Apparatus for commissioning or performing a quality assurance (QA) verification of a radiation therapy (RT) device (1) comprising (a) a motorised water phantom (3)； (b) a RT controller (10) configured for obtaining operation parameters of fields, and causing the RT device to emit a beam according to said operations parameters； (c) a QA controller (50) comprising a memory storing a measurements plan, said measurements plan comprising data defining a sequence of fields, and d) a reference radiation detector (4) adapted and positioned for intercepting said radiation beam and for measuring the dose rate of said radiation beam, said reference radiation detector being substantially transparent to said radiation beam. The QA controller comprises acquisition means for acquiring and storing the dose rate from said reference radiation detector, and computing means adapted for checking the synchronism between the dose rate from the field radiation detector and the dose rate from the reference radiation detector.
