 Consider the radiation treatment options for a patient with several brain metastases. We know that stereotactic radioseurgery, or SRS for short, better preserves cognitive function and quality of life without negatively impacting overall survival compared with whole brain radiotherapy, which exerts its toxic effects by damaging normal brain tissue. My question to you is how many brain metastases are you comfortable treating with the SRS before you recommend whole brain radiotherapy? Is your answer based on a maximum number of meds, say 10 to 15, on account of the time required for treatment planning and administration? Or is your answer based on a concern that in a patient with more than a few meds, treating only the visible tumors might allow for subsequent growth of microscopic deposits, which would require additional RT? Perhaps you are concerned that, over time, administering repeated rounds of SRS would expose normal brain tissue to as much radiation as is associated with a standard course of whole brain radiotherapy. The purpose of our study was to address that issue. How many brain metastases can be treated with SRS before the radiation dose delivered to normal brain tissue rivals that associated with standard whole brain radiotherapy? I'm Dr. Stuart Becker, Associate Professor of Radiation Oncology at the University of Maryland School of Medicine. To answer this question, we created a computer model of a brain then placed tumors of a typical distribution of sizes in random locations and simulated treatment with SRS until the mean brain dose reached three gray. That's the radiation dose delivered during a single fraction of standard course of whole brain radiotherapy, typically 30 gray over 10 daily fractions. We found that treating 10 to 13 tumors per day over 10 days would deliver the dose of radiation to healthy brain tissue typically associated with a standard course of whole brain radiotherapy. In clinical practice, treatment with SRS is often limited to patients with less than five brain metastases. However, our findings suggest that several times that number of lesions could be targeted while still minimizing the negative impacts on quality of life and neurocognition often associated with whole brain radiotherapy. In addition, with the advent of single isocenter multiple target SIMT, Linnac-based SRS, treatment times are considerably shorter and more convenient than a full course of brain radiation therapy. I encourage you to check out our manuscript to learn more. I hope you'll agree that our results are intriguing and warrant further validation in the clinical setting.