Treatment isodose distribution. Treatment isodose distribution for a patient with right TN, overlaid on a volumetric T2 image; the red oval outlines the trigeminal nerve, the green contour represents the 90% isodose line (81 Gy), the inner orange circle is the 50% isodose line (45 Gy), and the outer orange circle outlines the 13.3% isodose line (12 Gy).