Central-axis depth-dose data for diagnostic radiology

Depth-dose data have been measured for a range of irradiation conditions relevant to diagnostic radiology in order to provide a basis for the calculation of patient dosage arising from X-ray examinations. In general, data are required for larger field sizes, longer source-surface distances and greater tube filtrations than are commonly encountered in radiotherapy. Principles and techniques of measurement are discussed with particular attention to the specification of X-ray beam quality. It is recommended that both peak tube potential and first half-value thickness should be specified, especially for the determination of doses at depths of 5 cm or more. With the appropriate specification of quality, good agreement is found between these measurements and other compilations of depth-dose data for radiotherapy use. Zero-area depth-doses have also been measured and compared with calculated values derived from theoretical considerations of X-ray beam spectra.