title: Effects of irradiation geometry on treatment plan optimization with linac-based radiosurgery.
abstract: A comparison was made of different treatment plans to determine the effect on the three-dimensional dose distributions of varying the allowed parameters in linac-based stereotactic radiosurgery with circular collimators; these parameters are arc position, length, and weighting, and collimator diameter. For the class of eccentrically shaped target volumes that are not so irregular as to require several separate isocenters, it was found that superior dose distributions could be achieved by varying arc length, arc position, arc weighting, and collimator diameter. An analysis of the results achieved with an automated planning program indicates that, in general, the variables of arc position and arc length are of greater importance than collimator size or beam weighting. However, there are cases where varying these latter two parameters does result in markedly better dose distributions. A deeper investigation into the effects of multiple collimators on the dose distribution in the area of steepest gradient demonstrated that multiple collimator sizes do not significantly degrade the dose falloff, which is in fact mostly determined by the effects of intersecting arcs.
authors.affiliation: Department of Radiation Oncology, University of Washington Medical Center, Seattle 98195-6043, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Phillips
authors.forename: K J
authors.initials: KJ
authors.lastname: Stelzer
authors.forename: M R
authors.initials: MR
authors.lastname: Mayberg
authors.forename: H R
authors.initials: HR
authors.lastname: Winn
mesh_terms: D001932:Brain Neoplasms / Q000556:secondary / Q000601:surgery*; D006801:Humans; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted; D012189:Retrospective Studies