That's 100 mSv acute. Did he get it acutely (i.e. in a day or two) or over years? If acute then yes, the measurable increment over a background 40% lifetime ris

That's 100 mSv acute. Did he get it acutely (i.e. in a day or two) or over years? If acute then yes, the measurable increment over a background 40% lifetime risk could be due to Fukushima. So then the question is what's the increment? Let's estimate that it's 1% (based on the noisy data at these still quite low doses). In that case, there is a 1 in 40 chance that his cancer death in 2016 was due to Fukushima in 2011. It it wasn't acute and accumulated over >1 year, then there's a ~0% chance it was from Fukushima radiation.