X-rays: It has been decided that I may be a... - Macular Society

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X-rays

ironbrain profile image
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It has been decided that I may be a candidate for stereotactic radiotherapy (SRT). It involves using a narrow beam of x-rays to kill off unwanted growth – good cells that also get damaged, it is claimed , can repair themselves.

Does anyone know where Retina Today gets the idea from that 100kV x-rays are "low voltage" x-rays? It's my understanding (as a physics graduate, you might say) that 24kV x-rays from old cathode ray tube colour televisions are already moderately hard.

retinatoday.com/2015/06/use...

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ironbrain
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11 Replies

Hi ironbrain

I read the article and found it interesting. Sorry, I cannot comment on the KW.

Personally, I am not sure I would go for the treatment unless the injections alone failed altogether. Are X-rays not to be kept to a minimum in general use? Perhaps more time is needed to assess the long-term effect. If you do decide to accept the treatment I would be interested to know how you are getting on with it. I wish you all the best.

ironbrain profile image
ironbrain in reply to

Hi ayayay

The Eylea has stopped the growth of blood vessels but some remain and there is some fluid still under the retina. My OCT last Thursday only showed a very marginal improvement over the one from 8 weeks before.

They tend not to like taking too many x-rays at the dentist, and they're just 70kV, I see. America seems to be taking a cautious approach. I can't help thinking it's a bit like some cancer treatments – first go in with the chemo, then finish the job off with radiation (although with CNV one continues to get the injections).

in reply toironbrain

Hi again

I went through breast cancer treatment 18 years ago and found the chemo far more distressing and debilitating than the radio therapy which followed, though the latter was given to me 5 days a week for for 5 weeks, so 25 doses in all. Towards the end of the course my skin started to break down. But of course, the eye treatment would be far less intense.

ironbrain profile image
ironbrain in reply to

I can understand your not wanting to undergo any more radiotherapy.

Not sure but I think they're confusing ( typo?) the kV high voltage power source of the cathode tube with the eV of the emitted x Ray itself? Wikipedia says 600eV soft x rays are low energy ( hard x rays go up to 100 KeV).

ironbrain profile image
ironbrain in reply to

600eV is 0.6keV, which are soft x-rays. The voltage is that between the cathode – from which electrons are emitted – and the (final) anode – the terminal which attracts the electrons – of the x-ray tube. Since all electrons have the same electic charge and the same mass, all electrons accelerated by the same voltage will have the same energy which is termed in electron-volts written in short as eV. Thus saying you're using an x-ray machine producing 100keV x-rays or a 100kV x-ray machine amounts to the same thing.

How efficient the target is, the thing the electrons hit to produce x-rays, is another matter. The best it will ever do is produce an x-ray of nearly the same energy as the electron hitting it. Most of the x-rays produced will be of a lower energy (which, in fact, equates to a lower frequency). Phosphor dots in the old CRT televisions probably didn't make very good x-ray targets; in an x-ray machine, I suspect you generally want to have a target that's as efficient as possible.

in reply toironbrain

😱 good job I'm not in charge of any medical device lol

SRT is a highly accurate treatment delivering the radiation at a controlled measure and within a margin of just 1mm. The strength of the radiation is carefully tailored to the individual need. Although I have not had the treatment is is used very successfully to “mop up” after more conventional treatments for eye cancer.

ironbrain profile image
ironbrain in reply to

I guess what worries me most is that it's shooting straight into the brain.

in reply toironbrain

I don't think so, it is very focussed and is used in difficult locations for precise effect.

eesnapal profile image
eesnapal

First please understand I sympathise.

The energy of the beam is not the issue.

The size of the dose imparted to the tissue is. While the beam is high energy it is very narrow - as a result the beam is aimed at the target tissue many 10s of times from different angles. The target tissue gets a large dose while the intervening tissue only a small one.

I am a lay person with a special interest in SRT. You are welcome to call but you must decide with your clinicians.

Yours

Steven

07711640567

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