Field separation between lateral and anterior fields on a 6 MV linear accelerator

Field separations of 0, 2.5, 5, and 10 mm between lateral facial-cervical fields and anterior supraclavicular fields have been studied using thermoluminescent dosimeters in the Rando phantom. Measurement points were taken at three different depths in the midsagittal plane and at two locations out of that plane. The resultant radiation distribution for these points was measured at intervals of less than 1 mm. The measured dose distribution was compared to computer generated distributions. The field separation which resulted in the most ideal distribution for routine cases was determined. This agreed well with the field separation determined by the standard calculational approach, which may be used by modifying certain conditions. The application of the results of this data to the clinical situation is discussed.