SU‐E‐T‐191: Evaluation of a Commercial QA Device for Daily Output Check for a Large Multi‐LINAC Institution

Purpose: To quantify the difference between the daily output readings of a Daily QA device and monthly output readings and to determine at what frequency these devices need recalibration. Methods: Daily QA 3 (Sun Nuclear, Melbourne, FL) devices were used on 17 Clinac 6EX and Varian 2100C/D/EX LINACs to measure daily output over a period of 6 months for 2 photon energies and 5 electron energies for each machine. These devices measure output using an open ionization chamber that is corrected for temperature and pressure by internal sensors. The daily output was averaged each month across all days and compared to the monthly output readings taken using a temperature/pressure corrected farmer chamber and PMMA blocks. Results: The average difference across all energies and all machines across all months was 0.3% ±0.7%, indicating a good level of stability for slope was found to be consistent with a −.07% per month change in Daily QA 3 readings over the 6 month time period investigated. This change was not found to be a function of energy or radiation type (X‐rays or electrons). However, device‐dependent variation was noted in drift with values from ‐ 0.3%/month to + 0.1%/month. Conclusions: The data collected in this study indicates that although the Daily QA 3 device is a robust and simple to use machine capable of several tests, it would be prudent to verify these devices against a transfer quality dosimetry system monthly and recalibrate as necessary, with an expected frequency between 3 months and 1 year.