title: Head-scatter factors in blocked photon fields.
abstract: The behavior of the head-scatter factor in shielded 6 and 25 MV X-ray beams from a Philips SL25 linear accelerator was investigated by measuring incident fluences by direct (in-air) and indirect (in-phantom) methods. It was found that perturbations in head-scatter produced by shielding blocks arranged to define a slit-shaped field are considerably less than 1% in unwedged beams, even when 80% of a 20 x 20 cm2 field is shielded. The results are independent of beam energy and orientation of the slit with respect to the collimator jaws. When a 60 degrees wedge is inserted, the head-scatter factor decreases by up to a few percent, depending on slit direction but not on energy. The contributions to head-scatter from the block tray and the shielding blocks are negligible.
authors.affiliation: Roger Williams Cancer Centre, Brown University, Providence, RI 02908.
authors.forename: M
authors.initials: M
authors.lastname: Tatcher
authors.forename: B E
authors.initials: BE
authors.lastname: Bjärngard
mesh_terms: D000180:Acrylic Resins; D000388:Air; D006801:Humans; D007854:Lead; D008433:Mathematics; D008961:Models, Structural; D010315:Particle Accelerators; D017785:Photons; D011835:Radiation Protection / Q000295:instrumentation; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation; D012542:Scattering, Radiation
chemical_list: D000180:Acrylic Resins; D007854:Lead