title: Quantitative analysis of brass compensators for commissioning of the Pinnacle planning system for IMRT.
abstract: Brass compensators for beam modulation present an alternative method for IMRT treatment planning to traditional dynamic leaf modulation. In this work, we present a detailed method to commission the Pinnacle treatment planning system for IMRT using brass compensators. Beam attenuation from various brass thicknesses were measured using an ion chamber, as well as a MapCHECK device, for a representative seven-field IMRT plan. We show that Pinnacle's parameters for compensators can be optimized to match the measured results while still maintaining the original open-beam model. Only Pinnacle's modified scatter factor and brass density value were adjusted. Beam attenuation in several brass slabs were optimized by minimizing a χ(2) function of measured and modeled data for several depths in solid water. Using MapCHECK, Pinnacle's parameters were optimized by minimizing the number of points that fail during a gamma analysis of seven fields in a typical IMRT plan. Our results show that Pinnacle's 10X beam is best modeled using a brass density of 7.8 g/cm(3) and a modified scatter factor of 0.1 cm(-1).
authors.affiliation: Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth. Lawrence.L.Gates@Hitchcock.org.
authors.forename: Larry L
authors.initials: LL
authors.lastname: Gates
authors.forename: David J
authors.initials: DJ
authors.lastname: Gladstone
mesh_terms: D000465:Algorithms; D003300:Copper; D006801:Humans; D021621:Imaging, Three-Dimensional; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000706:statistics & numerical data; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000706:statistics & numerical data; D012984:Software; D015032:Zinc
chemical_list: C048399:brass; D003300:Copper; D015032:Zinc