Cone Beam vs. Conventional CT Scans: Radiation Levels?

Dr. W. asks:

In the Nov. 29 issue of the New England Journal of Medicine, David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc., of Columbia University, raised concerns over possible radiation effects of CT scans. Their study, which suggested that the current proportion of cancers attributable to CT-associated radiation could be as great as 1.5% to 2%, has since ignited significant debate in the medical community given the invaluable role that CT scans play in medical treatment. Many have claimed that Brenner and Hall’s research is flawed.

Nevertheless, I’m wondering how my fellow dental practitioners are reacting to this latest news on CT Scans? Have your patients questioned you about this? Is this really a concern for our cases? How should we address the issue? Finally, I’m wondering how this warning about CT scans extends to Cone Beam Volumetric CT scans that we use in dentistry? Am I correct in assuming that the radiation level is lower with Cone Beam CT (CBCT)?

32 thoughts on “Cone Beam vs. Conventional CT Scans: Radiation Levels?

  1. Hi

    I believe the amount of radiation from a cone beam ct is about that of two panorex images..

    Best
    Sheldon Lerner
    Blue Sky Bio Dental Implants

  2. With the iCAT, the reduction in exposure dose is via a pulsed exposure, and being able to select a “field of view”. If you are only interested in the maxilla, you can select a 6cm wide scan and include only the maxilla in the scan. there is no extraneous structures exposed. The total dose is less than conventional CT scans, the resolution is better, and it allows the option of taking further scans to assess the site (eg. one to triage the overall site, and one with a radiographic guide for planning guided surgery, or following sinus augmentation procedures) and end up with an overall reduction in patient exposure, and with much improved diagnostic information.

  3. Medical CT scans have a huge amount of radiation, while CBCT scans have only a fraction of the radiation. So, the article may have a point with medical CT, but not so much with CBCT.

    DrC

  4. I had a guest (a commercial pilot) ask these same questions this week, so I was glad for an excuse to look up some good, hard numbers. The 1.5 to 2% cancer RATE INCREASE (of a small number) from CT is based on whole-body medical CT and is only vaguely correlated to dental CBCT.

    However…..

    Every time we locate a prevously unseen abcess, persistant sinus obstruction, failing TMJ, deviated septum, obstructed airway or (rarely) cancer, we can dramatically improve a person’s life. Or save it. CBCT allows us to see things we simply cannot see in PAs or Panos, predictably place implants and grafts and to measure & monitor many structures in our “Speciality” area, the head & neck.

    From the conebeam.com site:

    We are exposed to radiation from natural sources every day. On average one is exposed to an effective dose of about 3 mSv per year from naturally occurring radioactive materials and cosmic radiation from outer space. The added dose from cosmic rays during a coast-to-coast round trip flight in a commercial airplane is about 0.03 mSv. Radon gas at our homes gives a background radiation level of about 2 mSv per year. To give a simple example, the radiation from one abdominal x-ray is the same as the natural radiation one is exposed to in 10 days.

    NOTE FROM ME: Milli SV, not the micro SVs of CBCT!

    NewTom gives info here:

    Sirona Galileos is only 29 MICRO Sv (not milli-)according to their page (other sources say 40 to 60). Our Imaging Sciences’ iCAT is about 100-130 MICRO SV for highest resolution scan (depending on field of view and scan time, our usual is half of that exposure.)

    Read this, CBCT starts page 41.
    Final conclusion (for me) is that CBCT is only a TINY fraction of background radiation and generally 10% of medical CT of the head. (whew! my previous brief research was confirmed!) They are typically only 1.8 – 2 times a pano. I also looked at some of the ICRP Publication 60 information, which generally corresponds. I feel better!

    Anyone with more precise numbers?
    Thanks for reading…

  5. OH, I almost forgot: Salivary glands absorb more than most other tissues. (Enamel rarely gets cancer… LOL) We need to consider all of this stuff when thinking of our patients’ health.

  6. An abdominal CT scan has about 20 mSv. An Icat CBCT scan has about 70 uSV. mSv = milli Seivert.
    uSv= micro Seivert. 150uSv is about an FMX dose. One mSv is equal to 1000 uSv. So one abdominal medical grade CT is about 20000 uSV or about 285 times more radiation than an Icat CBCT. Hope this helps.

