A simulation technique for computation of the dosimetric effects of setup, organ motion and delineation uncertainties in radiotherapy

In this study, we introduce a novel simulation technique to incorporate delineation errors into radiotherapy treatment margins and combine them with organ motion and set-up errors to investigate the cumulative dosimetric effects in different tumour sites. The effects of applying patient realignment correction protocols for radical treatments of prostate, lung and brain tumours were also modelled. Simulations were based on data from measurements using image-guidance techniques, including the use of fiducial markers in prostate and breathing correction techniques for the lung. The use of different sizes of planning target volume (PTV) margins was also evaluated. The prostate clinical target volumes’ V99% showed up to 3.2% improvement with reduction in treatment uncertainties. For the lung plans, the V99% increased by up to an average of 10% with increase in treatment margin size from 0.5 to 1.5 cm. This improvement was, however, at the detriment of the dose delivered to the critical organs where the maximum dose received by the spinal cord increased by up to 0.5 Gy per fraction. These results were used to deduce the possible margin reductions and dose escalation achievable with reduced uncertainties. Keywords: Monte Carlo simulation Radiotherapy Motion correction Radiation planning Treatment margins