title: A simulation of the effects of set-up error and changes in breast volume on conventional and intensity-modulated treatments in breast radiotherapy.
abstract: The effect of interfractional patient movement on dosimetry has been investigated for breast radiotherapy. Errors in patient set-up and changes in breast volume were simulated individually to determine how each contributes to the total dosimetric error. Two treatment techniques were investigated: a conventional treatment and an intensity-modulated treatment delivered using compensators. Six patients were investigated and anterior-posterior (AP) and superior-inferior (SI) displacements were simulated by displacing the isocentre in both directions by 2, 5 and 10 mm. A model of the breast was developed from the six patients to simulate changes in breast volume. In this model, the breast was described as a set of semi-ellipses. The volume of the breast was changed by varying the magnitude of the semi-major and semi-minor axes. Anisotropic changes in breast volume were also investigated. The dosimetric error was evaluated for each dose plan by calculating the volume outside the 95-105% dose range resulting from the simulations. A number of parameters describing the size and shape of the breast were also investigated to determine whether a susceptibility of outline sets to interfractional patient movement could be predicted. A parameter describing the increase in the breast volume outside the 95-105% dose range was calculated for AP a
authors.affiliation: Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Sutton, Surrey, UK.
authors.forename: C
authors.initials: C
authors.lastname: Hector
authors.forename: S
authors.initials: S
authors.lastname: Webb
authors.forename: P M
authors.initials: PM
authors.lastname: Evans
mesh_terms: D001940:Breast / Q000033:anatomy & histology*; D001943:Breast Neoplasms / Q000532:radiotherapy*; D003198:Computer Simulation; D005260:Female; D006801:Humans; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted; D015203:Reproducibility of Results