From: DACBR131 Date: Thu, 12 Mar 1998 09:35:18 EST Subject: Re: I need some help about x rays In a message dated 98-03-12 04:18:41 EST, chiropratica@bo.nettuno.it writes: << what is the quantity of radiation of a full spine (2 shots)>> It depends. Is the x-ray generator single phase (common) or high frequency (newer, since 1985, but less common). If all else is the same (film, screens, grids, processing, etc.) a high frequency system would reduce the dose 25 to 50%. Second, the film/screen combination can have similar effects. A 400 speed rare earth system (e.g. Kodak Lanex Regular screens and T Mat G film) would require 50% more dose that if you used a 600 speed system (e.g. Kodak Lanex Fast screens and T Mat G film). At Logan College of Chiropractic we use the 600 speed system for our routine sectional work but use a full speed film (T Mat H) to increase the speed of the system to 1200 for full spine/scoliosis films. Third, choice of grid. Because Logan College uses high frequency x-ray generators and 600/1200 speed film/screen combinations we have chosen 10:1 and 12:1 grid ratios to clean up the scatter radiation produced in the patient. However, as you add more lead in the higher ratio grids the radiation dose burden also increases. A 12:1 grids requires the use of approximately 15% more radiation to produce a film of equal density when compared to a 10:1 grid ratio. BTW I feel 8:1 grids are inadequate for routine chiropractic use. Not enough cleanup on large lateral lumbar patients. Fourth, selection of kVp. For the initial investigation of a potential scoliosis patient we choose 80 kVp. This provides a film of excellent contrast with our generator/grid/film/screen combination. However, since patients with scoliosis often have serial radiography to evaluate progression we do followups using 100 kVp (with an appropriate reduction in mAs and an acceptable loss of film contrast). This change reduces the dose to the patient by over 50%. Last, use of sectional filtration. Since the neck area is approximately 11 cm thick and the lumbar region might be 20 to 40 cm one MUST (IMHO) use sectional filtration over the cervical and upper dorsal region to avoid over exposure on the radiograph and of the radiosensitive structures (thyroid/bone marrow, etc.) Logan uses the Nolan filtration system. The New Zealand Department of Health (not quite sure of the proper name) tested these filters/gonad shields and demonstrated dose reduction to the patient up to 70% (on selected views) when compared to the nonfiltered approach while producing films of superior quality. Given the above (high frequency, 100 kVp, 12:1 grid, 1200 speed film/screen combination, sectional filters with the tube 72 inches away from the film) I was able to produce an excellect full spine film using about 125 mR (milliroentgens). I consider this about optimal and state of the art in 1998. <> We don't really know but everyone gets interested as doses approach 10 rads. <> To hard to tell but here are some items to consider. If you have a single phase systems and take nothing but full spine films on 200 speed film/screen combinations (yes, I see this from time to time in my film reading practice) I can suggest the tube will not last as long or produce as good films as if you had the set up above. With usage all anodes (where the x-rays are actually produced degrade. Pitting of the anode surface occurs (but minimized by high frequency generators). Slowly the focal spots grow in size. The vaporized tungsten progressively plates out on the inner surface of the tube creating a slowly increasing filtration of the beam. Because the silver bearings inside the tube cannot be lubricated they eventually wear out. <> Some make x-rays "forever". I am wary of the doctors who tell me the old x-ray machine is still perkin' along after 25 years. (This is from an actual conversation I had with an older practitioner) It is dangerous in the sense that with focal spot degredation image sharpness decreases. This causes loss of detail and could result in missed diagnoses. I think that is dangerous. <> TV's and neon tubes don't produce pure x radiation. Alpha and beta radiation are softer and more readily absorbed, adding to dose levels. It is not a fair comparison or analogy. <> For lateral or oblique or flexion/extension films, using the above mentioned equipment (600 speed for cervical) but non grid and FFD at 72" (under 12 cm you really don't need a grid and there is an "air gap" on these particular views) I have measured the dose around 25 mR. Sorry to be so long. Hope this helps. BTW please visit the new web site of the American Chiropractic College of Radiology at accr.org or dacbr.com Gary M. Guebert, D.C., DACBR -------------------------------- From: svendlu@post3.tele.dk Date: Fri, 13 Mar 1998 00:21:31 +0000 Subject: Re: I need some help about x rays > In a message dated 98-03-12 04:18:41 EST, chiropratica@bo.nettuno.it writes: > << what is the quantity of radiation of a full spine (2 shots)>> > > It depends. Is the x-ray generator single phase (common) or high frequency > (newer (since 1985) but less common). If all else is the same (film, > screens, grids, processing, etc.) a high frequency system would reduce the > dose 25 to 50%. Dear Dr Guebert! Excuse me for intruding with a question. In our clinic we have an old ~20 yr old double phase equipment - it has been modified from valve to solid state retifiers which gave a lot more stiff kV to the systen - Also we have changed the tube 2 times until we finally got an electrical brake installed. It works very reliable but is on its limit (from a speed point of view) because of electr.mech. relays. We cannot utilize the fastest film/folie systems - and have dreams about getting new equipment. Oh -My question?? I have always thought that the main advantage of high freq. equipment was its much lesser weight (less iron and oil in the tranformator) and I am not familiar with your promishing statement of radiation (dose) reduction. How do you explain it. Thank you in adv. Svend Lund, D.C. DK, Denmark svendlu@post3.tele.dk -------------------------- From: "The Doc" Subject: Re: I need some help about x rays Date: Fri, 13 Mar 1998 10:20:40 -1000 I'm sure some of our DACBR's on the list will respond with more exacting data. I will interject a few of my thoughts here. >One of my patient is asking me about the danger of x rays. As far as I >have studied Roentgenology 30 years ago and that we don't take x rays >ourselves in Europe. I guess my knowledge is not up to date. Many advancements in the last 30 years. Fast films, rare earth screens and improved chemistry make exposure minimal in most plain film pictures. New digital technology recently approved by the FDA allows direct import of an exposure (with normal levels of radiation) into the computer without use of films (musc as CT and MRI do now). From there, it can be "manipulated" to improve the image without loss of valuable data. >For example what is the quantity of radiation of a full spine (2 shots) >and what is the maximum one can take to be in real danger? >How long a tube last before it should be change? Depends upon the amount it is used. Most tubes used daily will be good 5-10 years. > and when it gets old is it more dangerous than a new one? Generally not. Usually emits a weaker beam and sometimes more diffuse due to wear of the annode degrading the "focus" of the beam. >Can we compare the quantity of radiation from a full spine shot and the >radiation of a television set or a neon tube. Does a full spine shot have >much more radiation than a simple cervical shot? Yes. MUCH more. However, proper columnation, patient protection, filtering etc. minimze the excess esposures and proper radiographic technique reduces the possibility of re-takes. Many DoC's prefer regional films (cerv/thor/lumb) since the exposure is (overall) less and the pictures can be columnated to provide better detail in each area. I'm sure you'll receive more input about the exact exposure levels from others. Hope this helps. ------------------------