title: Effects of averaging over motion and the resulting systematic errors in radiation therapy.
abstract: The potential for systematic errors in radiotherapy of a breathing patient is considered using the statistical model of Bortfeld et al (2002 Phys. Med. Biol. 47 2203-20). It is shown that although averaging over 30 fractions does result in a narrow Gaussian distribution of errors, as predicted by the central limit theorem, the fact that one or a few samples of the breathing patient's motion distribution are used for treatment planning (in contrast to the many treatment fractions that are likely to be delivered) may result in a much larger error with a systematic component. The error distribution may be particularly large if a scan at breath-hold is used for planning.
authors.affiliation: Joint Physics Department, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey SM2 5PT, UK. phil.evans@icr.ac.uk
authors.forename: Philip M
authors.initials: PM
authors.lastname: Evans
authors.forename: Catherine
authors.initials: C
authors.lastname: Coolens
authors.forename: Elena
authors.initials: E
authors.lastname: Nioutsikou
mesh_terms: D006801:Humans; D015233:Models, Statistical; D009038:Motion; D009068:Movement; D016011:Normal Distribution; D019047:Phantoms, Imaging; D011336:Probability; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012119:Respiration