Test purpose

Evaluate the correlation between changes in IQM signal, Gamma-Index and Dose Volume Histogram.

Test method

The sensitivity of detecting small delivery errors was checked by inducing seven types of errors in the IMRT clinical plans for head & neck, prostate and the IQM test plan by modifying the number of delivered MU (between 1 and 3 per beam) and by introducing deviations in linac leaf positions mimicking an MLC bank error as closing and opening one or both banks. The influence of those errors on the IQM signal, the change in Gamma Index as well as the influence on the dose volume histogram (PTV V95%) was analyzed.

Test results

IQM signal variation is plotted vs 2D Gamma per beam (1%/1mm, th10, local approach) and the PTV V95% for the H&N example. The correlation function R shows a good correlation especially with DVH parameters.


A good correlation between IQM signal variations and 3D Gamma, 2D Gamma and DVH parameters has been observed.