Precision and uncertainties for moving targets

Abstract

This chapter discusses time-dependent variations of the target location and the patient's density distribution and its consequences during proton therapy treatments. Variations can occur on different timescales; i.e., over the entire treatment course (weight loss/gain, treatment response of the target), between subsequent treatment fractions (interfractional motion like setup variations or changes in cavity fillings), and within a treatment fraction (intrafractional motion due to heartbeat, breathing, or relaxation). This chapter mainly focuses on intrafractional motion. At the moment, motion in proton radiotherapy is a problem that has not yet been completely solved. A variety of strategies have been discussed to mitigate the effects of motion in proton radiotherapy. The best approach to deal with motion will depend on the tumor sites and the configuration of a specific proton treatment facility, and is likely a combination of strategies discussed in this chapter. First clinical experience indicates that previous in silico studies might have overestimated the dosimetric impact of motion by investigating its effects individually instead of embedded in realistic treatment scenarios. This chapter reviews the research and summarizes the current clinical practice related to the treatment of moving targets with proton therapy.