Ultra-low-dose CT at 1.7 mSv replaced most ultrasound and radiographs for renal stone surveillance

Design

Single-institution quality improvement project (Six Sigma DMAIC), before-after

Population

Patients undergoing renal stone surveillance imaging

Primary outcome

Monthly ultrasound use; secondary radiograph use, dose and cost

Effect

Dose 5 to 1.7 mSv; ultrasound 35 to 10 per month (-71.4%); radiographs 15 to 4

A US multidisciplinary quality improvement project, using the Six Sigma framework, introduced a tin-filter ultra-low-dose CT protocol for renal stone surveillance and recommended CT for follow-up imaging.

Mean dose fell 66%, from 5 mSv with standard low-dose CT to 1.7 mSv. In the sustained phase, median monthly ultrasound examinations fell from 35 to 10 (71.4%) and radiographs from 15 to 4, while ultra-low-dose CT rose from 0 to 43.5 a month. The Medicare fee was $180.82 for the CT against $133.59 for ultrasound plus radiograph.

Ultrasound and radiographs are used for stone follow-up mostly because of radiation worries, yet they miss and mis-size stones. At a dose close to that of a few radiographs, CT answers the question better in one visit.

The cost comparison is specific to US Medicare fees and will differ in Indian practice, where ultrasound is much cheaper and ultra-low-dose tin-filter protocols depend on scanner capability.

• Check whether your scanner supports a tin-filter or equivalent ultra-low-dose protocol.
• Agree with urology which surveillance questions CT should answer: size, number and location.
• Replace ultrasound-plus-radiograph pairs with a single ultra-low-dose CT where available.
• Keep ultrasound for pregnancy, children and hydronephrosis checks where radiation should be avoided.

Why it matters

Radiation worry has kept stone follow-up on less accurate tests, and a sub-2 mSv CT removes most of that objection.

Don't overread it

This was a single-institution quality improvement project measuring imaging use and dose, not stone outcomes or diagnostic accuracy.

The statistics, in plain English

Medians with interquartile ranges describe typical monthly volumes; the p-values show the change is unlikely to be random month-to-month variation. The study did not measure whether patients' stone care improved.

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