Correspondence

Abstract

Many deep therapy machines now available in the 250 kV range have “coarse” and “fine” autotransformer tapping controls for kV adjustment. Although regulation to 1 or 2 kV is thus possible, line-voltage changes due either to a local load variation on the same line or to regional “load-shedding” can, in many cases, be rectified only by first switching off the HT supply to the X-ray tube. This time-consuming process is an annoyance to the operator, while failure to make the necessary adjustment must result in a loss of accuracy in dosage.