Treating Brain Tumours With Proton Beam Therapy

What has been highlighting the news recently is the Ashya King case and the implications of certain therapies to treat brain tumours. Ashya King is the five year old son of parents Brett and Naghemeh King. Whilst Ashya was being treated in a UK hospital, his parents, without consent from doctors, took him from hospital and journeyed overseas to seek the treatment they wanted for their son. Mr and Mrs King were in preference for proton beam therapy for their son - this directly targets cancer cells and is considered to have less side effects than the conventional radiation/X-ray therapy. However currently in the UK, proton beam therapy isn't available for the treatment of tumours like Ashya has -  instead it has only been used to treat certain eye conditions. Government legislation says that proton beam therapy will be introduced in combating cancers like Ashya has by 2018. Understandably, Ashya's parents simply cannot wait that long for the treatment; it is important to intervene as early as possible when tackling a tumour as severe's as Ashya's.

What is proton beam therapy?

X-rays have long been used to treat cancerous tumours. Given in sufficiently high doses, X-rays will be able to kill tumour cells, however what many people view as a fundamental flaw is that healthy tissues can be exposed to similar intensity radiation. This leaves risk of healthily tissue being destroyed which can in turn be potentially detrimental to health. Therefore many people believe proton beam therapy to be the best option, as even in high concentrations there is greatly reduced damage to healthy tissues (and more importantly, the vital organs). The problem that arises is that those receiving X-ray therapy will receive a lesser dose than desired by doctors as the risk to healthy tissue comprises the treatment. Many patients desire proton beam therapy partly because of this.

Recalling fundamental chemistry, protons are subatomic particles of the atom which are positively charged. They have a relative charge of +1. Opposing this, 'orbiting' electrons have a relative charge of -1, and thus the two subatomic particles have an attraction for each other. Having this rather basic intuition allows us to make sense of how proton beam therapy works. As charged particles, such as protons are fired near other molecules or atoms, they become attracted to the elections with orbit the atoms. This causes the atoms to ultimately lose electrons and as a result become positively charged. These are now ions. Obviously, this process is therefore called ionisation which causes the chemical properties of that atom to change. This is vitally important when targeting cancer cells. As the proton beam targets the cells, the molecules within those cells become damaged, or ionised. However it matters what molecules become affected, for example to damage the DNA of a cancer cell means destroying it's functionality. As a result, key processes such as mitosis (cellular division) and DNA replication become disrupted. With a high enough dosage, no matter how hard enzymes work to repair the damage, their efforts become futile. Cancer cells have less capability of repairing damage to organelles and molecules than healthy cells, which means minimal concern for the normal cells that are bombarded with the proton beam. Fundamentally, the proton beam creates a selection pressure on cancer cells, they are more likely to be destroyed and subsequently their numbers decline. 

Although both X-rays and proton beams aim to target cancer cells, it is considered that the precision and accuracy of the proton beam is greater. The 'distribution of protons can be directed and deposited in tissue volumes'. Another downfall with X-rays is that as they 'lack charge and mass', their use results in radiation being deposited 'in normal tissues near the body's surface'. This ultimately poses a risk of genetic mutation to healthy cells.

Interestingly, protons can be accelerated or decelerated as and when required - X-rays cannot be 'energised to specific velocities' unlike protons. This property of protons allows physicians to have some element of control as to how penetrative the proton beam is. As a very physical entity, protons slow down as they penetrate further into tissue, coming into contact with more electrons as a result. It follows that as the protons decelerate, they eventually stop at their designated site - the cancer cells. This is not the case with X-rays as some radiation is left to pass through the tumour tissue and through to other healthy tissue via an "exit dose" before exiting the patient completely.

I have empathy as to why the parents of Ashya want to pursue this proton beam therapy. With fewer side effects and less damage to normal tissue, it is highly likely that Ashya would enjoy 'a better quality of life during and after proton treatment'.


Credit to the BBC on their updates on the Ashya King case and to The National Association for Proton Therapy for their article 'How Proton Treatment Works'. Read more on the subject here.

Image: Patient receiving radiation therapy - BBC