Tuesday 28th April 2015
Mac Voice, the magazine for Macmillan professionals: Spring 2015
Yen-Ching Chang on the benefits of proton therapy and its current provision in the UK
What is proton beam therapy?
Proton beam therapy is a form of radiotherapy. The main principle of radiotherapy is careful targeting so that, while the cancer receives a sufficiently high dose of radiation, the dose received by adjacent normal tissues and organs is kept as low as possible, reducing damage.
Radiotherapy is normally given using high-energy x-rays. Instead, proton beam therapy uses high energy particles to irradiate tumours (expose them to radiation).
How is it different to x-ray radiotherapy?
Proton beam therapy is able to target cancer far more precisely than conventional radiotherapy. X-rays behave like light, travelling in straight lines.
So to treat a tumour, the normal tissue both in front of and behind the cancer will receive a dose of radiation too. Protons behave very differently, depositing virtually all their energy at a certain depth within tissue.
This depth can be changed so it coincides with the depth of the cancer within the body. This means that normal tissues lying beyond that depth receive virtually no radiation.
In this way, proton beam therapy can effectively target cancer while sparing normal tissues from being irradiated.
Who would benefit from proton therapy?
People who have tumours which lie next to critical structures would now be able to receive an adequate dose of radiation. A critical structure being an organ (or part of an organ) which, if damaged, may lead to life-threatening complications.
The dose of x-ray radiation used is limited by the dose that the surrounding normal tissue can tolerate. Proton therapy can deliver a higher dose of radiation, while still keeping the dose to the normal tissues within tolerance.
This would lead to an increase in cure rates. Chondrosarcomas and chordomas that are located in the base of the skull fall into this category, as they need high doses of radiation but the brain stem, optic chiasm and optic nerves are often in close proximity to these tumours, and have a lower tolerance to radiation than the doses needed to control the primary tumour.
Proton therapy in this instance is able to deliver high doses of radiation to the tumour while not exceeding the tolerance of the nearby critical structures, leading to better cure rates for these tumours.
The other group of people who would benefit are those in whom radiotherapy has led to a cure, but with significant long-term side effects following treatment.
Some of these side effects may develop months or years following treatment. These can be permanent and very debilitating. In particular, children, teenagers and young adults would stand to gain significantly from the use of proton beam therapy.
This is because irradiating developing tissues may result in significant long-term effects such as problems with growth, IQ, development through puberty, heart and lung damage as well as an increased risk in the development of a second tumour or cancer.
Worldwide there are more than 20 high-energy proton therapy centres in operation, with centres in the US, Switzerland, France, Germany, Japan, China, Italy, South Korea, Sweden and the Czech Republic and many more in the construction and planning stages.
In the UK there is a low-energy proton facility at The Clatterbridge Cancer Centre, which has a highly successful programme in treating superficial eye tumours, but there are currently no high-energy proton facilities. However, since 2008 the NHS has funded travel abroad for treatment of particular tumours with proton beam therapy.
These tumours include:
- chordomas and chondrosarcomas in the base of the skull, and bone and soft tissue sarcomas around the spine in children and adults
- brain tumours in children, such as ependymoma, low grade glioma and craniopharyngiomas
- other tumours affecting children, such as rhabdomyosarcomas and Ewing’s sarcoma.
Full details of the current NHS guidance can be found at on the NHS website.
So far more than 400 patients have benefited from this programme allowing them to receive treatment overseas.
Future plans for UK services
It is recognised that there are more people who would benefit from proton beam therapy than can be sent abroad. In 2012, the government announced that University College London Hospitals NHS Foundation Trust and The Christie NHS Foundation Trust in Manchester will provide a national service for proton beam therapy opening from 2018.
The cancer types that will be treated are those in which it is felt that there is clinical benefit in terms of cure rates and/or a reduction in long term permanent side effects.
These include those cancer types already being sent for proton beam therapy abroad with some additional brain tumours, sarcomas, head and neck cancers as well as particular consideration of children, teenagers and young adults requiring radiotherapy.
As with other forms of radiotherapy, a radiation mask can be used when proton beam therapy is given to the head and neck area
It is important to bear in mind that proton beam therapy (like any form of radiotherapy) often needs to be given as part of a bigger package of treatment alongside chemotherapy and surgery. The timing of each part of the treatment package can be critical.
Therefore pathways related to the delivery of proton beam therapy are complex, requiring input from different clinical and supporting specialities to ensure the best outcomes for people with cancer.
Email Dr Yen-Ching Chang, Consultant Clinical Oncologist and Clinical Lead on Proton Beam Therapy, University College London Hospitals (UCLH).