title: Stereotactic radiotherapy of irregular targets: a comparison between static conformal beams and non-coplanar arcs.
abstract: Stereotactic radiotherapy using a linear accelerator is usually equated with the technique of delivery using multiple non-coplanar arcs, which achieves a spherical dose distribution. As the majority of intracranial lesions are not spherical, a range of schematized tumour shapes were planned to assess the role of static conformal beams in the treatment of irregular lesions. A sphere and 2 ellipsoids, ranging from 20 to 50 mm maximum diameter located intracranially were planned using 3, 4, and 6 non-coplanar static beams with conformal blocks and were compared with four 120 degree non-coplanar arcs. Comparison of the plans was made by the relative sparing of normal tissue outside the target volume using three-dimensional dose-volume distributions. Non-coplanar arcs spared more normal tissue at low isodoses and achieved the best high dose sparing for spherical targets. For the majority of irregular targets, 3 and 4 static beams spared more tissue at doses > or = 50% and > or = 80% than the arc technique. For all irregular volumes, maximum sparing of normal tissue to isodoses > or = 50% and > or = 80% of the treatment isodose was obtained with 6 static conformal beams. We conclude that irregularly shaped tumours suitable for stereotactic radiotherapy with a linear accelerator are better treated with conformal static non-coplanar beams rather than with the multiple arc technique.
authors.affiliation: Neuro-Oncology Unit, Royal Marsden Hospital, Sutton, Surrey, UK.
authors.forename: R W
authors.initials: RW
authors.lastname: Laing
authors.forename: R E
authors.initials: RE
authors.lastname: Bentley
authors.forename: A E
authors.initials: AE
authors.lastname: Nahum
authors.forename: A P
authors.initials: AP
authors.lastname: Warrington
authors.forename: M
authors.initials: M
authors.lastname: Brada
mesh_terms: D005260:Female; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D008875:Middle Aged; D010315:Particle Accelerators; D011859:Radiography; D011878:Radiotherapy / Q000379:methods*; D013238:Stereotaxic Techniques; D013679:Technology, Radiologic