Are the conformality constraints still important when organ at risk constraints are met for lung SBRT?

Conformality constraints required in some lung SBRT clinical trials served as useful treatment planning guides that obliged attention to reducing the exposure of adjacent normal lung tissue to high dose.

I am unaware of data specifically validating any of the indices mentioned in the question as a predictor of lung toxicity (if anyone knows of such data, please point it out!), but it should be appreciated that almost all normal tissue dose metrics in any given organ are inter-related to some extent. A higher R50 would likely go with a higher mean lung dose, eg. The AAPM has organized a working group that has scanned the published literature to try to make some sense of dose metrics that predict the risk of normal tissue toxicity after SBRT t...

Maybe we think that *every single plan* we've ever been a part of has been "optimally optimized" where no further dosimetric improvements can be made. In practice however there is always room for dosimetric improvements. Always. In his classic IMRT paper (which should be required reading for every rad onc), Webb writes:

"Something that is optimum cannot be bettered by definition. Therefore the optimum plan is the best that could ever be obtained for treating a particular patient with a particular external shape, location of disease and arrangement of internal organs. I propose the view that this optimum plan is unachievable and that in practice this does not matter. To arrive at the optimum plan one would have to investigate the use of: (i) ...