@Verus:
Let's see, an attack called Gamma Knife, named after a tool relying on radiation to destroy tissue. It leaves no marks on the body, which we could count against it being a slashing attack. It destroys insides, plural.
It hit Doflamingo in his chest, suggesting that at the very least, lungs and heart should have been affected.
So, I will now ask you how my interpretation requires any more of specific conditions to happen then yours.
Radiation affects the insides without leaving exterior wounds, and for that reason alone the name is relevant. It does not mean that the actual effects of radiation have to be applied. And if we have to get specific, radio knife is a technique used on one point in the body. That doesn't stand in line with several organs being affected, which I agree with. So you want the attack to do literally the same as the technique it was named after, but then it wouldn't make sense from what has been said.
And if he was hit anywhere, it was in the upper part of the abdomen. That is close to the chest of course, so that area may have been affected as well.
You could always argue that my interpretation requires the conditions of yours to not be there. But I ask you: Why not just give the benefit of the doubt? Imagine that radiation is not part of the attack. Until stated otherwise, that is the logical thing to expect, and why assume anything else when it doesn't make sense - it's not like you can prove me wrong.
In the end, your interpretation requires conditions not stated, while mine is based on the information we already have.