Test purpose
The short-term signal reproducibility test verifies the IQM detector’s capability to measure the same signal when the same beam is repeated multiple times.
Test method
The signal reproducibility test uses the reference field size of 10 cm x 10 cm (defined by MLC and Jaws) for a 6MV photon beam delivering 100 MUs. The test is passed if the variation of the measured signal is 0.50% or less.
Test results
The coefficient of variation (%SD) varies for all sites from 0.03% to 0.13% and is diagrammed in the figure below.
For further analysis the individual deviation from the average for every single test run was investigated. The same pass criteria as for the coefficient of variation (namely 0.50% or less) was applied for the deviation from mean. The results are shown in the figure below. The deviation from mean varies from 0.01% to 0.23% which indicates a small variation for the different test runs.
This is confirmed when inspecting the signal values for all 10 runs at all 18 linear accelerators /sites (in table 2 of the white paper). Within each site, test run results show minimal variation. This small variation is due to tolerances from the IQM (<+/- 0.50%) and slight Linac output variations.
Conclusion
Every IQM installed at each RT department passed the criteria for reproducibility, with a coefficient of variation under 0.50%. The results indicate a high reproducibility with low variation within all 10 test runs for each of the IQM systems installed.
