title: Calculating radiotherapy margins based on Bayesian modelling of patient specific random errors.
abstract: Collected real-life clinical target volume (CTV) displacement data show that some patients undergoing external beam radiotherapy (EBRT) demonstrate significantly more fraction-to-fraction variability in their displacement ('random error') than others. This contrasts with the common assumption made by historical recipes for margin estimation for EBRT, that the random error is constant across patients. In this work we present statistical models of CTV displacements in which random errors are characterised by an inverse gamma (IG) distribution in order to assess the impact of random error variability on CTV-to-PTV margin widths, for eight real world patient cohorts from four institutions, and for different sites of malignancy. We considered a variety of clinical treatment requirements and penumbral widths. The eight cohorts consisted of a total of 874 patients and 27 391 treatment sessions. Compared to a traditional margin recipe that assumes constant random errors across patients, for a typical 4 mm penumbral width, the IG based margin model mandates that in order to satisfy the common clinical requirement that 90% of patients receive at least 95% of prescribed RT dose to the entire CTV, margins be increased by a median of 10% (range over the eight cohorts -19% to +35%). This substantially reduces the proportion of patients for whom margins are too small to satisfy clinical requirements.
authors: Department of Biostatistics and Clinical Trials, Peter MacCallum Cancer Centre, Melbourne, Australia. Faculty of Health Arts and Design, Swinburne University of Technology, Melbourne, Australia.
authors: A
authors: A
authors: Herschtal
authors: L
authors: L
authors: Te Marvelde
authors: K
authors: K
authors: Mengersen
authors: Z
authors: Z
authors: Hosseinifard
authors: F
authors: F
authors: Foroudi
authors: T
authors: T
authors: Devereux
authors: D
authors: D
authors: Pham
authors: D
authors: D
authors: Ball
authors: P B
authors: PB
authors: Greer
authors: P
authors: P
authors: Pichler
authors: T
authors: T
authors: Eade
authors: A
authors: A
authors: Kneebone
authors: L
authors: L
authors: Bell
authors: H
authors: H
authors: Caine
authors: B
authors: B
authors: Hindson
authors: T
authors: T
authors: Kron
mesh_terms: D001499:Bayes Theorem; D015331:Cohort Studies; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D015233:Models, Statistical; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*