Here, high-resolution transmission electron microscopy (TEM) with gold-labeled pKu70 and 53BP1 [29, 30] was used to determine the suitability of this analysis for assessing individual PBL radiation sensitivity in patients with different tumor entities (head and neck or rectal cancers), isodose volumes, irradiation techniques (intensity modulated radiotherapy, IMRT or 3D-conformal RT, 3D-CRT), and treatment approaches (RT or RCT). Here, TP53BP1 is linked to rectal cancer.