Bobby Koneru, Vice Chairman of The American Radium Society, Founder and President of POG, shared a post on LinkedIn:
“The Slow Theft
For two decades, we’ve been irradiating healthy brain we didn’t need to.
The standard glioblastoma margin (2 centimeters beyond the tumor edge) was never based on where tumors actually recur.
It was based on uncertainty. On “what if we miss.”
Here’s what we knew the whole time:
- 80% of glioblastomas recur inside the original high-dose volume regardless of how large you draw the margin.
- Larger margins were never saving lives. They were buying peace of mind at the cost of cognition.
- GBM resection cavities don’t stay still during a 6-week treatment course.
- Most shrink by up to 80%. Which means by week 5, you’re treating a volume built around a cavity that no longer exists.
- About 20% expand. Without daily imaging, you’d never know. Treatment delivered. Tumor uncovered.
A trial called United just published its dosimetric data.
The Sunnybrook team Arjun Sahgal, Thomas Mann, Mark Ruschin and colleagues at Odette Cancer Center reduced the CTV margin from 2 centimeters to 5 millimeters using weekly adaptive replanning on a 1.5T MR-Linac.
The results, just published in IJROBP (Mann et al., 2026), show something clean:
- The adapted small-margin plans maintained target coverage at or above the minimum threshold across all 6 weeks of treatment.
- The conventional wide-margin plans?
More variable. More drift. More weeks where coverage slipped toward and sometimes below that red line. - Week 6 conventional coverage outliers reached 36.6%.
The adapted plans held.
Same disease control intent. Fraction of the irradiated brain volume.
This isn’t a theoretical benefit.
The difference between 41 extra cubic centimeters of brain receiving full therapeutic dose and not receiving it over 30 fractions is a quality of life conversation patients deserve to have.
The clinical outcomes data from United is coming.
Kudos to the Sunnybrook team for doing the methodical work to get us there.
Watch this trial.”
Other articles featuring Bobby Koneru on OncoDaily.