Wedge factor changes with depth and field size on a linear accelerator with a motorized wedge.
The wedge factor was experimentally determined as a function of field size and phantom depth for 6-MV X-rays; measurements were performed on a linear accelerator with a motorized wedge filter (universal wedge, nominal wedge angle = 60 degrees). As a result of our experimental work, we can state that: 1) The wedge factor increases linearly with phantom depth (0.275%/cm), almost independent of field size; this change was experimentally related to the beam "hardening" caused by the high Z value of wedge material, as shown by the increase in wedged-field PDD with respect to the corresponding open-field PDD. Neglecting this variation can induce systematic errors in delivered dose, especially when deep-seated tumors are treated with wedge fields. 2) The wedge factor changes, for rectangular fields, according to the "equivalent square law", and not to the dimension in the wedged direction.
Raffaele
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L
IST-Istituto Scientifico per lo studio dei Tumori, Genova.
Settineri
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N
Pergolizzi
S
S
D'Angelo
A
A
D005374:Filtration / Q000295:instrumentation; D006801:Humans; D010315:Particle Accelerators / Q000295:instrumentation* / Q000706:statistics & numerical data; D019047:Phantoms, Imaging / Q000706:statistics & numerical data; D011878:Radiotherapy / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data