A Rapid and Convenient Method of Checking the Kilovoltage in X-ray Therapy

Experience with a number of deep X-ray therapy units has shown that variations in X-ray output occur, which are often due to changes in the kilo-voltage operating across the X-ray tube. By utilising the well-known property that, over a range of quality, suitably chosen filters of different atomic number behave differently as regards their X-ray absorption, a simple method for detecting such changes in potential has been developed, which can be used conveniently in an X-ray therapy department. The method consists simply in measuring the intensity of the X-ray beam when (a) heavily and (b) lightly filtered. The ratio of the two intensities is found to serve as a sensitive indication of the applied kilovoltage, and hence of the quality of the beam. The filters usually met with in an X-ray therapy department serve well for the purpose of the test.