From: Ian and Louise Smalley <[EMAIL PROTECTED]> Here is my take on this Ric,
Assuming the LBD accurately portrays the area of the incident beam, the best control the dose from primary beam is through careful collimation. Now for scatter: Assuming careful alignment of the beam and the patient to eliminate the presence of unwanted artefact (drip stands, structural columns etc), the first opportunity for the generation of scatter is obviously the patient and scatter continues to be generated at just about every interface through to and including the wall. Major scatter is generated by the bed frame of which a fair chunk deflects back toward the patient. Placing Pb protection on the waist (on the tube side) of the patient is an effective way of preventing scatter from exiting the patient, similarly placing Pb protection on the cassette side will prevent scatter exiting the patient, but this approach will prevent much of the bed-generated scatter actually entering the patient. With respect to scatter generated within the patient, there is not a lot we can do to protect the internal organs (including ovaries), but as the testes are external (mine are kept on the fridge) there are options for the very keen radiographer. An old boss of mine (sorry about the "old" Glen Burt) was an advocate of attempting every mobile chest x-ray as a PA examination with the patient sitting with legs off the side of the bed. This gave good geometry and eliminates sources of backscatter. It also sent the residual beam off to the patient in the next bed, but distances usually made this acceptable. Ultimately, dose reduction on mobiles is not too different from fixed equipment. Maintain your equipment, collimate carefully and get positioning and exposure right the first time. Too easy! The above views on scatter are to be best of my knowledge totally untested by scientific study. Which brings me to my "Why do they do that?" question. Why do radiographers place Pb protection on the lap of a patient having a knee examination when the sources of scatter (the knee, the cassette and table/bucky structures) are ALL underneath the Pb protection? Surely rather than teach this nonsense to students we should calculate dose to the gonads (is it actually a significant dose?), or encourage protection to be placed under the patient and/or curved between the thighs as indicated by each view. Ian Smalley ________________________________ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Eric Yeomans Sent: Thursday, 11 September 2003 4:59 PM To: undisclosed-recipients: Subject: [AIRNEWS] Pb protection for mobile chests From: "Eric Yeomans" <[EMAIL PROTECTED]> I have always thought using a Pb shield while doing young moblie chest x-rays, the right thing to do. Recently a comrade stated that there was actually no radiation protection to the patient by such action and that we were partaking in a PR exercise by supplying Pb protection for mobile chest x-rays. Is this correct? Ric Yeomans Medical Imaging Orange Base Hospital Ph 6393 3569 Fax 6393 3574 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+= This message is being broadcast by AIRNEWS, the Australian Institute of Radiography list Server Send messages to [EMAIL PROTECTED] For assistance send mail to [EMAIL PROTECTED] Commands should be sent to [EMAIL PROTECTED] Opinions expressed on this list are not necessarily those of the moderator, his assistants or those of the A.I.R.
