Chapter 6 External Photon Beams: Physical Aspects - IRSN

376.8 CENTRAL AXIS DEPTH DOSES IN WATER: SAD SETUPSAD setups are used in treatment of deep seated tumourswith multiple beams or with rotational beams.In comparison with constant SSD setup that relies on PDDdistributions, the SAD setup is more practical and relies onother dose functions such as:• Tissue-air ratio (TAR)• Tissue-phantom ration (TPR)• Tissue-maximum ratio (TMR)IAEA Radiation Oncology Physics: A Handbook for Teachers and Students - 6.8 Slide 1 (73/170)6.8 CENTRAL AXIS DEPTH DOSES IN WATER: SAD SETUP6.8.1 Tissue-air ratioTissue-air ratio (TAR) wasintroduced by Johns tosimplify dose calculations inrotational radiotherapy butis now also used fortreatment with multiplestationary beams.The SSD varies from onebeam to another; however,the source-axis distanceSAD remains constant.IAEA Radiation Oncology Physics: A Handbook for Teachers and Students - 6.8.1 Slide 1 (74/170)