The second thing is with the cobalt 60, you could get enough of it in terms of its activity to put in the machine so the output was high enough and so that you could do this. It was still there, but it was far less, and you’re putting the radiation much deeper. Cobalt 60 immediately sort of said, “Well, skin dose is going to be far less,” which it was clinically. As I say, it was the skin dose that limited the treatment. We had a whole suite here of ortho-voltage machines when I first came. ![]() ![]() It’s ortho-voltage therapy and ortho-voltage machines. Old x-ray machines in that range, a hundred to two hundred KEV were called ortho- voltage, and you’ll see that term. Radiation reactions with cobalt 60 are much less than with the old x-ray machines. You put the radiation dose deeper into the body, and at the same time, you spare the skin. Then the dose, let’s say, ten centimeters could be 50 percent, 60. So the skin dose now is maybe 50 percent of what the maximum dose is, which is a half a centimeter. By the time you get to cobalt 60 energies, it takes about half a centimeter or so for the radiation dose to meet its maximum in the body. ![]() If you’re up in higher energy, you set electrons in motion with quite a lot of energy, which go in a forward direction and deposit their energy downstream. Now, if your X-rays are low energy, the electrons coming off are fairly low energy and they don’t go any distance. The other thing that happens when you go to the higher energies, when you deposit energy with a radiation beam in the patient, the X-rays interact, set in motion the electrons, and it’s the electrons that deposit the energy. The average energy was over a million volts, so that’s a big advantage. But cobalt 60 seemed to be promising, because it had a high-energy gamma ray coming out of it.
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