  7. Nick, thanks for reminding everyone of the micro/milli Seivert calculation for those who forget(and using the “u” for micro, I wasn’t thinking.)Again, orders of magnitude difference between medical CT & CBCT.

  8. As far as my sources tell me:
    A conventional CT scan has 3 times the radiation of an iCAT scan. HOWEVER, the NewTom has 1/3 of the radiation dose of an iCAT. The NewTom also uses a very short cycle of radiation exposure. The image is taken in a 24 second “scan” during which the beam is on for less than 6 seconds. In 3 minutes, the image is processed and you are ready to go.

  9. These quantities are blatantly inaccurate. These so called “sources” are typically salespeople with limited knowledge and understanding of the subject, with an obvious motivation to portray their product in a favorable light, or at least cause some confusion, in order to compete with a superior system.

    The fact is that the effective dose delivered by a standard iCAT scan is at least 10 times less than a medical CT of the same region, but can be 20 to 30 times less in many instances, depending on the type of equipment and other factors. The effective dose from NewTom VG has not been published, but device physics dictates that it would be in the same range as the iCAT, since the receptor panel is of the same type. Newest published studies indicate that the iCAT’s effective dose for a full volume standard scan (31 uSv) is less than the numbers for NewTom 3G. Please contact me for a copy of this published study by Dr. John Ludlow, who is an Oral & Maxillofacial Radiologist at Univ. of North Carolina.

    As far as the scan and exposure time numbers, the total scan time in iCAT is 8.5 seconds (as opposed to 24 seconds in NewTom as quoted below), while the actual exposure time is 3.6 seconds (as compared to 6 seconds in NewTom). The image is processed in 30 seconds instead of 3 minutes in NewTom. This difference was vividly illustrated during the “3-D shoot off” at the ADA in San Francisco in September, when the iCAT scan was already up on the screen before the patient walked out of the imaging station, whereas scores of PowerPoint slides were presented and explained while waiting for the NewTom data to be reconstructed after a scan.

    Arun Singh

    Chief Technology Officer

    Imaging Sciences International.

  10. I agree with Arun. The dosages from the machines were compared and published in the Journal of Maxillofacial Radiology. There can be less exposure than that given by a FMX, while providing light years more information. I have unexpectedly found pathology many times that has changed the patient’s treatment and even helped them get needed medical and or dental care sooner than they would have otherwise because of earlier diagnosis. The more detailed information from the scan also helps determine the effect of bisphosphonates. The journal of Neuroradiolgy has published radiographic signs to watch for involving bisphosphonates. The cbcts allow earlier and more precise evaluation.

    Rand Redfern DDS, Max Imaging Colorado Springs, CO

  11. The infamous, and controversial, article on the New England Journal of Medicine has rekindled the polemics about whose machine is giving less radiation dose!
    I share the disdain of my esteemed colleague Arun Singh against “blatantly inaccurate” numbers spread by “salespeople with limited knowledge and understanding”. Especially when the numbers concern radiation measurements, radiation absorbed dose, and radiation (estimated) risk and detriment, topics (particularly the latter) upon which even experts and specialists disagree more often than not.
    However, I urge Arun not to fall into the trap of the “my CBCT gives less dose than your CBCT” contest (or the contest on other supposedly comparable performance) … in a forum where the initiative should primarily be left to the clinical users rather than to the representatives of the industry. Since statements on specific products have been made, however, I feel myself compelled (this time only) to counter-comment at least on the subject of radiation dose.

    The bottom line is that this (sterile) debate about radiation dose comparison between different CBCTs distracts the attention from the really important points, that is:
    (1) In all circumstances, radiation dose from any CBCT machine is at least one order of magnitude smaller than with conventional CT machines, yet with pretty comparable diagnostic yield (as pointed out already in many comments).
    (2) We talk here (and with panoramic machines, and with intraoral x-rays) of vanquishing small effective dose, so much so that its very measurement is controversial, even more so is the risk associated to it, which is always merely presumed and estimated (not directly measured) using a conventional and arbitrary model, that was originally devised for a different scope and context (protection of the general population from the consequences of the nuclear energy industry).

    Ironically, producing (and imparting) LESS radiation dose (or dose rate) is technically NEVER a problem, rather the opposite is true. The challenge is to achieve diagnostically-proper image quality with a given radiation dose – or properly balance the imparted radiation dose with the achievable diagnostic results.

