Lack of late skin necrosis in man after high-dose irradiation using small field sizes: experiences of grid therapy. Out of a total of 437 patients with superior vena caval syndrome or advanced malignancy, given single-dose grid radiotherapy, four survived to 7 years. The dose to the skin under each of the 77 holes in the grid was approximately 58 Gy. The lack of skin necrosis in the total of 308 skin circles of 1 cm diameter among these survivors, compared with known necrosis rates in larger irradiated areas, implies that there is a marked field-size effect for late necrosis in small areas of irradiated skin. 