Measurement of Bone Marrow and Gonadal Dose from X-ray Examinations of the Pelvis, Hip and Spine as a Function of Field Size, Tube Kilovoltage and added Filtration

Abstract

Detailed measurements have been made of the dose absorbed by the bone marrow and by the reproductive organs of a realistic human phantom exposed to antero-posterior and lateral radiographic examinations of the pelvis, lumbar spine, thoracic spine and cervical spine, and to the antero-posterior examination of the hip. The measurements were made over a range of parameters including kilovoltage, filtration, and useful beam size. The kilovoltage, range extended, for most of the examinations, from 60 to 110 kVp. The effect of added filtrations of 1 and 2 mm Al was determined for most cases. In general, measurements were made for two X-ray field arrangements. Arrangement A, provided by a well-shielded collimator, yielded a field just large enough to cover the film of interest. Arrangement B was provided by a conventional radiographic cone yielding a field usually considerably larger than the film. The method of measurement involved the use of small ionization chambers which exhibited a high degree of energy, directional and dose-rate independence in the diagnostic X-ray energy region. The results are expressed in units of dose per mAs of X-ray machine exposure. Expressed in this way, these measured ratios are independent of the kind of film used, the type of cassette, screen or Bucky used, and of the subjectivity involved in determining the mAs exposure required to obtain a satisfactory radiograph. The values of these ratios can be applied to any particular choice of the above variables. The measured values of marrow exposure dose at representative sites were weighted in accordance with the fractional distribution of active marrow to yield the average active marrow absorbed dose per unit of mAs exposure. Complete tables of the measurements are given. By interpolation estimates of bone marrow and gonadal exposure can be made for any procedure using parameters within the range studied.