A phantom was set up on the tabletop to expose a lateral lumbar spine. We used 75 kVp, 200 mAs at a 40" SID. We did not actually expose an image plate for the lumbar spine, but we wanted to mainly focus on the scatter produced by that exposure.
So we measured 8 feet from the spine phantom and set up a 10x12 cassette vertically with a cassette holder. A hand phanotm was placed in front of the cassette and the exposure was made. The following image resulted on Kodak CR with an exposure index of 1190.
You can see that the scatter was enough to penetrate soft tissue and bone enough to see medulary canal.
We decided to re-create the experiment with the same spine phantom, but this time we placed a chest phantom upright next to a 14x17 cassette, approximately 6 feet away from the spine phantom at about the same height. We ended up with an exposure index of 980.
It was definitely enough to penetrate the lung fields, but may not have been enough to penetrate the shoulder or neck region. 6 feet is the minimum safe distance we should be on all portables... hopefully, this will make us think twice about wearing a lead apron when we shoot portables (especially on anatomy that requires a lot of technique).
As a side note, the chest image really allows us to visualize penumbra... or geometric unsharpness produced at the periphery of the anatomy. We know that the smaller the focal spot, the less the penumbra. We have essentially created a gigantic focal spot because the source of most of the radiation hitting the chest phantom was scattered from different points within the lumbar spine phantom on the table... approximately a 27cm focal spot size!
This is scary. I am an RT, ARRT who is 7 months pregnant and does alot of portables without wearing lead. However, where I work we only have one portable that is CR all the rest are DR. Have you done a study with DR?
ReplyDeleteI haven't done any studies with DR personally, but I wouldn't think the results would be very different if the generator power and technical factors are similar, since the scatter is coming mainly from the patient. That being said, you may want to consider informing your facility (if you already haven't) of your pregnancy so they can order you a fetal badge that should be worn underneath any lead apron at waist-level. If you are in a position to limit yourself from portables/fluoroscopy, that will help. I would also encourage you to wear a lead apron during all portables/fluoro, distance yourself as much as possible from the tube/patient, and limit the amount of time that you spend near any x-ray source. Make sure you are aware of your individual department and/or hospital policy regarding pregnant radiographers as well... you probably know all of these things, but I feel a sense of responsibility to mention them.
ReplyDeleteThank you for your response. As soon as I got the job back in March I informed my employer of my pregancy and filled out the papers my facility needed in order to get a fetal badge. But I didn't actually get the badge until Mid June. My employer just said it takes the company they order from awhile to send the badge. So I haven't even sent in my fetal badge yet to see if I am getting any radiation. I wore a lead apron the first couple days while I was doing portables but It started hurting my back and I was half way through the pregnancy I thought I would be in the clear to not wear one. I do not and have not done any fluro since I became pregnant and keep my distance at all times from the beam and do not hold any patients. I work in the ER of the hospital so have to do portables unfortuantly. Your blog is very informative, thanks for taking the time to write on it.
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