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PROTON THERAPY

The Rutherford Cancer Centre Thames Valley 10 Feb 2020
PROTON THERAPY

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Proton therapy is simply another form of radiation therapy, using high energy protons to deliver the dose, instead of X-rays. However, protons have some unique properties that make them useful for treating certain cancers and specific areas of the body.

What is a Proton?

A proton is one of three particles that make up an atom, the others being neutrons and electrons. The proton has a positive charge of +1 and has a relative mass of 1. These properties mean they deliver their energy in a different way compared to X -rays during radiotherapy treatment.

The Bragg Peak?

X-rays (photons) start to deliver radiation dose (absorbed energy) the moment they interact with material (including tissues in our bodies) and continue to deliver dose as they pass through the body and out the other side. The amount of dose decreases steadily as the X-rays pass through more material, but never stops completely.

However, protons deliver a very low dose, until they reach a set depth in tissue (e.g. where the tumour is) and then they deliver all their energy before coming to a complete stop. This behaviour is known as the Bragg Peak effect.

This means the healthy tissues surrounding a tumour do not receive as much radiation as with X-ray treatment. This results in sensitive organs receiving a lower integral dose, which in turn also reduces both short and long-term side effects.

Prostate treatment with proton therapy Brain treatment with proton therapy

               Prostate treatment with protons

 
Brain treatment with protons

Pencil Beam Scanning

Our IBA Proteus One machine has the latest delivery technique called ‘Pencil Beam Scanning’. Here, the target is split into many layers and each layer is ‘dose painted’ with laser-like precision

How is proton therapy delivered?

Like a 3D printer, the target is scanned, layer by layer, so that the treatment conforms exactly to the unique shape of the target. Powerful scanning magnets in the machine head steer the proton beam with sub mm accuracy.

Proton Therapy scan

How do we ensure accurate treatment?

Because protons are highly sensitive to anatomical changes, it is extremely important to ensure the accuracy of treatment by taking X-ray pictures each day.

The Proteus One has cone beam CT which means a 3D ‘CT’ style image can be taken to check that the internal anatomy is exactly aligned, as well as 2D X-ray imaging.

This image is then matched with the CT planning image, and the patient is moved into the final treatment position using a robotic couch to account for any difference in position.

Proton therapy is more effective than X-ray treatment

  • This is not the case as protons work in the same way as X-rays when it comes to killing cancer cells. However they will not cause as much damage to nearby surrounding tissue, meaning in some cases, a higher dose can be given to the target area.

Proton therapy is better for every cancer

  • Proton therapy is most suitable for patients who will experience severe long-term side effects from conventional X-ray treatment, e.g. paediatric patients. However, it is beneficial for some adult cancers.
  • Because proton beam delivery is so precise (due to the Bragg Peak effect) it is not always suitable for areas of the body with a lot of natural movement/motion. Sometimes this motion can be accounted for using specific immobilisation techniques, however, this is not always possible.

Proton myths

Proton therapy is more effective than X-ray treatment
  • This is not the case as protons work in the same way as X-rays when it comes to killing cancer cells. However they will not cause as much damage to nearby surrounding tissue, meaning in some cases, a higher dose can be given to the target area.

Proton therapy is better for every cancer

  • Proton therapy is most suitable for patients who will experience severe long-term side effects from conventional X-ray treatment, e.g. paediatric patients. However, it is beneficial for some adult cancers.
  • Because proton beam delivery is so precise (due to the Bragg Peak effect) it is not always suitable for areas of the body with a lot of natural movement/motion. Sometimes this motion can be accounted for using specific immobilisation techniques, however, this is not always possible.

Find out more on Proton Therapy at Rutherford Cancer Centres

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