Week 2 06/28/21

In the second week of the immersion program, I met up with my clinical mentor, Dr. Bradley Pua and I was shadowing him for the week. Dr. Pua's clinical interest is focused around minimal invasive thoracic procedures. As such, I was able to observe a CT-guided catheter ablation procedure for treating a patient with metastatic lung cancer. The catheter was inserted into the location of the tumour under repeated CT scan guidance. At the tip of the catheter, there was energy delivered to create a spherical or elliptical lesion zone to ablate the tumour. There are a few technologies that have been implemented for this purpose. Radio-frequency and microwave ablation (RFA and MWA, respectively) both use catheters which generates heat at the tips to burn off the local tissue. Cryoablation, on the other hand, utilizes a gas which rapidly expands at room temperature (e.g. Argon) to freeze and the thaw the tissue, usually with two consecutive cycles. Each technology comes with its own advantage and disadvantage. 

In this specific case, the patient's tumour in the lung was located close to the esophagus, and thus using RFA and MWA runs the risk of accidentally burning the esophagus and creating an ulcer. Cryoablation was therefore chosen and performed. In another case which I observed last week, RFA was chosen for its advantages, including faster action compared to MWA, a more clearly defined ablation zone, and overall a high success rate. Heat-based ablation techniques still face a limitation called the heat sink effect, which describes a phenomenon for when the tumour is located near a large blood vessel and the cooling effect from circulating blood limits the ablation volume around the probe. For cryoablation, the heat sink would not be a concern. Interestingly, sometimes a pre-ablation is performed for lung cancer cases to purposely induce bleeding and gather blood around the tumour. When the actual freeze-thaw cycle is performed, more tissue damage can be achieved. Other procedures which I witnessed this week include a collagen scaffold placement for treating abdomen/intestine fistula, transjugular liver biopsy, Y90 radiation for liver tumour embolization, and many more. In addition to shadowing Dr. Pua in the procedure rooms, I also spent a day in the hospital's ER radiology reading room, where I shadowed radiologists and fellows diagnosing X-ray, CT, MRI, and PET scans for patients who were visiting the emergency room.