Week 4: Who knew physics could be so cool

     This week, I met with Dr. John Ng, a radiation oncologist who has a specialty in breast cancer. I went through a unmethodical way of how a patient receives radiation after diagnosis. We met with his first patient who had received radiation to the left breast following a breast cancer diagnosis. Dr. Ng stressed to the importance of using a moisturizing cream to help retain moisture after the radiation while the skin is still sensitive. Dr. Ng already knew that I had already done plenty of clinical follow-ups and suggested I see how they create treatment plans for patients about to undergo radiation. I was taken to a room, similar to a reading room used by radiologists, where the techs create simulations using tangent fields to create treatment plans form organs they specifically want to target. For example, women who undergo radiation to one breast often lay in the prone position using gravity to limit radiation to the heart and lungs. The techs come up with a plane for radiation dose, "266 Gy per fraction to 100% of point dose at tangent calculation point for 16 fractions." Gy or gray is the unit ionizing radiation dose. The techs contour organs close by to receive little dose based on critical dose constraints. Once the doctor approves the plan, he writes the prescription for the dose.

     Next, I met with Dr. Sabass, a physicist, and an engineer who were doing a quality assurance check for radio surgery on the Novalis machine powered by True Beam. Radio surgery is the delivery of high dose radiation to treat brain disorders. They perform these quality assurance checks because the machine has to be highly selective and accurate, within a mm, when delivering such a high dose. The doctor, engineer, and physicist had to tell the machine to find the ISO center for a 3D calibration. The machine used infrared light that you can detect using non iphones, iphones have a infrared filter on them. The machine uses lasers and x-rays of phantoms to find the ISO center and correct any corrections made. After the calibration and assurance check, I witnessed my first patient receive radiation to the brain and lats. This was not radiosurgery but they use this machine for a lot of brain radiation. With brain radiation, there are constraints on the lens (max 7 Gy) and the eyes (mean , 35 Gy). The whole thing took less than 10 minutes. The techs, Julio and Kathy, that operate the machine in accordance with the doctor's prescription were extremely helpful in explain everything that was going on. They even showed me where they keep the molds made for each patient's face and neck that hold their heads in place.

     I then met with Dr. Michael Smith who helps with the simulations patients must undergo before receiving radiation better informing the treatment plan. On one patient with prostate cancer, they used a CT scanner to obtain cross sections of the pelvic anatomy to create a 3D model of the treatable area. The have these BBs they use to set the ISO center and once the scan is done, Dr. Smith sets new reference points to include most of the prostate. Finally, three small black dots were tattooed on the patient, one on each hip and one in the pubic region. These permanent tattoos that were the size of periods at the end of a sentence serve as landmarks for your upcoming radiation therapy. Also, they made molds filled with liquid styrofoam for his legs and feet to hold them in place during future bouts of radiation. The techs then take pictures of the patient's tattoos and body position as references.

     Finally, I went back to the Novalis machine and saw them perform radiosurgery on a 64 y.o. woman who had actually done it a few times. The techs double and triple checked the machine because she was about to receive 2000 cGy of radiation to the brain. To further break it down, she received 10 fractions of 717-960 Mu of radiation, which is a lot! She was a trooper throughout the whole thing which lasted about 45 minutes. The last patient I saw was receiving radiation to her right breast in the prone position as stated earlier. Overall, it was a very pleasant experience for me and I learned so much about physics, imaging, and radiation. Although this area is not my strong point, it definitely peaked my interest in radiation therapy.