Test purpose

The influence of the Integral Quality Monitor (IQM) transmission detector on the beam quality (beam hardening) was evaluated using data from nine
participating centres.

Test method

For 6 different nominal photon energies (4 standard, 2 FFF) and square field sizes from 1 cm × 1 cm to 20 cm × 20 cm, the effect of IQM on beam quality was assessed from the PDD20,10 values obtained from the percentage dose depth (PDD) curves, measured with and without IQM in the beam path.

Test results

The presence of IQM caused a small but measurable and statistically significant beam hardening effect. Beam hardening was most pronounced for the 6 MV FFF beam where it increased to 0.53%. Statistical significance of the beam hardening effect was demonstrated (p < 0.01) for all investigated beams except for 15 MV where no statistically
significant difference was found.


As beam quality changes were always lower than 0.53%, our conclusion is that this effect has no considerable clinical relevance.

This study demonstrates clinically negligible changes in beam quality for all investigated beams. Therefore, the time needed to implement the IQM system can be shortened since no additional commissioning is
needed regarding this beam property.