title: An assessment of the magnitude of intra-fraction movement of head-and-neck IMRT cases and its implication on the action-level of the imaging protocol.
abstract: OBJECTIVE
  A planning margin ⩽3 mm is employed in some head-and-neck IMRT cases due to the proximity of critical structures. This study aims to explore the need to redefine the action-level in the head-and-neck imaging protocol in consideration of the intra-fraction movement.
  
  
  METHODS
  This is a local study of 18 patients treated using the same immobilisation system and setup protocol. Post-treatment orthogonal pair of kilovoltage X-ray images was acquired on the first three days of treatment. 106 sets of pre- and post-treatment kV X-ray images acquired over 53 fractions were analysed against the treatment planning DRR for calculation of intra-fraction movement.
  
  
  RESULTS
  Individual mean intra-fraction movement in all directions ranged from -1.8 to 1.1 mm. Population mean (median) intra-fraction movement in the x-, y-, and z-planes were -0.1 mm (0 mm), -0.3 mm (-0.3 mm) and -0.2 mm (-0.2 mm) respectively. Intra-fraction movement in all three dimensions, x-, y- and z-planes were considered statistically significant (p<0.05). 7 out of 53 fractions (13.2%) were highlighted as the combined magnitude of the intra-fraction motion with the uncorrected pre-treatment setup errors had exceeded the boundaries of given margins.
  
  
  CONCLUSIONS
  3 mm-AL was not adequate to account for intra-fraction movement when the CTV-PTV margin was ⩽3 mm and should be excluded from the routine imaging protocol and daily image-guided radiotherapy should be employed. Adjusting the action-level to 2 mm would allow a more confident approach in delivery of the prescribed dose in head-and-neck IMRT cases.
authors.affiliation: School of Radiography, Kingston University & St George's, University of London, Surrey, United Kingdom; Division of Radiation Oncology, National Cancer Centre Singapore, Singapore. Electronic address: eric.pang.p.p@nccs.com.sg.
authors.forename: Pei Ping Eric
authors.initials: PP
authors.lastname: Pang
authors.affiliation: School of Radiography, Kingston University & St George's, University of London, Surrey, United Kingdom.
authors.forename: Julie
authors.initials: J
authors.lastname: Hendry
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Shie Lee
authors.initials: SL
authors.lastname: Cheah
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Yoke Lim
authors.initials: YL
authors.lastname: Soong
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Kam Weng
authors.initials: KW
authors.lastname: Fong
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Tien Seng Joseph
authors.initials: TS
authors.lastname: Wee
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Wee Kiat Terence
authors.initials: WK
authors.lastname: Tan
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Wen Long
authors.initials: WL
authors.lastname: Nei
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Fuqiang
authors.initials: F
authors.lastname: Wang
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Ru Xin
authors.initials: RX
authors.lastname: Wong
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Wee Loon
authors.initials: WL
authors.lastname: Ng
authors.affiliation: Division of Radiation Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: John
authors.initials: J
authors.lastname: Chen
mesh_terms: D000328:Adult; D000368:Aged; D003287:Contrast Media; D005260:Female; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007103:Immobilization; D008297:Male; D008875:Middle Aged; D009068:Movement; D011446:Prospective Studies; D011856:Radiographic Image Enhancement / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D003287:Contrast Media
keywords: Action-level; Correction strategies; Head and neck; Imaging protocol; Intra-fraction; Planning margins