Question: what is the function/use of the linear accelerator?

Rob Brass answered on 13 Jun 2016:

Do you mean how does it work or how do we use it? I’ll answer both anyway 🙂

How we use it:
The patient is CT scanned and a ‘treatment plan’ is made using special software. the treatment plan is a computer file that tells the machine what size radiation beam to deliver, from what angle, how much radiation to deliver, etc. The patient then shows up for treatment (given in daily doses over several weeks), their plan is loaded and they’re setup on the treatment couch (a flat, hard bed that we can move and rotate) in the same position as when they were scanned. This setup is important as it’s what we based the plan on! For our simple plans the linac (linear accelerator) will then rotate to the correct angle and it will set the size of the beam using heavy metal ‘Jaws’ inside the ‘head’ of the machine. For slightly more complicated plans we use something called MLCs (multi-leaf collimators). These are a series of thin metal strips that we can use to shape the beam to match the shape of the tumour, see the pic in the link:

For our most complicated treatment plans the linac rotates around the patient while delivering radiation. The MLCs in this case are always moving, as the shape of the tumour in the view of the beam will change. By delivering like this we can spread out the dose to the healthy tissues while still giving a high dose to the tumour.

How it works:
This can get a bit complicated, I didnt understand it all until I was doing my masters degree! I’ll try to keep it as simple as I can! There are 2 bits at the start of the process, one of them creates microwaves (called a magnetron or klystron – cool names i know 🙂 ) and the other creates electrons (called the electron gun). Both of these are fed into a metal tube we call a ‘wave guide’. the microwaves push the electrons along the wave guide, speeding them up (imagine a surfer on a wave!) and so increasing their energy. At the end of the tube the electrons are bent by 90 degrees using magnets so that they’re now travelling towards the patient. They then hit a metal block and give up their energy as photons (little packets of energy). After this we can use the jaws and MLCs I mentioned before to shape the beam for our patient.

How was that? If anythings unclear just comment again and I’ll try again! 🙂

Thanks!