Conventional modern radiotherapy has become highly efficient and less toxic, due to better tumor targeting and conformity of dose delivery, permitting sparing of healthy organs while achieving dose escalation in the tumor. Targeting a tumor surrounded by normal tissue within a living human body comes with the challenge of delivering the correct dose of ionizing radiation within a given time, usually of several minutes, while taking into account movement, of which the most important is due to breathing.

Respiratory motion management has been a recognized challenge in the field of radiation oncology as tumors, especially in the thorax and upper abdomen, are in constant motion. Throughout the years, many techniques have become standard in the clinic to assure accurate targeting during tumor motion while minimizing the dose delivered to healthy organs. The use of four-dimensional CT scans in the simulation process is now ubiquitous and allows for the summation of the target position in all breathing phases, or alternatively limiting the treatment to preselected breathing phases only. Motion can be mitigated by abdominal compression, or by asking patients to hold their breath. These techniques have brought considerable improvements in clinical outcomes, nevertheless they can be improved upon as they still require considerable margins to assure accuracy, respiratory motion being potentially irregular and tumor motion even more so.

This narrative review, beyond describing standard of care respiratory motion management methods, seeks to go through the innovations developed in the field in the last ten years. It discusses techniques that allow continuous assessment of tumor and organ movement such as electromagnetic transponder fiducials, MRI-guided radiation therapy, showing that respiratory movement is more complex and variable than initially believed. Novel techniques that allow extended deep-inspiration breath-holds, that can last over 5 minutes are discussed. CPAP machines and mechanical ventilators, used to regularize and stabilize respiratory movements, as well as high-frequency non-invasive ventilation, allowing apnea-like breath suppression for over 20 minutes are presented. As a future perspective, ultra-fast treatment delivery with FLASH radiotherapy, which may shake up the field entirely, is overviewed.