What is the synchrotron
The treatment of tumours through hadrontherapy implies the use of a complex particle accelerator, called synchrotron, whose function consists in breaking down the atoms and in creating subatomic particles beams (protons and carbon ions) which are directed to the tumour cells to be destroyed.
The synchrotron technology is similar to that used by CERN in Geneva, but unlike the accelerators used in physics laboratories, the synchrotron was designed and created specifically for the clinical treatment of oncology patients.
The synchrotron supplied to the CNAO of Pavia is the only one in Italy capable of extracting carbon ions from the atom, which are the most powerful particles, for the treatment of tumours resistant to traditional radiotherapy or non-operable. There are only 5 other centres in the world able to do it.
How does the synchrotron work?
The synchrotron, which is located in a 1600-square-metre bunker in the heart of the CNAO headquarters in Pavia, has the shape of a 25-metre diameter and 80-metre circumference ring and is isolated from the rest of the structure with shielding for radiation in reinforced concrete ranging from 2 to 6 metres thick. This shielding is necessary to protect the regular visitor of the centre from radiation hazards.
In two different areas inside the ring there are two devices called "sources", from which the particles beams necessary to carry out the hadrontherapy sessions are generated. Inside the sources is the plasma formed by the gas atoms, which have lost their electrons. These atoms are extracted and protons and carbon ions are selected by means of magnetic fields and radio frequencies. Then the "bundles" of beams are created, each one made up of billions of particles. These bundles are pre-accelerated and sent to the synchrotron where they initially travel at around 30,000 kilometres per second. Subsequently they accelerated to kinetic energies of 250 MeV for protons and 4800 MeV for carbon ions (MeV, equivalent to one million electron volts, is the unit of energy used in atomic and nuclear scale phenomena). To reach this speed, they travel about 30,000 kilometres in half a second, after which they are sent to the three treatment rooms.
How is the patient irradiated?
The beam that hits the tumour cells is a "brush" which acts with an accuracy of 200 micrometres (two tenths of a millimetre). This precision is possible thanks to:
- a continuous surveillance on patient, through infrared cameras that measure three-dimensional displacements
- two scanning magnets which, according to the indications of the beam monitoring system, move the "brush" along the contour of the tumour.
In this way, the tumour is hit section by section: the passage from one section to a deeper one, is obtained by increasing the energy of the beam.
The entire irradiation lasts a few minutes and the number of sessions varies according to the pathology. They are needed for protons on average 35 sessions and for carbon ions on average 16 sessions.