Influence of the Integral Quality Monitor transmission detector on high energy photon beams: A multi-centre study

The influence of the Integral Quality Monitor (IQM) transmission detector on photon beam properties was evaluated in a preclinical phase, using data from nine participating centres: (i) the change of beam quality (beam hardening), (ii) the influence on surface dose, and (iii) the attenuation of the IQM detector. For 6 different nominal photon energies (4 standard, 2 FFF) and square field sizes from 1×1cm2 to 20×20cm2, 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. The change in surface dose with/without IQM was assessed for all available energies and field sizes from 4×4cm2 to 20×20cm2. The transmission factor was calculated by means of measured absorbed dose at 10cm depth for all available energies and field sizes. (i) A small (0.11–0.53%) yet statistically significant beam hardening effect was observed, depending on photon beam energy. (ii) The increase in surface dose correlated with field size (p