Absorbed dose uncertainties in external radiotherapy and their relation to treatment plan complexity

Abstract

The purpose of this work was to investigate absorbed dose uncertainties, i.e., differences between planned and delivered dose in external radiotherapy, arising from various sources and their relationship with treatment plan complexity. Thirty-six volumetric modulated arc therapy plans, representing different treatment sites and levels of complexity, were included. Across four studies, different aspects of treatment plan complexity and absorbed dose uncertainty were analyzed by calculating complexity metrics, performing measurements, and conducting simulations. The results showed that the different aspects of plan complexity are not always strongly correlated and can influence dose uncertainties in different ways. Uncertainties arising from delivery variations were generally smaller in magnitude than those related to dose calculations. A novel method called 3DUM was developed to translate plan complexity related to the field edge, into a spatially resolved, voxel-based representation. This method revealed that regions with increased probability of dose uncertainties commonly occur near and outside the tumor volume. The findings in this thesis highlight that understanding the spatial characteristics of dose uncertainties and the different aspects of plan complexity plays a key role in reliable treatment evaluation.