    As said, the measurement of such (effective) doses and the interpretation of the detriment are pretty difficult. To date the works from John Ludlows et al. offer the only comprehensive data reported in scientific literature by independent researchers for dental CBCT machines, but also their interpretation is fraught with pitfalls. For instance, the numbers can change by a factor two depending upon what ICRP guideline is adopted. These difficulties contribute to the ambiguities of sometimes comparing apples with oranges, into which the “salespeople with limited knowledge and understanding” thrive.
    While the latest published (or publicly disclosed) studies that I know of (from Ludlow et al.) still show NewTom 3G at the bottom of the dose ranking (and below iCat), a direct comparison of the numbers (whatever they mean) for iCat or Galileos to those for NewTom 3G 12” is improper, because the Field of View and imaged volume with the latter is significantly larger than with the former two. A fair comparison might be with NewTom 3G in 9” FOV mode, that has a smaller imaged volume comparable to that of iCat and Galileos, but neither Ludlow nor anyone else (I believe) has measured and/or published it. It is evident that the dose in 9” mode should be less than in 12” mode.

    As to the dose imparted by NewTom VG, I can guarantee that it uses essentially the same technique factors (kV, mAs, distances) as in NewTom 3G, but the FOV is smaller, therefore the effective absorbed dose with NewTom VG must be even lower than with NewTom 3G 12”.

    Roberto Molteni
    Executive Vice President, Technology
    AFP Imaging / NewTomDental / QR

  12. While the dose from cone beam CT is on average perhaps an order of magnitude less than that applied in most medical helical/fan beam CT scans of equal volume, the concept of minimizing dose to that required for the task of diagnosis and image guidance should always be kept in mind. We should be developing suitable patient selection criteria, where possible collimating to the area necessary, and making the best use of the data set that is exposed by providing a thorough diagnostic evaluation (or having a suitable trained person read the volume where deemed necessary).

    Following several years of providing a cone-beam CT service, I can state that it is my opinion that 3D imaging is needed prior to implant placement in almost every case. I believe the procedure requirements are such that the risk from the dose is unlikely to exceed the risk of not having sufficient information to perform the task to the highest level of perfection possible. I have seen many implants placed without 3D guidance where it is obvious that the practitioner had no idea whatsoever where they had placed the implant.

  13. Again, CBCT is not standard of care and I welcome any lawsuits where a General dentist fails to diagnose something and then tries to claim “I was only looking at dental stuff”
    Maybe that will shut them up for awhile…CBCT is useful in some situations..just not a majority of them.

  14. You “welcome any lawsuits”? And what is your definition of the standard of care? The SOC is no longer what the majority of clinicians in a geographic area do but rather what a PRUDENT clinician woould do in a similar case. There is a CT on virtually every corner and an increasing number of CBCT’s available to every clinician who desires volumetric information. If you have morbidity in a case that could have been avoided with 3-dimensional information, you don’t have a prayer in the world to defend yourself in a suit. CT is the standard in medicine. Don’t you think that a jury will judge you based on available technology rather than the fact that you are “only a dentist”?

  15. Dr. Miller arent you the same guy that advocated removing the entire sinus membrane?

    Amazing how you never replied again in that thread.

    osseonewsdotcom/sinus-tear-how-long-to-wait-for-regraft/

    Please dont quote what you think the standard of care is.

  16. Actually, I was quoting Mike Pikos and his published work on removing the membrane if there is a serious tear and then tenting with a collagen membrane. If you feel you know more than Mike, why don’t you contact him directly.

    Second, as an expert reviewer for dental malpractice cases for over a decade, I am sharing with the readers of this website my experience with plaintiff attornies and their line of questioning in both depositions and in court. If you feel that you are a lawyer as well, then why don’t you change professions.

  17. Actually, Pikos doesnt advocate that any more, you must of caught that in one of his old lecture of his. In his more recent lectures he doesnt shys away from that standpoint. It actually well documented in the ENT lit that you dont remove all the sinus membrane as it doesnt come back ciliated and you basically subject a patient to a life of sinusitis. Maybe you need to contact Mike for an update before you remove all the sinus membrane.

    Not interested in being a Lawyer, I do well enough as a Dentist.

