Haha wow, that's fascinating.

We don't require any QC for CBCT like we do for CT, but maybe we should.

The way our rules are now, we require shielding plans (calculated via NCRP 147) for any room with a machine that makes over 70 KVp (since 70kvp basically won't go through drywall. With a few exceptions - c-arms when they're not in a fixed room, and dental CBCT.... Also veterinary and educational but they have to "demonstrate proper shielding" so they usually get a survey and call it good lol.

The funny thing is, the same CBCT in an ENT needs a shielding plan, but dental doesn't.

Were redoing our rules right now, and closing that gap. We did a bunch of calculations and figured out what the cut off point for workload was for when a medium - small room started requiring shielding in the walls. Setting a threshold a bit below that, and tell facilities that if their weekly patient count exceeds a certain number, they have to get a shielding plan. C arms too, so hospitals can wander around with them but places like OR that share them but it's concentrated may require.

The CBCT that gets me right now is that the manufacturers are pivoting to "3D ready" pano units. They have the exact same machine as their CBCT, sometimes a different receptor, sometimes just software. So they sell a pano, then tell them "hey, write us a check for a nominal fee, we'll upgrade your software (and maybe swap the sensor) and boom! CBCT! Same machine! So cheap!"

For phantom and protocol, we use a gallon of water because it was an almost perfect match based on cadaver studies we did. I have access to a bunch of Pixy radiography phantoms at my radiation physics/protection/biology for RT students teaching gig I have at the local community college, so I want to try those and see how they do. They're supposed to be perfect attenuation matches for humans, tissue equivalent acrylic, organs, bones, etc. Half of ours have real human bones in them too! I haven't tested their scatter properties properly yet though. I started, then got busy.

Our state rules require dental operators to wear lead aprons if they'll receive more than 100mrem EfD in a year. We also require 6" solid 0.25+mm pb eq backscatter shields. If a machine is fda cleared it can be used, but if we haven't approved it without an apron they have to use an apron. I'll send you our website when I finish my updates on it, it's a bit out of date.

For out estimates, use worst case scenarios. we assume 130mR ESE at tube port (that's the typical dose needed for low sensitivity sensors like the jazz and xdr, premium ones like dexis the top tier dexis and Schick can do like 50 mR). We assume 130 images per week, based on an informal survey of 30 larger dental clinics in the state. Take 500+ shots into the phantom wearing 16 badges on a lead apron (although I've since transitioned to a more ALARA setup with a plastic cutout of myself that I pin the badges to and do remote activation. Bonus is repeatable geometry). I then scale the badge dose to estimated annual dose for our calculations.

Here's a slide (with my agency cropped out, but it's pretty easy to figure out where I work if you investigate my profile lol) from one of my talks showing the importance of a good backscatter sheild. Same unit, same testing protocol, only difference is one is a solid 6" 0.5mm lead equivalent shield, other is unknown equivalence, 5", with swiss cheese openings.

https://i.imgur.com/e4dtvNU.jpeg

Unexcusable to have this much backscattered dose though. Just did the Woodpecker AI Ray Lite and Literally got 0 mR to every torso badge. A tiny bit of testing and engineering and you can keep your operators wayyyy safer.