It feels as though every new idea I have has already been done by someone else or a government agency. My initial idea was to use manifolds to determine tissue structure and calculate the probability of irradiation. Turns out, the International Commission on Radiological Protection (ICRP) has already calculated out the risk factors for different types of tissues. The unit of Sieverts is an actual measure of health effect on different types of tissues. The information about the effective radiation dosage (Sieverts) is found easily on the internet.
Effective radiation dosage gives a good general idea about the possibility of adverse effects caused by radiation with different types of scans. The issue is that nature of each scan differ from each other and the risk changes per individual. Generally, Computed Tomography (CT) and x-ray will affect the superficial parts of your body: the skin and some tissue below that. Radioisotopes are more spread around the interior of the body because it is injected intravenously.
You would think that Radioisotopes would be more harmful because it is entering the interior of the body where everything is more vulnerable. It is true in some aspects, but the radioisotopes will be in your blood flow for a little while before it is taken up by the organs. The main source of irradiation from radioisotopes is where they accumulate. Eventually your body will remove the radioisotopes through the digestive and urinary systems. Your digestive and urinary systems are actually very hardy and already receive damage from stomach acids and bodily wastes. There might be some lingering fears about radioisotopes going to sensitive areas of the body like the brain. The thing is, radionuclides are different from CT and x-ray because it gives off radiation over time, unlike the direct hit from CT. So for the initial hour the radionuclides are in your body, the amount of radiation absorbed is actually small and generally insignificant. Assuming that your body takes about 6-10 hours to process and excrete wastes, the radioisotope is in your blood stream (entire body) for about an hour, where it will then decrease as it is taken up by the targeted organ for while and then excreted in another few hours. The amount of concentration when it is in the blood stream is minimal and it is only when radionuclides enters the targeted organ or digestive/urinary systems that there is enough concentration and radiation to be significant.
Aside from all that technical stuff, I got to visit Banner's Radiation Oncology. Oncology is involved with treatment of cancer and they use radiation to solve the problems. I was shown around by Dr. Hanny, Dr. Deng, and Ms. Mickie, medical physicists who work in Radiation Oncology. A big part of cancer treatment in Radiation Oncology is Stereotatic Body Radiation Therapy (SBRT). This is basically surgery using radiation.
In SBRT, the people are using linear accelerators to slam electrons/protons into your body. The Mayo Clinic in Phoenix is currently constructing their proton accelerator building (sidenote). In x-ray and CT, most of the radiation is absorbed by the skin and superficial tissues. By changing the x-ray used, the payload can be deposited deeper into the body. Although the skin will absorb a chunk of it, most will go through towards the target. Then it is the precise obliteration of the tumor (I am romanticizing this too much I think). To be more in-depth, it is not the radiation that is actually destroying the cells. The electrons/protons shot from the linear accelerator (nearly at the speed of light), will interact with the atoms to generate x-rays. The x-rays, with oxygen (O2) and water (H2O), will generate a hydroxyl radical (OH free radical). The hydroxyl radical is highly attracted to DNA, which will then disrupt the structure of the DNA. Because SBRT is 7000 times stronger than CT, destruction is assured (I am totally blowing this out of proportion).
Hydroxyl Radical damage to Guanine :
Linear Accelerator :
The planning of SBRT to irradiate a brain tumor. The physicists need to construct a plan prior to irradiation. They will try to spread out the dosage over a large area of skin. This is because several shots of 7000rem will destroy the skin as well. So if you spread it out over a large area, the dose given to the skin is much lower. Sometimes hitting sensitive structures is inevitable, and the doctors will have to decide the tradeoff. There is always a tradeoff in SBRT, because there is a splash spreading effect of radiation as well. Basically, in an exaggerated situation (probably unlikely but this is what it is like), the doctor has to decide to irradiate your eyes, giving you a 25% chance of getting cataracts, or your Cochlea in your ear, which might lead to hearing loss. The program (the amount of programming that goes into medical programs is so impressive) will do a hundred iterations after the physicist puts in base values. Then there is the fine tuning of the plan where the doctor decides if the values are acceptable.
