Recently, some clever people have managed to combine a radiotherapy treatment device (a Linac) with a Magnetic Resonance imaging device (MR). In addition, the information obtained is not real-time, which in a constantly moving patient provides you with outdated information as soon as you see it. The image of hitting a pinata blindfolded comes to mind, but we are slightly better than that, and making the pinata bigger (i.e. So most of the time when treating a patient we can't easily see what we are treating. But, X-rays are limited because only bony anatomy can be visualised reliably and soft tissue only in some rare cases. X-ray based computed tomography (CT) is used to provide geometrically and physically (electron density) accurate information. With great imaging, we can see better, aim better, treat better and monitor biological changes.īefore MR-Linacs, images were taken using X-rays or MegaVoltage beams. Great imaging tells us what is going on as well. This allows smaller margins, but there is more to imaging than just making visible the internal anatomy. devices that allow us to observe the patient externally and internally and make sure that we aim at the correct thing. We therefore want to increase the volume but not too much ideally we do not need to have margins at all.Įnter in-treatment imaging, i.e. We treat a volume larger than intended and manage any increase in complications, the larger the volume treated the worse and more likely the complications. We respond to this by choosing the lesser of two evils. The intended target will always receive less dose (compromising the curability) and whatever we did not aim for gets a higher than intended dose (increasing treatment complications). Since our target moves, we create a double jeopardy. So we solve our equations and deliver our beam: E pur si muove – And yet, it moves! They move (voluntarily and involuntarily), they breathe, their hearts beat and their digestive system works away (Don’t ask!). We have to deliver these beams, be it X-rays, protons, Helium nuclei, Carbon ions, or Higgs bosons (I wish) to a living breathing patient. The results of solving these equations can be coupled to large machines, which generate beams containing protons or other heavy charged particles, which make these solutions more forgiving.Īll very tidy in theory, but this is real life. We do this by getting as close as we can to solving insoluble multi-parametric equations. Modern radiotherapy concentrates radiation coming from different angles to shape the dose to match the shape of the tumour. We go to extraordinary lengths to minimise the amount of normal tissue that is irradiated, and we are pretty good at it. Radiotherapy therefore damage normal cells as well as cancer cells, which causes side effects, which reduce quality of life for our patients. The goal of radiation therapy is to destroy tumour cells, but we cannot target tumour cells alone. Today, these words could be used to under-pin the value of MR-Linacs in radiotherapy.įirst, let us define the problem. Galileo is said to have muttered ‘E pur, si muove!’ – ‘And yet, it moves’ as he left the courtroom in which he had been forced to concede that the sun moved round a fixed earth.
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