Review of technologies and procedures of clinical dosimetry for scanned ion beam radiotherapy.

In the last few years, the use of ions in radiation therapy is gaining interest and it is being considered medically necessary for a growing subset of tumours. Concurrently, the technologies involved in a particle therapy treatment are rapidly evolving, as well as the accuracy in the dose delivery in spite of the increased complexity. Since nowadays, the pencil beam scanning technique is showing very interesting features in terms of dose conformation and overall treatment outcome, the present review is intended to summarize the main procedures, detectors and tools adopted for the clinical dose verification. A list of dose measurements is provided, with the aim of being a valuable guidance for starting and future particle therapy facilities. Absorbed dose to water, relative dose, fluence and surrogates of the delivered dose are the main quantities measured by means of different detectors, specifically developed for point-like, 1D or 2D measurements. The dosimetric procedures are here categorized according to their purpose, distinguishing between system commissioning and clinical quality assurance. A separate discussion is dedicated to patient specific, in vivo and 4D dose verification, which aim at assessing the actual delivered dose. Together with the description of the currently used methods, challenges and perspectives toward an increasingly accurate and fast dose verification strategy are discussed.