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In vivo dosimetry (IVD) is the last step of the quality assurance (QA) process in radiotherapy, providing an end-to end verification of the whole treatment. Modern IVD devices should be able to verify static and dynamic dose delivery and determine the most frequent and severe errors. An ideal IVD systems should act as a binary classifier by flagging incorrect fractions. Even if diodes are still the most popular devices for IVD, the use of electronic portal image device (EPID) is increasing, due to it's broad avalability and semplicity. Moreover, with EPID, the absorbed dose can be estimated not only in a point but also in a plane or even in 3D. The commissioning of an IVD device is aimed to verify the correct system implementation by testing the device functionality. It can be roughly divided in two parts. The first part consists in characterizing the basic device properties. The ability to correctly reproduce the delivered dose is therefore assessed. These tests includes:  dose linearity response, dose rate response, energy and angular dependence, field size response. The goal of the second commissioning part is to assess the specificity and sensitivity to determine typical errors. To this aim, realistic errors should be simulated and tested, against errors free treatments. ROC curve are constructed to quantify the device sensitivity and specificity. In this lecture, after a brief general introduction about the different strategies for IVD, the commissioning and quality assurance experiences, reported in literature, are reviewed. In the final part, a commissioning and QA protocol for EPID IVD, applicable to all kind of sofware, is presented.