Management of Respiratory-Induced Tumour Motion for Tailoring Target Volumes during Radiation Therapy

Radiotherapy is one of the main treatment modalities in modern day’s oncology practice and is used to treat tumours in up to 50% of all cancer patients. The key to successful delivery of a high radiation dose to the tumour without causing unacceptable toxicity of normal tissues is the use of treatment fractionation. During fractionated radiotherapy, it is of importance to reduce inter- and intra-fraction geometrical uncertainties in order to ensure adequate dose delivery to the tumour and preventing unnecessary irradiation of normal tissues. Geometrical uncertainties can be the result of many different factors, including patient set-up, mechanical errors, patient or organ motion, and anatomical changes during the course of treatment. Of these factors, respiratory induced organ motion significantly contributes to geometrical uncertainties during radiotherapy. Therefore, adequate management of moving targets during radiotherapy contributes to the reduction of geometrical uncertainties in radiotherapy planning and improves accuracy of dose delivery. Many technological solutions have been developed for management of respiratory motion during radiotherapy. These include the use of different planning methods in combination with conventional radiotherapy techniques, respiratory gated radiotherapy, and real-time tumour tracking approaches. This chapter will provide an overview of the most important radiotherapy strategies to account for organ motion due to patient respiration. Different technical considerations and solutions regarding respiratory motion management during all the steps of radiotherapy workflow will be discussed.