Photons vs. Electrons

I just returned from my radiation treatment, and before I forget what I just learned, I thought I should get it all down. I had the first of my final 5 radiation treatments this morning, and it's a different ball game. The configuration of the linear accelerator is different - the bed is placed at a 90° angle to the machine now. While I waited and watched, the technicians inserted a metal plate into a frame in the machine, which would be placed nearly touching my skin.

The metal plate is a special alloy they had poured of lead, nickel, cadmium, and other metals into a mold, with an irregular hole cut into it matching the outline the doctor had drawn around my scar. The liquid alloy recipe is put together under a chemical hood, because the fumes from the cadmium they use is carcinogenic. The plate they made for me has an oval shaped cutout in the center about 2 inches wide and 7 inches long. Once the plate and frame had been snapped into place, I laid down on the table, and they moved the machine over me very closely, within a centimeter of my skin. The machine was nearly touching my chin. I was told I no longer had to hold my breath during the time the machine was sending out the radiation. Then they checked their measurements, left the room, and turned on the machine. This treatment was probably about 30 seconds long, and it was over.

Before I left, I asked Peggy why I no longer had to hold my breath to raise my chest away from my heart, and she explained that I'm now receiving a different type of radiation energy. Before, they were giving me photons. This new type of radiation energy is electrons. The difference is that the photons, having no mass, pass right on through the body, whereas the electrons, having mass, stop when they hit something in their path. The radiation using photons aims the rays from different angles to concentrate the beams toward the tumor site, therefore the machine is moved in a circular way around the body, giving dosages at precisely measured locations. What the doctor is looking to accomplish now is to treat the skin and scar area around the mastectomy. The radiation doesn't go further than a centimeter or so into the body, therefore it won't go in as far as the heart. The lead alloy mold assures that the energy goes only where they are aiming, preventing the rays from penetrating anything but the specific area they want to treat, within that oval area carved out in the lead plate.

I do have a science background, but mainly in Biology and Chemistry. Physics was not my strength, and I'm wishing now that I had paid more attention at the time. Who knew that later in life I would be trying to explain radiation energy pathways in a public forum. I hope what I wrote is clear.

PHOTO: The wishing well in our front garden in mid summer.