Wednesday, October 17, 2012

Over the rainbow

I find it curious that while it was one slice of the electromagnetic spectrum (ultraviolet radiation) that likely got me into trouble with cancer in the first place, it’s another, closely related slice (x-ray radiation) that’s now being used to try to get me out of it.

This is the sort of random thought that comes to someone while their head is riveted to the table during a daily radiation treatment. They may immobilize my brain, but they can’t stop me from using it. I only have two more sessions to go, by the way. I’m definitely wearing out from the combined effects of brain x-rays and ipi, but am beginning to see the visible radiation at the end of the tunnel.
I figure a speck of light is better than an onrushing train.

Forgive me for the science lesson, but I'd like to elaborate on this business about the electromagnetic spectrum. It's actually pretty interesting, if you can hang in there with me as I explain its application in my life.

UV light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays--in the range of 10 to 400 nanometers (nm). It's called ultraviolet because this part of the spectrum consists of electromagnetic waves with frequencies only a little higher than those we perceive as the color violet. You and I can't see these frequences, but a number of insects and birds can. Think about that for a moment.

Click on this chart to get a better view of how
closely related the various forms of EM energy
mentioned in this post really are.
As anyone who's ever had a sunburn knows, UV light is found in sunlight. It's also emitted by those black lights many of us hung in our dorm rooms back in the '70s. Most ultraviolet radiation is classified as nonionizing, making it relatively harmless to humans. It does possess some of the dangerous biological features of ionizing radiation, however, and is capable of doing far more damage to molecules in biological systems than is accounted for by simple heating effects.

Sunburn, for example, is caused by UV light’s power to alter chemical bonds in molecules, even without having enough energy to ionize atoms. This is why the UV irradiation present in sunlight is considered a human carcinogen and its toxic effects are a major concern for human health. Spend enough time unprotected in the sun or on a tanning bed and you’re practically guaranteed a case of skin cancer.

X-radiation, on the other hand, has a wavelength in the range of 0.01 to 10 nm, which allows it to penetrate some solids and liquids. Without x-rays there would be no diagnostic radiography or radiotherapy—nor, for that matter, any Diagnostic Imaging magazine, and then where would my career have gone?

Radiotherapy uses higher energy levels than the radiation used in, say, a CT scan. It’s commonly used in cancer patients because of its ability to control cell growth. Ionizing radiation works by damaging the DNA of exposed tissue leading to cellular death. To spare normal tissues or, as in my case, brain structures, shaped radiation beams are aimed from several angles of exposure to intersect at the region of interest, providing a much larger dose there than in the surrounding tissue.

The reason treatment of my brain has gone on so long (four weeks) is because of the concept of fractionation. The total radiation dose I was prescribed has been fractionated (spread out over time) to allow normal cells time to recover, while tumor cells are generally less efficient in repair between fractions.

Fractionation also allows tumor cells that were in a relatively radioresistant phase of the cell cycle during one treatment to cycle into a sensitive phase of the cycle before the next fraction is given. Similarly, cancer cells that were chronically or acutely hypoxic (and therefore more radioresistant) may reoxygenate between fractions, improving the tumor cell kill.

OK. Got all that?

If there's a point to what I’ve written here it’s that there’s a fine line between the electromagnetic energy that our eyes perceive as light, that falls on our skin and causes cancer, and that penetrates a skull as thick as mine and kills cancer cells. These forms of energy differ only in their wavelengths. That which can bring us great pleasure, great heartache and ultimately great hope are arrayed along a spectrum like colors of a rainbow. Just thinking about this boggles what little of the mind I have left.

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