Proton Therapy

The aim of radiotherapy is always to destroy the DNA in the tumour cells in order to stop their ability to divide and thus grow. To do this, energy packets or particles are brought to a very high energy level in so-called accelerators so that they can penetrate the diseased tissue and do their work there. The advantage of radiotherapy is that it is localised and thus only affects a specific, defined area of the body: in the tumour itself. This reduces side effects and distinguishes radiotherapy from chemotherapy, which has a different (‘systemic’) mode of action, acting throughout the human body. Spreading the radiotherapy dose over several radiotherapy sessions reduces the side effects even further, making radiotherapy more tolerable for the patient.

Different tumours require different dosages

During radiotherapy, energy packets or particles are brought to a very high energy level in so-called accelerators so that they can penetrate the tissue and do their work there. The absorbed dose is measured in ‘Grays’ (abbrev.: Gy), which is the unit of measure indicating the dosage of radiation treatment. In radiotherapy, some tumours can be impaired by a low dose of radiation, whereas other tumours require a very high dose. This means that different tumours have different levels of sensitivity to radiation, therefore requiring different radiation dosages depending on the type of tumour involved.

What is proton therapy?

Proton therapy, also referred to as proton treatment, is a modern form of radiotherapy for treating tumours in cancer patients. Its physical properties mean it can offer various benefits compared to photon-based radiotherapy:

• It is extremely precise as the protons can be aimed at the diseased tissue with millimetre precision.
• It can therefore mean fewer side effects.
• It ensures efficient tumour treatment as the surrounding healthy tissue is spared as much as possible.

Photon-based radiotherapy has been used for decades in treating tumours across the world. There are currently five facilities in Germany, of which WPE at the University Medical Centre of Essen is the largest. Its expertise in the field of research and its wide range of proton therapy applications – such as pencil beam scanning – have helped make WPE a highly respected treatment centre and a leader in proton irradiation.

Mode of action and the benefits of proton therapy

Proton therapy differs from conventional photon-based radiotherapy in many respects:

1. Less energy absorbed by healthy tissue

Proton-based treatment offers the key benefit of having only minor effect on healthy tissue. The reason for this lies in the focused proton beam which emits very little energy on its way to the diseased tumour cells. Most of the energy is discharged directly at the intended location – within the tumour itself.

As soon as the beam reaches the tumour, it stops abruptly (Bragg peak), meaning that the healthy tissue surrounding the tumour is exposed to significantly less radiation – both before and behind the tumour.

In radiotherapy using photons, the energy is emitted immediately it enters the body, meaning that healthy tissue receives comparatively more radiation. Neither can photons be stopped immediately after passing through the tumour.

2. Precise speed control

Since tumours can be located at different depths in the body, the proton beam must be adjusted precisely to this depth. This is done via the speed. The deeper a tumour is located, the higher the speed of the proton beam must be.

This means the penetration depth of the protons can be adjusted precisely and the proton beam can be adapted precisely and individually to suit the shape and position of the tumour. For maximum efficiency in cancer treatment.

To enable this to be calculated, a team of case doctors and physicists always localises the exact position of your tumour before the actual proton therapy commences. This is done using CT and MRI images created specially for each patient.

With the help of these images, it is possible to determine the exact proton speed required for successful irradiation. This means the penetration depth of the protons can be adjusted precisely and the proton beam can be adapted precisely and individually to suit the shape and position of the tumour. For maximum efficiency in cancer treatment.

In clinical operation, protons can also be superimposed with different energies (stopping at different Bragg peaks). This means that even an extensive tumour can be irradiated evenly and with millimetre precision – for maximum protection of surrounding tissue and the best possible therapeutic outcome.

3. Greater penetration depth

In contrast to conventional radiotherapy using photons, protons can penetrate much deeper into human tissue. Up to 30 cm deep. This means that proton therapy can also be used to irradiate deep-seated tumours effectively and with few side effects.

4. Gentler treatment for children

Especially for children with cancer, it is important to protect healthy tissue as much as possible during radiotherapy. Because children are still growing, irradiating healthy organs can have far-reaching consequences:

• Circulatory disorders
• Mutations in the central nervous system
• Growth and metabolic disorders
• Deterioration of hearing and vision
• Dental, orthodontic and mouth disorders
• Secondary tumours
• etc.

With proton therapy, disadvantages in the form of such late complications and long-term consequences are reduced to a minimum. This is because the lower energy output in front of the tumour and precise control of the proton speed make it possible to irradiate the child’s tumour as precisely as possible – for efficient, gentle treatment offering the best possible chances of recovery. This gentle treatment also makes the child’s time during radiotherapy easier, as acute side effects are also minimised. However, even with proton therapy not all side effects can always be avoided. In certain constellations, a balance may have to be struck.

Which diseases can be treated using proton therapy?

To date, almost 300,000 patients across the world have been treated successfully using protons. With technical progress and increasing investment, proton therapy is becoming more and more widely available, and the number of indications – i.e. the medical conditions for which it represents a viable alternative therapy – are also increasing steadily.

Very good results have been achieved with proton therapy, particularly on deep-seated tumours and on tumours surrounded by important or sensitive parts of the body. These include primarily tumours in the head, spinal column and pelvic area (i.e. mainly primary brain tumours) as well as sarcomas of the base of the skull, facial bones, spinal column and pelvis.

A standard indication for proton therapy is the treatment of uveal melanomas. Prostate and nasopharyngeal carcinomas are also suitable for treatment with proton therapy. In both cases, patients benefit from the precision of proton radiotherapy, as the bladder and bowel as well as the optic and auditory nerves can be spared as far as possible.

The same goes for the pituitary gland which is important for the production of hormones throughout life. It can be spared to best effect when proton therapy is applied to the head. As young tissue in children is particularly sensitive during the physical development stage, young patients – and in some cases very young patients – are an extremely important demographic when it comes to proton therapy. Here, proton therapy can be used to achieve the best possible avoidance of late complications and side effects.

Proton therapy and side effects

Radiotherapy is always accompanied by certain side effects. Depending on the area being treated, this can include nausea and vomiting, and also tiredness, fever and hair loss. Late complications such as secondary tumours can also occur. It is therefore all the more important to reduce these side effects to an absolute minimum, and to this end – depending on the indication – proton therapy is usually the treatment of choice. Patients generally tolerate proton treatment well. As far as the tumour itself permits, as a patient you can usually go about your everyday life without too many side effects. That said, acute side effects can occur, for example if you are taking additional medication or receiving chemotherapy. In any case, always talk to your case doctor if you experience any side effects during treatment.