How does proton therapy work?

Proton therapy uses a bundle of proton, positively charged particles, which originate from the core of an atom, and which only emit their maximum dose when reaching a certain depth in the body, after which radiation completely stops (in contrast to photons).


Classic radio therapy uses photons. These are packages of electromagnetic radiation, just like visible light or radiowaves, but with a lot more energy. The emitted radiation dose of a photon bundle decreases gradually as is progresses deeper into the body.

As a result, a limited amount of radiation dose ends up in healthy tissue and also past the tumour in the radiation bundle. Depending on the sensitivity of these tissues and the exposure, side effects might occur.

Thanks to the substantial progress in radiation techniques in recent years, it has been possible to refine the treatment so that it can be administered more accurately. Proton therapy adds another aspect, i.e. the radiation bundle is completely stopped in the tumour, and there is no radiation dose in the healthy tissue 'downstream'.


Proton therapy uses a bundle of protons, positively charged particles that originate from the core of an atom and that delivers its maximum dose when reaching a precise depth in the body after which the radiation stops completely (in contrast to photons).

Bragg piek vs SOBP

This radiation dose peak is called the Bragg peak. The depth of the peak can be determined by modifying the energy level of the proton bundle. The higher the energy of the bundle, the deeper the Bragg people is located in the body. The proton bundle can also be aimed at a specific part of the target volume with the help of dipole magnets in the device. To get an homogenous dose to the target area (the tumour), a rapid succession of a large amount of fine proton bundles with different amounts of energy and position are combined. This technique is called “pencil beam scanning”. In addtion to the position of the Bragg peak, the intensity of each bundle can be modified individually which provides a lot of freedom in terms of adapting the dose distribution to the shape of the tumour.

For administering photon therapy as well as proton therapy several bundles from various angles are used in order to minimise the radiation dose to the surrounding healthy tissue. The big advantage of proton therapy with respect to the current photon therapy is that the healhy tissue located behind the tumour can be spared maximally, making the global radiation load in the case of a treatment with protons lower.

fotontherapie vs protontherapie

This decreases the amount of side effects. The degree in which the chance for side effects decreases, differs from patient to patient. For an individual patient it can therefore be useful to make a comparison between a radiation plan with protons and one with photons to determine the chance for side effects in both types.

How does proton therapy work (in Dutch)


Registration proton therapy

Last edit: 16 April 2021