Top Line: Let’s ponder once more the ideals of dose homogeneity in lung stereotactic body radiation (SBRT).
The Study: The most common way of looking at biologically effective dose (BED) for lung SBRT is to calculate the BED10 based on the prescription isodose encompassing the target. But some argue that higher doses within the target may further improve control. This Japanese retrospective study of over 300 patients with early-stage peripheral non-small cell lung cancer (NSCLC) compares two prescribing methods with the same prescription BED10 (50-60 Gy in 5 fractions) but with very different max doses (BEDmax) and PTV average doses (BEDavg). Between 2005 and 2011, they prescribed 50 Gy in 5 fractions to the PTV at the 80% isodose line (Dmax 62.5 Gy, BEDmax 140.6 Gy, BEDavg 119.5 Gy). Thereafter, they prescribed either 50-60 Gy in 5 fractions (depending on location) to the PTV at the 60% isodose line (Dmax 83.3 Gy/100 Gy, BEDmax 222 Gy/300Gy, BEDavg 155.5 Gy/187.5 Gy). While there are many potential biases when techniques change over time, patients who received a higher BEDmax and BEDavg had a significantly lower rate of 5-year local recurrence (1.3% vs 7.2%). Now, all of this should be viewed in the context of (1) conflicting data suggesting steep dose fall-off can actually compromise control and (2) ill-placed hot spots can kill.
TBL: The debate over allowable hot spot for lung SBRT continues, but it likely will turn out to be a nuanced answer based on target size and location. | Tateishi, Int J Radiat Oncol Biol Phys 2021