title: Optimizing collimator margins for isotoxically dose-escalated conformal radiation therapy of non-small cell lung cancer.
abstract: OBJECTIVE
  Isotoxic dose escalation schedules such as IDEAL-CRT [isotoxic dose escalation and acceleration in lung cancer chemoradiation therapy] (ISRCTN12155469) individualize doses prescribed to lung tumors, generating a fixed modeled risk of radiation pneumonitis. Because the beam penumbra is broadened in lung, the choice of collimator margin is an important element of the optimization of isotoxic conformal radiation therapy for lung cancer.
  
  
  METHODS
  Twelve patients with stage I-III non-small cell lung cancer (NSCLC) were replanned retrospectively using a range of collimator margins. For each plan, the prescribed dose was calculated according to the IDEAL-CRT isotoxic prescription method, and the absolute dose (D99) delivered to 99% of the planning target volume (PTV) was determined.
  
  
  RESULTS
  Reducing the multileaf collimator margin from the widely used 7 mm to a value of 2 mm produced gains of 2.1 to 15.6 Gy in absolute PTV D99, with a mean gain ± 1 standard error of the mean of 6.2 ± 1.1 Gy (2-sided P<.001).
  
  
  CONCLUSIONS
  For NSCLC patients treated with conformal radiation therapy and an isotoxic dose prescription, absolute doses in the PTV may be increased by using smaller collimator margins, reductions in relative coverage being offset by increases in prescribed dose.
authors: Department of Oncology, Gray Institute of Radiation Oncology and Biology, University of Oxford, Oxford, UK; Oxford Cancer Centre, Oxford University Hospitals, Oxford, UK. Electronic address: Samantha.warren@oncology.ox.ac.uk.
authors: Samantha
authors: S
authors: Warren
authors: William Buckland Radiotherapy Centre, Alfred Hospital, Commercial Road, Melbourne, Australia.
authors: Vanessa
authors: V
authors: Panettieri
authors: Oxford Cancer Centre, Oxford University Hospitals, Oxford, UK.
authors: Niki
authors: N
authors: Panakis
authors: Oxford Cancer Centre, Oxford University Hospitals, Oxford, UK.
authors: Nicholas
authors: N
authors: Bates
authors: Velindre Cancer Centre, Velindre Road, Whitchurch, Cardiff, UK.
authors: Jason F
authors: JF
authors: Lester
authors: Clatterbridge Cancer Centre, Clatterbridge Road, Wirral, UK.
authors: Pooja
authors: P
authors: Jain
authors: Department of Radiotherapy, Guy's and St. Thomas' NHS Foundation Trust, London, UK.
authors: David B
authors: DB
authors: Landau
authors: Clatterbridge Cancer Centre, Clatterbridge Road, Wirral, UK.
authors: Alan E
authors: AE
authors: Nahum
authors: Clatterbridge Cancer Centre, Clatterbridge Road, Wirral, UK.
authors: W Philip M
authors: WP
authors: Mayles
authors: Department of Oncology, Gray Institute of Radiation Oncology and Biology, University of Oxford, Oxford, UK; Oxford Cancer Centre, Oxford University Hospitals, Oxford, UK.
authors: John D
authors: JD
authors: Fenwick
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D017564:Radiation Pneumonitis / Q000517:prevention & control*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000295:instrumentation* / Q000379:methods*; D012189:Retrospective Studies; D012306:Risk; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome