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Frequency and Type of Errors Occurring When Using Look-Up Tables for Dose Calculations - a Retrospective Analysis

G Nelson*, V Sarkar , A Paxton , V Pigrish , D Spitznagel , B Salter , University Utah, Salt Lake City, UT


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: For a number of different treatment types (such as Total Body Irradiation, Total Skin Electron Therapy, etc.) most institutions utilize tables from databooks to perform the dose calculations. Each time someone manually looks up data from a large table and then copies the numbers for a manual calculation, there is potential for errors. While a second check effectively mitigates the potential error from such calculations, it doesn’t tell us how frequently such mistakes occur or the nature of the mistakes.

Methods: 5 years’ worth of TBI calculations were reviewed. Each calculation was re-performed and evaluated against the original calculation and original second check. Any discrepancies were noted and those discrepancies were checked to see if the number was the result of misreading from the look-up table, a typo, copying or skipping partially redundant steps, or rounding/avoiding interpolation. The number of calculations which contained these various types of discrepancies was tallied and percentages representing the frequency of said discrepancies were derived.

Results: None of the discrepancies resulted in an MU calculation difference of more than a few percent. Typos, looking up wrong values from tables, rounding/avoiding interpolation, and skipping steps occurred in 10.4% (± 3.1%), 6.3% (± 2.5%), 53.1% (± 5.1%), and 4.2% (± 2.0%) of MU calculations respectively.

Conclusion: While none of the discrepancies resulted in an MU calculation difference of more than a few percent, this review shows how frequently various discrepancies can occur. Typos and looking up the wrong value from a table are the steps most likely to potentially cause a miscalculation. Creating forms that calculate MU automatically from initial measurement data would reduce the number of times numbers are written/transcribed and eliminate the need to look up data in a table, thus reducing the chance for error.


Monitor Unit Calculations, Risk, Quality Control


IM/TH- Formal quality management tools: Failure modes and effects analysis

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