title: Fluoroscopy as a surrogate for lung tumour motion.
abstract: OBJECTIVE
  The aim of this article was to test a simple approach of using pixel density values from fluoroscopy images to enable gated radiotherapy.
  
  
  METHODS
  Anterior and lateral (LAT) from images were acquired from 18 patients referred for radical radiotherapy for non-small cell lung cancer for a period of 30-45 s. The amplitude of movement and the number of breathing cycles were determined in the right-left (RL) and superoinferior (SI) directions on the anterior images and the anteroposterior (AP) and SI directions on the lateral images. The breathing pattern was created by analysing the variation in a summation of pixel values within a defined area. The greatest and lowest 30% of pixel values were set as the duty cycle to represent inhale and exhale amplitude-based gating.
  
  
  RESULTS
  A median of eight breathing cycles was captured for each patient with a duration of 2.2-11.8 s per cycle. The mean (range) motion was 4.7 mm (2.4-5.8 mm), 7.2 mm (2.3-17.6 mm), 6.2 mm (1.9-13.8 mm) and 4.8 mm (2.4-11.3 mm) in the RL, SI (AP), SI (LAT) and AP directions, respectively. A total of 10/14 anterior videos and 7/11 LAT videos had correlations between motion and breathing of >0.6. Margins of 5.5 mm, 6.8 mm and 6.6 mm in the RL, SI and AP directions, respectively, were determined to gate in exhale. The benefit of gating was greater when motion was >5 mm.
  
  
  CONCLUSIONS
  The simple approach of using pixel density values from fluoroscopy images to distinguish inhale from exhale and enable gating was successfully applied in all patients. This technique may potentially provide an accurate surrogate for tumour position.
authors.affiliation: Radiotherapy Department, Royal Marsden NHS Foundation Trust and Institute of Cancer Research, Sutton, UK. Helen.McNair@rmh.nhs.uk
authors.forename: H A
authors.initials: HA
authors.lastname: McNair
authors.forename: A
authors.initials: A
authors.lastname: Kavanagh
authors.forename: C
authors.initials: C
authors.lastname: Powell
authors.forename: J R N
authors.initials: JR
authors.lastname: Symonds-Tayler
authors.forename: M
authors.initials: M
authors.lastname: Brada
authors.forename: P M
authors.initials: PM
authors.lastname: Evans
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D045853:Exhalation / Q000502:physiology; D005471:Fluoroscopy; D006801:Humans; D001239:Inhalation / Q000502:physiology; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013997:Time Factors