If you changed the magnetic field while these electrons were going around, you can induce them to a going energy, and you’re changing the field and their energies increase and the radius of their motion stays the same. It looks like a great big doughnut and was, in fact, called the doughnut. You have electrons going around in a circular motion inside a tube, which has got a vacuum in it. One of the first sort of possibilities for that was a device called the Betatrons, in which magnetic induction is used. Difficulty is getting the twenty million electrons for your x-ray machine. By the time the 50 percent dose is sixteen centimeters into the body, you can really start to put a lot of radiation dose into deep-seeded tumors, and you’re not limited by any skin reaction whatsoever. The maximum dose is about several centimeters into the body. If that was true, if you went from, say, 250,000 electron volts to one million electron volts, it could up now to ten, twenty million electron volts, really start, because now the skin dose really gets very, very low. So cobalt 60 looked like having a lot of advantages, and Grimmett and others in the development of the cobalt 60 immediately allowed you to do a lot of things you couldn’t do. There are various reasons you want to do that, but about a meter is about the optimum from the source, and you could get to that with cobalt 60. Because you had enough radiation, you could move the patient about eighty centimeters to a hundred centimeters from the source, so you had a nice little distance between the source and the patients. Treatment times were a reasonable length. Cobalt 60, you could get enough cobalt into the unit. You know, you didn’t get enough radium to really have the treatments over a short-enough 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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