"Anode heel effect" on patient dose in lumbar spine radiography

Appropriate use of the "anode heel effect" of the output beam from an X-ray tube can reduce the effective dose to patients in some common radiological examinations. We investigated the variation in radiation intensity across the X-ray beam caused by the anode heel effect, and quantified the differen ce in absorbed dose to critical organs resulting from lumbar spine X-ray pr ojections carried out with the two possible orientations of the patient alo ng the tube axis (cathode to anode). A Rando phantom and some high sensitiv ity thermoluminescent dosemeters (TLDs) (LiF:Mg,Cu,P) were used. With the t ube axis horizontal, radiation intensity profiles, parallel and perpendicul ar to the axis, were measured. Lumbar spine radiographs were recorded using the Rando phantom in the standard anteroposterior (AP) and lateral project ions. TLD pellets were used to measure the absorbed radiation dose at vario us sites corresponding to critical organ tissues (ovaries, testes, breasts, thyroid and lens). Each set of projections was recorded in two phantom ori entations, first with the phantom head placed towards the cathode end of th e X-ray tube, and then in the reverse direction. From the radiation intensi ty profile of the incident X-ray beam, the "cathode end" to "anode end" air dose ratio was found to be 1.8. In lumbar spine radiography, with the phan tom head placed towards the anode end of the X-ray tube, the ovaries and te stes received an average dose 17% and 12% higher, respectively, in the late ral projection, and 16% and 27% higher, respectively, in the AP projection, than those obtained in the reverse "patient" orientation. These results in dicate that patients (particularly females) should always be positioned wit h the head placed towards the cathode end of the X-ray tube for lumbar spin e radiography to achieve significant dose reductions.