Modern radiation therapy technologies such as IMRT, VMAT and TomoTherapy create complex composite dose distributions that are specific for each patient. To verify that the planned dose is delivered correctly, the QA system must measure the dose with much higher accuracy than the calculation accuracy in the planning system. This can only be achieved by actually measuring the dose - both the direct and the indirect contribution from all beams in each fixed position - with high spatial resolution and high resolution in dose.