title: The validation of tomotherapy dose calculations in low-density lung media.
abstract: The dose-calculation accuracy of the tomotherapy Hi-Art II(R) (Tomotherapy, Inc., Madison, WI) treatment planning system (TPS) in the presence of low-density lung media was investigated. In this evaluation, a custom-designed heterogeneous phantom mimicking the mediastinum geometry was used. Gammex LN300 and balsa wood were selected as two lung-equivalent materials with different densities. Film analysis and ionization chamber measurements were performed. Treatment plans for esophageal cancers were used in the evaluation. The agreement between the dose calculated by the TPS and the dose measured via ionization chambers was, in most cases, within 0.8%. Gamma analysis using 3% and 3 mm criteria for radiochromic film dosimetry showed that 98% and 95% of the measured dose distribution had passing gamma values < or =1 for LN300 and balsa wood, respectively. For a homogeneous water-equivalent phantom, 95% of the points passed the gamma test. It was found that for the interface between the low-density medium and water-equivalent medium, the TPS calculated the dose distribution within acceptable limits. The phantom developed for this work enabled detailed quality-assurance testing under realistic conditions with heterogeneous media.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Summer R
authors.initials: SR
authors.lastname: Chaudhari
authors.forename: Olga L
authors.initials: OL
authors.lastname: Pechenaya
authors.forename: S Murty
authors.initials: SM
authors.lastname: Goddu
authors.forename: Sasa
authors.initials: S
authors.lastname: Mutic
authors.forename: Dharanipathy
authors.initials: D
authors.lastname: Rangaraj
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Bradley
authors.forename: Daniel
authors.initials: D
authors.lastname: Low
mesh_terms: D004938:Esophageal Neoplasms / Q000532:radiotherapy; D005373:Film Dosimetry; D006801:Humans; D008168:Lung / Q000528:radiation effects*; D008482:Mediastinum / Q000528:radiation effects; D008954:Models, Biological; D019047:Phantoms, Imaging; D011786:Quality Control; D011829:Radiation Dosage; D011874:Radiometry; D011878:Radiotherapy / Q000379:methods* / Q000592:standards; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000592:standards; D012680:Sensitivity and Specificity