This book aims at improving clinical photon beam dosimetry based on understanding commissioning the new linear accelerator and dosimetry principle underlying, understanding physical parameters that affect dosimetric properties of clinical photon beams, understand the need for accurate characterization of clinical photon beams of clinical photon beams in a treatment planning system, and acquire necessary and sufficient skills in setting the new dosimetry equipment. In addition determine the absolute dose to the water using IAEA TRS-398 protocol.