title: Dosimetric analysis of isocentrically shielded volumetric modulated arc therapy for locally recurrent nasopharyngeal cancer.
abstract: This study aimed to investigate the dosimetric characteristics of an isocentrically shielded RapidArc (IS-RA) technique for treatment of locally recurrent nasopharyngeal cancer (lrNPC). In IS-RA, the isocenter was placed at the center of the pre-irradiated brainstem (BS)/spinal cord (SC) and the jaws were set to shield the BS/SC while ensuring the target coverage during the whole gantry rotation. For fifteen patients, the IS-RA plans were compared with the conventional RapidArc (C-RA) regarding target coverage, organ-at-risk (OAR) sparing and monitor units (MUs). The relationship between the dose reduction of BS/SC and some geometric parameters including the angle extended by the target with respect to the axis of BS/SC (Ang_BSSC), the minimum distance between the target and BS/SC (Dist_Min) and the target volume were evaluated. The IS-RA reduced the BS/SC doses by approximately 1-4 Gy on average over the C-RA, with more MUs. The IS-RA demonstrated similar target coverage and sparing of other OARs except for slightly improved sparing of optic structures. More dose reduction in the isocentric region was observed in the cases with larger Ang_BSSC or smaller Dist_Min. Our results indicated that the IS-RA significantly improves the sparing of BS/SC without compromising dosimetric requirements of other involved structures for lrNPC.
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Jia-Yang
authors.initials: JY
authors.lastname: Lu
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Bao-Tian
authors.initials: BT
authors.lastname: Huang
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Xing
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Chang
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Xun
authors.initials: X
authors.lastname: Peng
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Liang-Xi
authors.initials: LX
authors.lastname: Xie
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Zhi-Xiong
authors.initials: ZX
authors.lastname: Lin
authors.affiliation: Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Li
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012008:Recurrence; D055815:Young Adult