![]() Also, the variation of the 15o, 30o and 45o wedge TF with field size was less significant (less than 2%) and a weaker dependence was observed with field size as compared to the treatment depth. Maximum percentage variation for the 15o wedge for the SAD setup was 1.1% and 1.59% for the SSD setup and that for the tray was 0.60% for the SAD setup and 0.12% for the SSD setup. ![]() Also, the results obtained showed that both the wedge TF and the tray TF has a strong linear dependence on treatment depth however, the variation of the 15o wedge TF and the tray TF with depth is less significant (less than 2%). Wedge and tray TF measurements were performed in a full scatter, large water phantom using a 0.04cc ionization chamber and an average photon energy of 1.25MV from a cobalt-60 unit at an SAD/SSD of 100cm at various depths and field sizes with gantry and collimator angles fixed at 0o. The purpose of this research work is to evaluate the variation (or dependence) of the transmission factors (TFs) of block tray and physical wedges (of different angles) as a function of treatment depth and field size using both iso-centric setups, SAD and SSD and thus compare the results from the two setup techniques. ABSTRACT The use of beam modifiers in today’s radiotherapy is very important as it attenuates the beam and reduces the dose to the patient therefore the need to know the amount of attenuation (in terms of a transmission factor) they provide during treatment.
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