Defining the tumour and target volumes for radiotherapy

Review of the ICRU target-volume concepts. It summarizes ICRU Report 62's internal margin (for variations in the size, shape and position of the CTV, for example from organ filling or respiration) and set-up margin, and its planning organ at risk volume (PRV): a margin around an organ at risk, analogous to the PTV margin, because systematic and random errors apply to organs at risk as much as to the CTV. It notes that a PRV substantially enlarges the organ and may create dilemmas with target dose, so it is needed only in certain circumstances — around organs whose damage is especially dangerous, such as the spinal cord, a "serial" tissue. Full text read in Europe PMC (PMC1434601).

A clear, open-access explanation of the ICRU volumes — GTV, CTV, PTV, the internal and set-up margins, and the PRV — and when a PRV is worth adding.