I have breast cancer and I’m starting radiation tomorrow. I understand that it’s supposed to reduce the risk of reoccurrence and that it is destroying cells. But how? Which cells are affected? Why will it make me tired?
In: Biology
Quick recap on what ionizing radiation does. When electrons absorb an electromagnetic wave, they move up into a higher energy state, which is kind of like a higher “orbit” around the nucleus of its atom. Ionizing radiation gives electrons so much energy that they can fly off the atom entirely. Atoms bond into molecules by sharing and trading electrons, so if you suddenly knock an electron off, it can really screw up that molecule. Plus, atoms really want to be electrically neutral, so if an atom loses an electron it will try to take one from another atom and end up either ripping the electron away (screwing up that molecule) or bonding into the molecule (also screwing it up). Other forms of ionizing radiation are alpha particles (which are basically helium nuclei going *really* damn fast) and beta particles (which are electrons and positrons – which are the antimatter version of electrons, exactly the same but with the opposite electric charge – going really damn fast).
DNA is *really* sensitive to these sorts of changes because it’s just such a huge molecule. There are many opportunities to absorb radiation, and even small changes in the bonds between atoms can really screw up the whole molecule. This is why ionizing radiation is dangerous and can lead to cancer – your DNA gets damaged so that the cell’s instructions on when to die and how often to reproduce get messed up, so it doesn’t die and reproduces way too much. That’s very unusual, though. Most of the time, damage to DNA either isn’t enough to do anything at all; or, the damage is so severe that the cell can’t function and dies; or, various safety features built into your DNA cause the cell to notice that it’s damaged and it self-destructs or gets killed by an immune cell. It’s rare that the damage is *just right* to cause cancer. Unfortunately for us, we have a *lot* of cells so even if it’s rare, there are so many opportunities for it to happen that we end up with cancer.
What radiation therapy is trying to do, then, is apply a high dose of radiation targeting only the cancerous cells and tear up their DNA so much that they can’t function anymore and just die. Nothing is perfect, of course, and the radiation can and probably will damage nearby healthy cells. It will even increase the risk of cancer in those cells. But think about it this way: what’s the worst thing that could happen, you get cancer next to your cancer? The benefit – hopefully killing off the existing cancerous tissue – is worth the risk. And, the radiation therapy will be as targeted as possible so that most of the affected cells are the cancerous cells and the surrounding healthy tissue won’t be too affected.
There are a few ways of targeting the tissue. One way is to create a sort of “laser” of positron radiation and aim it at the cancer. The positrons will have enough energy to penetrate into your body to reach the cancer. From there, the positrons will combine and annihilate with electrons (as matter and antimatter do), which creates some high energy gamma rays. Between the positrons annihilating electrons and the gamma rays knocking them around, the DNA should get properly shredded and the cancer cells will die. They may insert a tiny radioactive pellet that spits out alpha rays. Alpha rays will knock atoms and electrons around around, but they can’t penetrate through a thick sheet of paper, much less deeply into your body. That’s why they have to surgically insert the source into the middle of the tumor; but, since it doesn’t penetrate very far, it won’t affect tissue away from the tumor. They may also just use a beam of X-rays or gamma rays, pointed at the cancer.
It makes you tired because it’s killing off a bunch of cells, both healthy and unhealthy. Your body has to repair the damage and clean up the dead tissue, which takes energy just like any other injury. Depending on where the cancer is, it could be really messing up the function of an important organ which needs to be repaired. Again, the damage is worth it because you’re killing off much more dangerous cancer. Regardless, fixing that requires a lot of effort from your body.
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