Chapter 01: Radiation Therapy: A Brief History and Basic Principles


Chapter 01: Radiation Therapy: A Brief History and Basic Principles



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In this chapter, Dr. Almond discusses the physical principles that govern radiation therapy. He begins by describing x-ray tubes and how skin damage limited the dose of x-rays that a patient could receive. The chapter ends as Dr. Almond explains how this limitation led to the search for a higher energy alternative that would not share the same limitations.



Publication Date



The Making Cancer History® Voices Oral History Collection, The University of Texas MD Anderson Cancer Center


Houston, Texas

Topics Covered

The Interview Subject - Overview; Overview; Definitions, Explanations, Translations; MD Anderson History; MD Anderson Snapshot; Understanding Cancer, the History of Science, Cancer Research; The History of Health Care, Patient Care; Technology and R&D; Patients; Patients, Treatment, Survivors

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.


History of Science, Technology, and Medicine | Oncology | Oral History


James S. Olson, Ph.D.

One of the first things, I’m interested in the evolution of some of just the equipment. We start off with sort of the external beam equipment, and I guess also for my own knowledge, what the difference between a linear accelerator is and a Cyclotron, an x-ray machine, what the advantages or disadvantages of protons and neutrons, electrons, those technical kinds of questions. So we’ll start off with sort of the evolution of external beam.

Peter Almond, Ph.D.

As you know, x-rays were discovered by accident, but shortly after that, people started making x- ray tubes, which have electrons start the one side and go across and hit a target and produce the


James S. Olson, Ph.D.


Is this a cathode?

Peter Almond, Ph.D.

Yes, but within the X-ray tube, you have to apply a high voltage across the tube to accelerate the electrons to hit the target and then produce the X-rays. With development, you can get the voltage across the tube up to about two hundred, three hundred thousand volts, and the higher the voltage, the faster the electrons go and the higher the X-rays that come out. Now, the reason you want high-energy X-rays is that the higher the energy, the more they penetrate into the body. In the early days when it was very low voltage on the tubes, the X-rays produced essentially would go into the body and would penetrate, but they would very rapidly lose their intensity. So you couldn’t put much radiation dose deep in the body. All of it would be at the surface.

James S. Olson, Ph.D.

Therefore there would be more damage at surface tissues?

Peter Almond, Ph.D.

Of course, if the tumor was there, that’s where you want to put the radiation energy, but you had to go through the surface and then the surface got a higher energy.

In those days, radiation therapy was limited by the skin dose, and people got arethemas [?] and skin reactions very, very severe in those days of radiation therapy. It was all limited by the skin reactions, I mean how much dose you could put it at because the radiation went through. But clearly so, if you could get more radiation going deeper and deeper, then you could spare the skin. But up to about two hundred, three hundred thousand electron volts was about on a regular basis what you could do with regular X-rays tubes.

Now, there were some special tubes made that went up higher. One or two were built, but they were just too difficult and large and cumbersome. But for the normal sort of X-rays used in treatment, two hundred and fifty to three hundred thousand electron volts were used. But even at that energy, you would get about 50 percent of the dose at about six or seven centimeters in. So you can see 100 percent on the surface and only 50 percent at six or seven centimeters. You were, again, really limited by how much dose the skin would tolerate.

Now, you could try using the radiation coming in from different directions to meet in the middle. You can do that, but even if you lost 50 percent by six or seven centimeters into the body, people are thicker than that, and so even using beams coming from different directions, it’s a problem.

So one really wanted to go in higher energy to get more penetration, but the X-ray machines for doing that just really cannot be built, at least not successfully and not on a regular basis. So that sort of took us up to about World War II when those machines were . . . and shortly thereafter with those kinds of energy.

It was people like [physicist Leonard G.] Grimmett and others who thought, Now if we could find a radioactive material that had a gamma ray which was the same as the x-rays but a much higher energy, maybe that can be used. Grimmett, before the war, had in England built a number of external treatment machines using radium, but radium had a lot of disadvantages. One, is it’s very expensive. Two, you had to get a lot of it to put into a unit to use for external beam, and they were never successful. They were extremely dangerous in many ways, too much radium around, and that didn’t seem to work.

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Chapter 01: Radiation Therapy: A Brief History and Basic Principles