the external building and the reactor building is provided with an air lock with hermetically closing doors. For this the existing emergency exit of the reactor dome is used. In the reactor building there exists a low pressure to prevent, in the case of an accident, radioactive gases escaping into the outside air. The design and realisation is in the hands of the reactor group of NRG in Petten.The NKI advises in clinical and practical aspects.
The treatment room for BNCT treatment.
The irradiation room is clad with (white) polythene plates which absorb neutrons. The neutron beam arrives from the reactor nucleus through the round opening in the wall on the right. The isocentrically turning table is contsructed from materials which, when irradiated by the neutron beam, will become minimally radioactive. The NKI provides the head and neck fixation with individually made-to-measure masks and lasers with which the patient can be positioned.
The principle of BNCT treatment: In an ideal cancer treatment, all tumour cells will be selectively removed or destroyed, without damage to healthy tissue. The existing treatments with surgery, radiotherapy and chemotherapy have side effects which often make a radical cure impossible. In the search for the ideal treatment during the 1990's, there is renewed interest in the possibilities of Boron Neutron Capture Therapy (BNCT). Already in 1936 the principle of this, in theory, elegant method had been formulated by G.L. Locher of the Franklin Institute in Pennsylvania . With a selectively acting drug, the stable isotope boron-10 is injected into the tumour tissue. On irradiation of a boron-treated cell by so-called epithermic neutrons with an energy of 0.5 to 10 keV, the B-10 absorbs the neutrons and energetic alpha particles and lithium ions are released. This secondary radiation does not reach much further than the dimensions of the boron-treated cell which is thereby destroyed. Non boron-treated healthy cells survive this treatment. The BNCT treatment is mainly studied for application in brain tumours ( glioblastoma multiforme) which have a low sensitivity to conventional photon radiation. In practice, it appears that the boron injection is not without side effects and that the damage to healthy tissue is not negligible. Worldwide clinical and experimental research into possible forms of BNCT is still on-going, but the NKI is no longer involved in this.
Treatment planning for neutron beams.
With adaptations to the Plato treatment planning system (Nucletron) it becomes possible, with the programs for external photon and electron beams, to make computer calculations of the dose distribution for the neutron beam. The calculation programs are based on the work of Rob van der Laarse and Iain Bruinvis, in which the parameters of the calculation model are adapted to the dose measurements in the clinical neutron beam. The result of the dose calculations is an acceptable approximation of the actual dose measurements.
Physicist Niels Raaijmakers at work, measuring the neutron dose in an artificial head.
The artificial head has been designed by the physicists in the NKI. The production is a work of art by the instrument makers of the Department of Radiotherapy. Instrument makers Leo de Mooij, Erik Kos and Peter Groote made this artificial head using a computer-controlled milling machine. The design is based on a digitally derived contour from the CT scan of a standard phantom of a human head (the so-called Alderson phantom). The supporting cushion is also made according to shapes which have been determined on the CT scanner. The introduction of this production technique in the NKI made it possible also in conventional radiotherapy to use anatomically formed and accurately fitting cushions and accessories.
More information about BNCT treatment can be found on the following websites: