Motion in radiotherapy: particle therapy

Charged particle beam radiotherapy requires dedicated measures to compensate for the dosimetric influence of inter- and intra-fractional target motion. Independent of the delivery technique, these measures have to incorporate the strong influence of the radiological depth on the delivered dose. For scanned beam delivery, interference effects of target motion and scanned beam can further cause under-dosage of the clinical target volume despite using margins. Within the scope of this review, published data with respect to motion management in scattered as well as scanned beam treatment delivery will be summarized. Based on a section covering the dosimetric impact of organ motion, motion management during treatment planning, patient positioning, treatment delivery and treatment validation will be summarized. For scattered beam delivery, the concepts and data are often based on clinical usage since treatment of moving tumors has been performed for several years. In the field of scanned beam delivery, the report focuses on the results of research on countermeasures of the interference effect. Clinical application of these techniques can be expected in the near future.