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.
Like his brothers, Robert and Renly, Stannis is a large man - tall, broad shouldered and sinewy. Jon Snow notes that Stannis towers over him. Stannis has dark blue eyes and a heavy brow. His head has only a fringe of black hair like the shadow of a crown, and he has a close-cropped beard across his large jaw. His face has a tightness to it like cured leather, and he has hollow cheeks, and thin, pale lips.