  18. In fact, Mike DOES advocate removing the entire membrane in the area where the graft is placed, but NOT superiorly. If there are traces of membrane between the graft and host bone, regeneration does not occur. And what do you think OMFS’s do when they perform a Le Fort procedure or orthagnathic surgery? They don’t seem to have a problem resecting the sinus membrane and their literature seems to say the opposite about regeneration.

    And, yes, I think it is better that you stick to your own profession. RJM

  19. Dr. Miller there is a big difference between resecting the sinus membrane versus removing it entirely. I heard Mike speak at conferences and he DOESNT ADVOCATE removing all the sinus membrane. If he is telling you that, then he is wrong. It is well documented in the ENT lit that removal of the membrane is a NO NO. When you resect the membrane as in a La Fort procedure you leave the sinus membrane behind and it heals via ciliated epithelium. When you REMOVE the sinus membrane as you are advocating you are subjecting a patient to a lifelong battle with Sinusitis because it doesnt heal via ciliated epith. By the way, do you understand what the cilia does in the Sinus?

    If you actually did research at that Atlantic coast Research institute and not just get paid for CE you would know that you dont remove the membrane.

    Here is just a small sample of articles and there are many others:

    Melgarejo-Moreno PJ, Ribera-Cortada I, Sarroca-Capell E. Rhinology. Radical or partial maxillary sinus surgery: a dilemma today? An experimental study 1996 Jun;34(2):110-3.

    Benninger MS, Schmidt JL, Crissman JD, Gottlieb C. Mucociliary function following sinus mucosal regeneration. Otolaryngol Head Neck Surg. 1991 Nov;105(5):641-8.

    Forsgren K, Stierna P, Kumlien J, Carlsöö B. Regeneration of maxillary sinus mucosa following surgical removal. Experimental study in rabbits. Ann Otol Rhinol Laryngol. 1993 Jun;102(6):459-66.

    Benninger MS, Schmidt JL, Crissman JD, Gottlieb C .Mucociliary function following sinus mucosal regeneration. Otolaryngol Head Neck Surg. 1991 Nov;105(5):641-8.

    I certainly hope you are never an expert in a OMFS case, the lawyers and the surgeons would have a field day with you.

    TJH

  20. READ MY POST. I state that you do NOT remove the membrane superiorly if there is a major tear. But you CANNOT leave remnants of the membrane between the graft and host bone or regeneration does not occur. That area must be debrided completely.

    I have never been paid anything for my work at the Atlantic COast Dental Research Clinic. We teach there solely for the love of the discipline and contribute to the body of knowledge.

    And, finally, my name is not McCoy, so whatever your problem is, leave it at the door and refrain from ad hominum attacks. RJM

  21. Dr Miller Im not attacking you. But there are readers of this site with various experience in implant therapy. When you make blanket statements like this it teaches novices to be cowboys:

    Dr Miller quote “Especially when quoting Mike Pikos. Mike routinely uses a membrane to cover perforations. In fact, in his article on management of sinus perforations in the journal Implant Dentistry, if there is a large peforation (in the absence of sinusitis), he will remove the memerane entirely to mid-sinus and recreate the floor with a membrane, not abandon the procedure.”

    You have more experience then most General dentists in the field of implant dentistry but we all have alot to learn including you.

    We need to first do no harm. I would never advise other dentists that if you have a large perforation just remove the sinus membrane in its entirety. I think I have shown you the harm this could cause. The sinus membrane is there for a reason, dont advise new implant surgeons that just remove it if you get a large perf. That my friend is a recipe for disaster.

    Although, I like your McCoy comment, we dont have to meet at the OK carral yet.

  22. In response to Mike Stanley numbers that have appear to be conjured out of thin air.
    A standard abdo AP x-ray is about 4mGy (4mSv) not 3/(365.25/10)= 0.082 mSv

    To give a simple example, the radiation from one abdominal x-ray is the same as the natural radiation (3mSv) one is exposed to in 10 days.

    Where did you get this figure from, the dose in one abdo ap examination is greater that the yearly background and certainly not a tiny percentage of it.
    The NRPB (national radiological protection board) gives a limit to 7 mSv per abdo scan.

