To treat a pituitary tumor with radiation, doctors may use a variety of techniques depending on the size and location of the tumor. Conventional radiation covers a wide area in and around the tumor and is usually given daily for several weeks.
In the show, Stannis Baratheon dies under the sword of Jamie Lannister, wielded by a woman to fulfill a promise to Catelyn Stark, to avenge the death of Renly Baratheon. You can state he died of internal complications.
Oh well, the point of it was that Stannis has the only legitimate claim right now, because the Iron Throne belongs to House Baratheon and Tommen is not a Baratheon. In Robert's case, he took the Throne for House Baratheon by the right of conquest. From that moment, Targs has NO claim AT ALL for the Throne.