- Design
- Quality improvement initiative, pre-post comparison
- Population
- Adults undergoing renal stone surveillance at one US institution
- Primary outcome
- Monthly ultrasound use for stone surveillance
- Effect
- Ultrasound 35 to 10 per month (−71.4%); dose 5 to 1.7 mSv
A US quality improvement project used a Six Sigma framework to move renal stone surveillance from ultrasound and KUB radiography to a tin-filter ultra-low-dose CT protocol. Drivers of ultrasound use were radiation concern and lack of awareness.
The protocol cut mean dose by 66%, from 5 to 1.7 mSv, against standard low-dose non-contrast CT. In the sustained phase, ultrasound fell from a median 35 to 10 examinations a month (71.4%), KUB from 15 to 4, and ultra-low-dose CT rose from 0 to 43.5. The Medicare fee for CT was $47 higher than ultrasound plus KUB, before counting the second visit the pair requires.
CT is more accurate than ultrasound and KUB for stone size and location. At under 2 mSv, the radiation argument against it largely falls away. Whether a local scanner can deliver a comparable protocol is the practical question to settle with physics.
- Build an ultra-low-dose stone protocol if your scanner supports tin filtration or equivalent.
- Agree with urology that it is the default for adult stone surveillance.
- Keep ultrasound for pregnancy, children and hydronephrosis checks.
- Track dose and utilisation after introduction.
Why it matters
It removes the main reason stone patients are followed with less accurate tests.
Don't overread it
This is a single-institution quality project measuring utilisation, not patient outcomes.
The statistics, in plain English
A 71% fall in ultrasound is the median monthly count before and after, not a trial result. The dose saving of 66% is relative to standard low-dose CT, not to ultrasound, which has none.
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