    Could somebody explain to me why cone beam CT dental images are necessary? The standard digital/film based OPG procedures produce nearly the same standard image at a fraction of the dose. Therefore how can the use of CBCT be justified to a patient. I’m sure most people educated about the health risks with CBCT would decide against it and opt for the lower alternative.

  23. Dear All,

    Perhaps the following website may be of use – Please put a www. in front to the following;

    radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray&bhcp=1

    This page gives both the approximate doses for various radiological interventions as well as how that dose compares with natural background radiation doses.

    I hope that this is useful (I have no affiliation with the site) and that Osseonews doesn’t “Edit” the link out of this post.

    Kind Regards,

    Bill Schaeffer

  24. How do you not abandon the bone augmentation if you get large sinus perfs from lateral entry. I had to abandon the procedures and placed pericardium membraned and the flap over it. no bone. I just cant imagine placing a free floating bone particles with no stability

  25. For Glenn Booker: Follow the links given in my post. Then follow the other links in this thread. I don’t recall that ANY of the data I located was specific to abdominal scans.
    As for why volumetric imaging vs 2-D films? Implants are placed in 3-D space. Volumetric scans help us to find appropriate locations and indicate (to a degree) bone density, thus improving predicability and long-term outcome. Place a maxillary implant based only on a pan and a flap, you’ll be in a sinus half the time. Probably more in the posterior.
    All is just background information, if you want hard numbers, you’ll have to do more reading than here in this blog. You seem like a numbers guy. Read the initial question again, then find your own numbers. Have fun!

  26. It is very interesting and informative to read this post. I would like to add that when a source offers radiation level of the ICAT, it is often unclear which generation of ICAT is being talked about. Also, Imaging Sciences publish an internal study of radiation levels from the center of the field to something like 9 feet from it in the ICAT manual. I have the lastest version of ICAT in the office. This may be on source of radiation level information for the ICAT CBCT.

    Tony Woo, DDS
    Oral Surgeon
    Medford, Massachusetts

  27. You’ll find a lot more information about studies comparing the radiation dose (effective dose) of various CBCT scans at the Worldwide Orthodontic Forum: http://dontics.org/forum. (You’ll need to register there, but it’s free and although intended for orthodontists, no one is rejected who has an interest in the subjects. In the 3D Imaging board, there are many topics relating to who needs a CBCT scan, how safe is it, when does the benefit justify the increased risk of radiation induced cancer versus other diagnostic techniques, etc.

  28. I find it amazing how techniques make a full circle over a period of time. Mike Pikos was lecturing at the ICOI meeting in Vancouver last month on diagnosing and treating mucocoeles in the maxillary sinus. He, once again, espouses FULL removal of the sinus lining when removing a mucocoele. If you do not remove the lining, there is a high recurrence rate of mucoecele regeneration.
    RJM

  29. What all of yall seem to be over looking is the fact the lower the radioactive dose the higher the skin attenuation. Which inturn means greater reaction or possibility of cancner. The Higher the dose the more penetrating the radiation is and the LESS likely hood of attenuation. Attenuation is your enemy. Just because the dose is lower does not mean it is better. There is a balance point when it comes to Pt. Dose vs attenuation. There are 3 basic rules to Radiation. Time, Distance and Sheilding. You might want to think about all this on your next low dose Cone Beam CT.

  30. Dustin, please explain more about attenuation in regards to radiation levels and skin. Do you mean the skin gets thinner?
    Thank you

  31. Dustin, I think you may be confusuing Dosage with Kilovoltage. Lower Kilovotage xrays are more easily attenuated (read absorbed)in soft tisuue, and therefore lower dosages are required to penetrate to the film. Older 55kV AC or pulsed Intra Oral X-rays had relatively large skin dosages and absorbation rates to expose “D” speed films as the beams from the contain a high percentage of “soft” radiation.This forum is talking about dosages that are comparively smaller, escpecially when the field of view is considered, than your old 55kV I/O x-ray with dip tanks was.

  32. Need help in deciding to go in for a 3D OPG machine or a CBCT with a smaller FOV,I practise head and neck radiology in India. Intention is purely for implant purposes, small lesions of the U/L jaws,number and direction of roots and root canals,expansile lesions of jaws and impactions.The dealers here keep telling me that the 3D OPG is as good as the CBCT and much cheaper. since there is no installation as yet, i need help from all who have used both these machines. regards Dr tatu

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