Lung cancer is one of the most commonly diagnosed type of cancer and so it is fitting that we start the first of our disease-specific oncology series with this diagnosis. An important component of treatment in lung cancer (and many other cancers) is the use of radiation. Here, we discuss the fundamentals of Radiation Oncology with our guest, Dr. Evan Osmundson.
Basic vocabulary:
- Fraction/Fractionation: The total dose of radiation divided into smaller doses
- Grey: Unit of measure of radiation being delivered in each session
- Bragg-Peak effect: Specific to proton therapy (as opposed to photon therapy). It describes the sharp increase in concentration of the energy when hitting the tumor, while minimizing the effects to surrounding tissue.
- Radiosensitizing chemotherapy: small doses of chemotherapy used to make the cells more responsive to the deleterious effects of radiation
Fundamentals of radiation oncology:
*When we make a referral to RadOnc, what happens then?
- Send over any available imaging that is available
- Team reviews the imaging to ensure that staging is completed
- Simulation scan: Uses a CT scan to “simulate” the treatment; specifically map out the tumor and the surrounding organs/structures. Multidisciplinary team reviews the scan to maximize the dose to the tumor and minimizes damage to surrounding structures.
- Based on the scans, they test run the treatment on a model to ensure that the simulation on the computer is able to be replicated on a model.
- The above is why it can take a while for treatment planning to take place
*What sorts of imaging modalities are important to have for patients prior to getting to Rad Onc?
- Send prior CT imaging
- If planning for radiation to the brain, should get thin-sliced MRI w/ and w/o contrast
- If prostate cancer, also consider getting MRI
*Many patients express concern about the “mask fitting” - what is that?
- To ensure that the same dose of radiation is administered each time, it is important for the patient to remain very still and/or the same position every session. The mask is custom fit to ensure patient is in the correct position.
*How do you determine the “maximum dose” of radiation in the mediastinal area is?
- The maximum dose tolerance is dependent on the structure in question. A structure “in series” such as the bronchial tree would have profound effects if tissue is injured compared to lung parenchymal tissue (If you damage some, there is plenty more that is able to compensate)
- Always concern for spinal cord when radiating the mediastinum
*What are side effects you counsel patients on, specifically in thoracic radiation?
- Fatigue (usually not debilitating), radiation esophagitis, pericarditis (rare)
- Radiation pneumonitis (usually 6-8 weeks, but can be up to one year), presents with cough, shortness of breath; likelihood of this is dependent on duration of treatment, dose of radiation, location
A special thank you to our guest, Evan Osmundson, MD, PhD, Associate Professor in the Department of Radiation Oncology and serves as the Medical Director of Radiation Oncology at Vanderbilt University Medical Center in Nashville, TN!
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