Photon vs proton

The couple were detained in Spain after an international manhunt that drew condemnation in British media, separated from their sick son and then released days later by a Spanish judge.

They arrived with Ashya in Prague last Monday and visited the clinic to begin discussing treatment.

Experts caution, however, that the treatment — a more targeted way of destroying cancerous cells than conventional radiation using photon beams —only offers extra benefits in a small minority of cancer cases. They declined to comment on King’s case but said the type of brain cancer he has —medulloblastoma — is not usually suited to proton beam treatment.

“Dose for dose, proton beam therapy is actually no more effective on the cancer cells than conventional radiotherapy,” said Adrian Crellin, a consultant clinical oncologist and the UK government’s national clinical lead in proton beam therapy.

The treatment uses beams of protons rather than X-rays or photons and targets them at the cancerous cells to kill them. The protons are directed at a tumour more precisely than X-rays and unlike in conventional radiotherapy, the proton beams stop once they hit the target rather than continuing through the body — making them less likely to harm healthy tissue.

Simon Jolly, a lecturer in accelerator physics at University College London (UCL), said these key features of the proton beam make it highly suited to some hard-to-reach tumours, or tumours growing very close to other key organs that could be badly affected by radiation, such as the brain stem or spinal cord.

“What you’re trying to do is deliver the beam in a targeted way,” Jolly said. “The key advantage with the proton is that it goes in and then stops. And it dumps most of its energy, doing most of its damage, at the end of its path. So not only are you doing less damage on the way in, but it also means that if there are sensitive areas, you will not damage them.”

But proton beam therapy is not recommended for medulloblastoma because the treatment should not be targeted to the tumour only.
“There are some tumours that require radiotherapy to the whole brain and whole spinal cord,” said Yen-Ching Chang, a specialist in paediatric radiotherapy at UCL.

Britain’s department of health says that since April 2018, proton beam therapy will be offered to up to 1,500 cancer patients at two major hospitals — UCL in London and the Christie cancer hospital in the northern hub city of Manchester.

Until then, British cancer patients who doctors believe would benefit from the treatment will continue to be sent overseas — either to the US or Switzerland — for treatment paid for by the taxpayer-funded National Health Service (NHS), the experts said.    Reuters