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. This week, we continue our discussion about the fundamentals of Radiation Oncology with our guest, Dr. Evan Osmundson.
*We hear the terms “hypo-fractioned” and “hyper-fractionated” radiation. What do those mean?
- Fractionation, that is breaking up the total dose of radiation into smaller ones, has allowed patients to tolerate the radiation better. The repeat exposure allows the healthy tissue to repair, whereas the tumor is not able to heal as well
- Standard fractionation involves keeping the maximum dose per session at 1.8-2Gy/fraction.
- Hyper-fractionation is when a patient gets multiple doses per day, each less than 2Gy. This is important in small cell lung cancer, where the standard dose of radiation is 1.5Gy twice daily
- Hypo-fractionation os when larger doses are given in each session, typically larger than 2.5-3Gy, often 4-5Gy per fraction. This is analogous to SBRT.
*With regards to SBRT, how do you determine the number of sessions?
- Typically 3-5 sessions, and this is based on data run through their computer algorithm that allows the dose to be tumoricidal.
- More sessions (more likely 5 sessions) if central tumor (<2cm central proximal bronchial tree) or ultra-central tumor (directly abutting bronchial tree/major vessel) or abutting the chest well. Poor outcomes in some studies with fewer sessions; 5 sessions seem to work well in central tumors, based on recent data.
- Logistically speaking, five sessions is also typically the maximum that insurance will pay for.
*What’s the max size of the tumor that is amenable to SBRT?
- Most clinical trials have limited size to 5cm or less, but he has done SBRT to larger tumors. This is a case-by-case basis.
* How do you calculate the duration of treatment when we are going to do concurrent chemo-radiation?
- Treatment is usually 5 days a week, with the weekends off for patients
- In NSCLC, total 60Gy appears to be the standard of care, based on RTOG 0617 study. (J Clin Oncol 2020 Mar 1;38(7):706-714. doi: 10.1200/JCO.19.01162. Epub 2019 Dec 16.); practically this means about 6 weeks of treatment.
- In SCLC, Target 45Gy broken up into 1.5Gy TWICE daily OR 66Gy broken up into 2Gy ONCE daily is the standard of care based on CONVERT trial (Lancet Oncol. 2017 Aug;18(8):1116-1125. doi: 10.1016/S1470-2045(17)30318-2. Epub 2017 Jun 20.)
* What is your guidance to avoid brain toxicity, for instance with using SRS to the brain for a brain met?
- There is a risk of brain necrosis from the synergism between certain chemotherapies/targeted agents that penetrate the blood-brain barrier with SRS that can cause radiation necrosis to the brain. This is particularly an issue with TKIs, such as osimertinib. Dr. Osmundson recommends holding TKIs about 5-7 days, if possible.
*What is proton therapy and how does it differ than “traditional” radiation therapy?
- With x-rays/photon therapy, the beam is attenuated and there is an exit dose that can affect the neighboring tissues.
- With proton beams, there is a “Bragg-Peak” effect, whereby you can specify how deep you want to radiation to deposit with little exit dose.
- Per Dr. Osmundson, we are not currently in a position to recommend proton therapy AT THIS TIME, but this may be changing. Research is being done to better be able to maneuver the beam angles.
- Proton therapy is also very expensive at this time
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!
Please visit our website (TheFellowOnCall.com) for more information
Twitter: @TheFellowOnCall
Instagram: @TheFellowOnCall
Listen in on: Apple Podcast, Spotify, and Google Podcast