SRP Week 5 : Dosimetry

It seems hard to believe that it has been 5 weeks since our 2nd trimester has ended. I never thought I would say this, but I truly do sometimes miss school. I have been trying to continue learning by reading books and watching videos, but it feels so different from learning at school. I keep on expecting a period change to a new class or 5 minute breaks between every 50 minutes of reading to talk to somebody. It feels like I am studying 60+ hours for an exam that I am never going to take.

Recently I have been trying to relearn Chinese. I never really did try hard at Chinese School and my parents told me I would regret it when I was older. I truly feel the brunt of that pressure now (Feeling regret and I'm only 18 years old). I have tried to dabble a little in Japanese and Korean. My friend Sonya tells me that Japanese is easier than Korean and she occasionally helps me with my pronunciation. I walk around in my backyard saying "are" or "arigatou" or "wakaranai" and the occasional "cake" (Japanese "cake" is different from the English version where the "a" is more like an elongated "e". To me, it sounds like k-ee-k-i which is still probably wrong). Sonya says that, if I can learn the R/L sound, I can sound less foreign and possibly surprise someone.

I have been finishing up the second book that Mr. McCormick has given me. The title is Physics in Nuclear Medicine. I tried to learn by osmosis, but that never seems to work. Dr. Deng says that Radiobiology for the Radiologist is the so-called bible for the physicist and radiologists, I might check that book out sometime. The good thing about Physics in Nuclear Medicine (and probably any good medical book) is that it has a whole bibliography section after every chapter. I can look up the individual articles/books that it mentions and find even more details. It has has a whole 6 pages of tables, telling me the S-values of the entire human body for different radionuclides. That will help immensely in my calculations. It feels too basic if I do a Dosimetry of the epithelial tissue and internal organs with the given values by the book. I will probably also do a comparison of the histograms in the database with a scan from a Phantom (I need Mr. McCormick to do it because I can't touch the radionuclides in the hot lab).

I have a better understanding of why CT and x-ray have a growth in the amount of radiation dosage. In general for all medical imaging, the amount of exposure has decreased. The only exception is CT. The reason is that even with the amount of technological improvements, CT requires more dosage to improve image quality. So when they do a chest CT with contrast, they have to increase the dosage to have a good image of the blood vessels in the chest. There has been a big debate between using a chest CT with contrast or a VQ nuclear medicine scan. There are good arguments on both sides, but a big factor is that many doctors are comfortable with looking at CT-images. Even though a VQ can give around 90% probability and some additional details, doctors are afraid of the remaining 10% of uncertainty.

Although there is probably a 1-2 difference in mSv (milli Sievert) between CT and Radionuclides, it is the amount of CT's used by the hospital that makes the difference. Say a patient comes into the Emergency room with chest pain and wants to talk to a physician. By the time the patient talks to a physician, there is no more chest pain. The physician is pretty sure that the patient has no issues. But because the hospital does not want to be sued in case the patient does, the physician tells the patient to have a CT scan done. CT is so convenient, cheap, accurate, and efficient, physicians can tell patients to get one anytime. If a doctor doesn't have the images yet because of paperwork, he can just tell the patient to take another one and it will be done in 5 minutes.

Physics in Nuclear Medicine says that immediate radiation is much more damaging than prolonged radiation. I do not know if the effective radiation dose takes into account the different types of radiation, but if you compare the time difference between a Nuclear Medicine scan and a CT scan, the CT scan dose is probably quicker by factors of 10.

I am slowly getting the hang of the concept of radiation usage. By next week, I hope to have a calculated model of an internal organ, such as the stomach (that seems like an important organ to BASIS kids).

Mata ne! (See you later!)

Phillip Yang