title: The importance of three-dimensional brachytherapy treatment planning for nasopharyngeal carcinoma.
abstract: High dose rate (HDR) intracavitary brachytherapy is now more frequently incorporated into treatment programmes for patients with persistent and recurrent nasopharyngeal carcinoma (NPC). However, many centres still employ two-dimensional (2-D) image reconstruction for applicators with a three-dimensional (3-D) orientation. In this study, we introduced the use of a mobile modified Nucletron reconstruction box inside the brachytherapy suite for image reconstruction and quality assurance. Three-dimensional reconstruction of the applicators' configurations proved possible and the dose distributions generated by the 2-D and 3-D image reconstructions could be compared. Thirty-one applications were included in this part of the analysis. The results showed that, based on the 2-D planning method, the reference doses were under-prescribed by 1%-10% in all except one patient, whose dose was over-prescribed by 3%. The evaluated doses to the floor of the sphenoid, which was shown to be significant for subsequent local control, was shown to be underestimated by up to 19% or overestimated by 18%, with an average of 5.9% dose underestimation. With this system, the reliability of the anchoring techniques was verified by posttherapy radiographs. Any catheter displacement of more than 1 mm was counted as a failure. Nine of the 43 verified applications were classified as failures, although six of nine catheter displacements measured < or = 2.5 mm. We recommend the routine use of a modified reconstruction box for 3-D image reconstruction for dose calculation and prescription in the treatment of NPC with HDR intracavitary brachytherapy. Quality assurance programmes should be included as an integral part of any HDR treatment; their importance cannot be overemphasized.
authors.affiliation: Tuen Mun Hospital, Hong Kong.
authors.forename: T W
authors.initials: TW
authors.lastname: Leung
authors.forename: V Y
authors.initials: VY
authors.lastname: Wong
authors.forename: S Y
authors.initials: SY
authors.lastname: Tung
authors.forename: C M
authors.initials: CM
authors.lastname: Lui
authors.forename: W W
authors.initials: WW
authors.lastname: Tsang
authors.forename: W K
authors.initials: WK
authors.lastname: Sze
authors.forename: S K
authors.initials: SK
authors.lastname: O
mesh_terms: D001918:Brachytherapy; D006801:Humans; D008953:Models, Anatomic; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted