Is there a volume or size criteria where you feel that standard doses for palliative radiation (8Gy/1fx-30Gy/10fx) are not effective?

At the risk of running off the mathematical rails, I thought about this question from a completely non-clinical viewpoint (from a clinical viewpoint, yes, I would probably use a bit more than 30/10 for a big 10 cm mass).

Here are a few assumptions. First, the D-sub-zero (D0) for many tumor systems h...