Set-up error & organ motion uncertainty: a review

Abstract

Conformal radiotherapy allows improvement in the treatment outcome due to increased targeting accuracy through advanced beam shaping techniques to precisely conform radiation dose to the geometry of the tumour. Treatment set-up and organ motion uncertainties are unavoidable factors that are limiting increases in accuracy and have to be accounted for in conformal treatment planning. The magnitudes of set-up errors and organ motion uncertainties for specific sites, and using various set-up techniques, have been quantified in the literature. However, the parameters used with these measurements and the presentation of the data has differed between studies for the same site. The purpose of this paper is to analyse and combine the published material into a uniform format and to display typical reported values of set-up and organ motion uncertainties. Values measured under similar conditions were averaged across studies. The results of this analysis illustrate (1) variability in the parameters used for measurements across studies, (2) typical motion ranges of the prostate, kidneys, liver and diaphragm, (3) typical means and standard deviations for set-up errors associated with the prostate, pelvis, brain, head and neck, thorax, rectum and breast and (4) a brief review of the common methods to lower or account for these uncertainties.