Irradiation of a malignant tumour with ionising radiation is standard in cancer therapy. Usually, one uses photon or x-rays to cause damage to cells and the genetic material of the tumour. In the future, however, proton beams are able to cover a wide range of indications, because they are particularly suitable due to their unique physical properties.

X-ray and proton beams have something in common. They can be targeted very precisely in a particular direction. The essential difference is, however, that with protons – unlike X-rays – the range is precisely controlled. This is due to the fundamentally different physical properties of electromagnetic waves (X-rays) and accelerated nuclear particles (protons).

The History of Proton Therapy

Proton therapy is not an entirely new method: In 1946, Robert Wilson, a physicist, already reported on the beneficial properties of proton radiation. Since 1954, protons have been clinically applied in the United States. So far, more than 106,000 patients have been treated with protons. There are now about 30 plants worldwide that treat cancer patients with protons or other particles. In Germany, there are currently five new plants under construction or in development. Due to a combination of research and application of proton therapy, the WPE is a unique center and is a nationwide leader in the field.

Treatment with Protons

The elemental accelerator, the cyclotron located in the basement of the WPE, accelerates from the atoms of protons obtained from hydrogen gas in approximately 60% the speed of light. Please note: a human would be able to travel the world 4 times in one second at this speed. In the treatment rooms (gantries), the jet head can be precisely adjusted and rotated 360 degrees. Thus, the proton beam can penetrate into areas of the body that would otherwise be difficult or impossible to operate on.

The proton beam penetrates the healthy tissue and discharges its largest energy directly in the tumour and then abruptly stops (Bragg peak). The penetrated tissue and the tissue behind the tumour only experience a low radiation exposure.

Technology: „Behind the Scenes“

The proton source of the WPE is a cyclotron from the IBA with a constant energy level of 230 MeV. An energy selection system is turned on to adjust the range of tissue. The beam is guided via a transport system with focusing and deflecting magnets and the associated monitoring system leads to the respective irradiating head. Here, the proton beam is adjusted to the target volume via active or passive beam scattering. Hereby, the beam quality and position are monitored within narrow boundaries.

Techniques of Proton Therapy

A total of four treatment rooms (gantries) with various proton modalities, 3 of which can be rotated by 360 degrees, will be put into operation at the WPE by the end of 2015. In addition, the WPE has the possibility of image guidance using X-ray, CT and MRI. The WPE not only has 2 CT’s, 2 MRI’s, a digital X-ray and a fluoroscopy, but also laser systems, surface recognition systems and respiratory triggering of the treatment beam in all rooms. In the future, the WPE will then be able to treat tumours of moving tissue, for example in breathing lungs. This will be made possible by the active scanning method, comparable to the delicate brushwork of a painter. This ensures the highest accuracy, but also takes a long time to process.

The other method, the more widespread diffusion sheet method, on the other hand, is great for eye tumours. Between two eyelashes, the proton beams are shot directly at the tumour.

The WPE is the only centre in Germany that utilises different proton processes for application, depending on what method is optimal for the respective patient.

Radiation Protection

With regard to the sensitive environment of the WPE – University Hospital Essen – detailed computer simulations of radiation protection have been performed before commissioning.

The calculated radiation dosage coming from the WPE in one year is 0.1 mSv at the plot’s boundary line. For comparison, this dosage is even achieved during a single long-haul flight. Although a computer can simulate low dose contributions, it is not likely that they are measured. However, the dose is regularly monitored by us.