Cancer cells have a different radiation toleration compared to regular cells because of their irregular growth and structure. This gives a small gap where you can destroy a major portion of the cancer cells at the cost of some normal cells :
Please feel free to ask lots of questions. After 2 hours in Radiation Oncology I ran out of questions to ask and I felt completely incompetent. Asking good questions is a very difficult skill to master.
Until Next Time!
-Phillip Yang
I honestly never thought that particle accelerators could be used to benefit in the field of cancer treatment. Also, I agree, asking good questions is hard haha but I'm gonna give it a shot. How do you think the tradeoffs you mentioned will delay the mainstream application of this new technology, and for how long?
ReplyDeleteHi Pranav! At Banner, stereostatic body radiation therapy is a mainstream technology, and is commonly used. The tradeoffs are ultimately up to the doctor to decide.I think they have 3 linear accelerator machines at Banner.
DeleteHi Phillip! The discussion about the radioisotopes was very fascinating and I have a few questions that you may or may not be able to answer. Since the radioisotopes are injected intravenously, is there a particular vein it is injected into? Also, how do the radioisotopes know which organ is the "targeted organ"? Do you know if the SBRT is used for all/ most cancers or only for brain cancer? Sorry for all the questions. This topic is really interesting and I would just like to learn more.
ReplyDeleteHello Rachael, ask as many questions as you want, I'm fine with all of them! I think the standard for intravenous injections is a surface vein that is not too small that it has low circulation. The vein that most intravenous injections use is the standard one in the pit of your elbow.
DeleteRadionuclides are used in functional scanning. So it uses the organ's function to take an image of it. For example, your thyroid uses Iodine, so by injecting iodine into the body, it will eventually appear in the thyroid. If you attach Technesium-99 to calcium, it will eventually lead to the bones. If you use FDG (F-18 on Glucose), you can tell which part of the body is using a large amount of glucose. Radionuclides is probably not the best term (sorry) because it is basically a radioactive version of an element. What they use in scanning is a Radiopharmaceutical. A Radiopharmaceutical is a radioactive tracer attached onto a drug or molecule which helps direct the tracer to the target. For brachytherapy (Y-90, Radium-192, sealed radiation therapy), the operator can inject it into the body using a catheter. They can follow the artery to a certain spot and then leave the radioactive source there to irradiate the area.
SBRT is used for multiple types of cancers. From what I saw in Radiation Oncology, it is used for brain cancer, breast cancer, leukemia, lung cancer. For SBRT in leukemia, they irradiate the entire body over a few days until 3 days before the operation. This kills off all the red marrow in the body. The patient can usually last a week without new blood cells before they receive severe adverse symptoms. I think it comes down to the tradeoffs and what decision the doctor is going to make.
1 error. Brachytherapy does not always have to inject. If you injected Radium-192, that would be really really bad. You can leave the catheter inside the body and have the radium in the tip of the catheter.
DeleteHi Phillip! So do cancer cells have a much higher radiation tolerance than regular cells? Also, what parts of the body can you use this "surgery by radiation" on? Since you said that they avoid hitting sensitive areas like the brain, I am assuming that they would not use this for brain tumors, maybe? And if they do, how do they control it? Sorry that was an overload of questions but this is a lot of interesting stuff!!
ReplyDeleteHi Charlotte! Actually it's the opposite where cancer cells are more weaker than normal cells. They have a thing called heat therapy where you can heat up the cancer cells which will denature a large amount of things rendering it useless. This is also because cancer cells have a lower toleration for heat.
DeleteActually, radiosurgery is used a lot for brain surgery (you can see in picture 3). Parts of brain are not as important and will be traded off for destroying the brain tumor. A brain tumor is usually more lethal than some radiation. The issue comes up when certain parts of the brain or face are in the path of the radiation. I don't know the exact names for the locations, but they are around the forward and lower to center part of the brain. Also hitting the eyes is dangerous as well. After you reach a certain level of exposure, cataracts will form. I don't think there is any particular difference in the brain tumor removal. There are different values for the parts of the brain, but the doctor will decide the tradeoff. The most control that they can do is make sure the path of radiation will not hit the sensitive parts.