title: Utility of megavoltage fan-beam CT for treatment planning in a head-and-neck cancer patient with extensive dental fillings undergoing helical tomotherapy.
abstract: The purpose of this study was to demonstrate the potential utility of megavoltage fan-beam computed tomography (MV-FBCT) for treatment planning in a patient undergoing helical tomotherapy for nasopharyngeal carcinoma in the presence of extensive dental artifact. A 28-year-old female with locally advanced nasopharyngeal carcinoma presented for radiation therapy. Due to the extensiveness of the dental artifact present in the oral cavity kV-CT scan acquired at simulation, which made treatment planning impossible on tomotherapy planning system, MV-FBCT imaging was obtained using the HI-ART tomotherapy treatment machine, with the patient in the treatment position, and this information was registered with her original kV-CT scan for the purposes of structure delineation, dose calculation, and treatment planning. To validate the feasibility of the MV-FBCT-generated treatment plan, an electron density CT phantom (model 465, Gammex Inc., Middleton, WI) was scanned using MV-FBCT to obtain CT number to density table. Additionally, both a "cheese" phantom (which came with the tomotherapy treatment machine) with 2 inserted ion chambers and a generic phantom called Quasar phantom (Modus Medical Devices Inc., London, ON, Canada) with one inserted chamber were used to confirm dosimetric accuracy. The MV-FBCT could be used to clearly visualize anatomy in the region of the dental artifact and provide sufficient soft-tissue contrast to assist in the delineation of normal tissue structures and fat planes. With the elimination of the dental artifact, the MV-FBCT images allowed more accurate dose calculation by the tomotherapy system. It was confirmed that the phantom material density was determined correctly by the tomotherapy MV-FBCT number to density table. The ion chamber measurements agreed with the calculations from the MV-FBCT generated phantom plan within 2%. MV-FBCT may be useful in radiation treatment planning for nasopharyngeal cancer patients in the setting of extensive dental artifacts.
authors.affiliation: Department of Radiation Oncology, University of California Davis School of Medicine, Sacramento, USA.
authors.forename: Claus
authors.initials: C
authors.lastname: Yang
authors.forename: Tianxiao
authors.initials: T
authors.lastname: Liu
authors.forename: Richard L
authors.initials: RL
authors.lastname: Jennelle
authors.forename: Janice K
authors.initials: JK
authors.lastname: Ryu
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Vijayakumar
authors.forename: James A
authors.initials: JA
authors.lastname: Purdy
authors.forename: Allen M
authors.initials: AM
authors.lastname: Chen
mesh_terms: D000328:Adult; D016477:Artifacts; D002277:Carcinoma / Q000000981:diagnostic imaging* / Q000628:therapy; D015921:Dental Implants; D005260:Female; D006801:Humans; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging* / Q000628:therapy; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted; D036542:Tomography, Spiral Computed
chemical_list: D015921:Dental Implants