Determination of Planning Target Volume in Radiotherapy - A Review

Treatment volume definitions used in three-dimensional radiotherapy treatment planning are essential in advancing treatment modalities. However, there are many sources of error during the treatment preparation and execution that limit the accuracy. Consequently, a safety margin is required to add to the target to ensure that the planned dose is delivered to the target. Multiple margins surround the tumour to reduce positional inaccuracy, such as Clinical Target Volume (CTV), Planning Target Volume (PTV), etc. The International Commission of Units and Measurement (ICRU) recommended margins in 1978. It was later reviewed in Reports 50 and 62 of ICRU, providing information on margins covering gross volume, clinical volume, and critical structures that should be eliminated as feasible. This article aims to discuss various techniques and methods that various authors have created. Keywords: Margin, Errors, GTV, CTV, ITV, PTV, ICRU 50, ICRU 62, Radiotherapy.