Stereotactic Radiosurgery

A parent in my class asked about the Gamma Knife (R) that Charlie Teo uses in his surgery and I thought I’d find out more about it.

Gamma radiation has a very low wavelength. Remember that in the electromagnetic spectrum, the lower the wavelength, the higher the energy associated with each photon (packet) of radiation.

This is my understanding of how the technique works.

Around 200 beams of gamma radiation are aimed at the tumour from different directions. Gamma radiation has such a low wavelength that it can pass through organic cells without affecting them, but this depends on the type of cells and the intensity of the radiation. The different beams pass through the rest of the body cells until they reach the tumour. When they join at the tumour site there is a very high intensity of radiation in a very small area. (Not only does each photon have high energy but there are many of them in one small space.)


Cancer cells are characterised by rapidly dividing and multiplying (unlike most of the rest of the cells in our body) and gamma radiation damages cells by breaking bonds in DNA, so cancer cells are damaged more by gamma radiation than the surrounding healthy cells are.

Differences between normal animal cells and cancerous cells. Image from Wikimedia commons. 

This looks like a great use of scientific knowledge and advances in technology to target cancer cells without damaging the rest of the body. I read that, because it is so specific, people who are operated on with this technique tend to recover far quicker than those receiving radiotherapy or being operated on by other surgical techniques.


Here are some links if you are interested:

Gamma Knife FAQs from University of Arkansas for Medical Sciences

Stereotactic radiotherapy for brain tumours (from Cancer Research UK). This includes a description of how people’s heads are immobilised for the surgery. As you can imagine, it is essential that the person stays completely still because the surgeon needs the radiation to get to exactly the right spot.

Radiation treatment on the old BBC GCSE Bitesize site.

Radiation and living cells, also from the BBC Bitesize site. This doesn’t give much of an explanation about how or why DNA is damaged but it does tell you about how alpha, beta and gamma radiation affect the body differently.

Information on the Elekta site about the Gamma Knife (R).

I say ‘plum’, you say ‘purple’.

The science of colour vision, and how our eyes and brains perceive colour, is fascinating.

Reblogged from MindShift, here’s a link to the top ten most popular educational videos on YouTube in 2013. Look at how many of them are about science! I haven’t watched them all, but I especially like number 4: Is Your Red The Same as My Red? from the Vsauce channel.

I worked with lasers in Birmingham University Chemistry Department, and from this and from my general scientific background I knew that we could take a single wavelength of visible light and say that it had a specific colour. But how do our eyes detect that colour? Inside our eyes, we humans don’t have specific detectors for each wavelength. Instead we have only three types of receptors (cones) each of which responds to a broad range of wavelengths, and two of which have ranges that overlap significantly. The combination of signals from each of these gives us a pattern which we then say is ‘red’ or ‘purple’ or ‘yellowy-orange’.

How do I know that your red is the same as my red? I don’t. Humans have quite wide variation in how their cones respond to the same wavelengths of light, and some women even have an extra sensor which gives them what is known as tetrachromatic vision (like some birds).

Our descriptions of colour seem to be limited by our language and our experiences, as discussed further in this post on Psych 256 (with references, which I haven’t provided here) and on a 2011 post on the blog EagerEyes.

There’s some very in-depth explanation of colour vision on the relevant Wikipedia page, and if you really want to study it further I highly recommend the Open University course SD329: Signals and Perception. The course materials are all available online. It is a Level 3 course, at an equivalent level to the final year of an undergraduate degree, and the OU has conveniently prepared a guide called ‘Are you ready for SD329?‘ (pdf file) for people to check if they have the appropriate background and experience.