Megavoltage photon radiation therapies are widely used in modern cancer treatment. The improvement of the treatment has lead to the need of Quality Assurance (QA) devices to detect malfunctioning or human mistakes during the planning phase and treatment verification. Active electronic devices for 2D or 3D QA in external beam radiotherapy are typically based on analogue/digital mixed signal Data Acquisition Systems (DAS) which are required to have high spatial resolution, large dynamic range, high sensitivity, large numbers of channels and fast real-time capabilities. The Centre of Medical Radiation Physics (CMRP) has developed several multichannel DAS architectures based on different analogue front-ends to suit a wide range of radiotherapy applications. For the purpose of this study, two DAS, with different front-ends, have been equipped with 128 channels and tested in a clinical environment. Data show a good agreement within 1% between the two systems and the ionising chamber currently used for daily QA.