This paper focuses on some dosimetry aspects of proton therapy and pencil beam scanning based on the experience accumulated at Paul Scherrer Institute(PSI). The basic formalism for absolute dosimetry in proton therapy is outlined and the two main techniques and equipment to perform the primary beam monitor chamber calibration are presented. Depth-dose curve and lateral beam width measurements are exposed and discussed in detail, with particular attention to the size of the ionization chamber and the characteristic of scintillating-CCD dosimetry systems, respectively. It is also explained how the angular-spatial distribution of individual pencil beams can be determined in practice. The equipment and the techniques for performing regularmachine-specific quality checks are focused on (i)output constancy checks, (ii)pencil beam position and size checks and (iii)beam energy checks. Finally, patient-specific verification is addressed.
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