There is at least one more radioactive point on the map. You may have been there and been exposed to radiation.
No, I'm not talking about the cave. But now I see that there are three radioactive places: directly near the radioactive capsule, in the second river, and near the gravel heap next to the TR_1.
And no, you're safe inside the cave until you find [spoilers].
You can use the dosimeter to find radiation.