DoseVolume

Dosevolume is a concept used in radiotherapy to describe how radiation dose is distributed within a defined volume, such as a target tumor or an organ at risk. It summarizes the relationship between dose and volume for a structure and is essential for planning and evaluating treatment.

A dose-volume histogram (DVH) is the primary tool for illustrating dose-volume relationships. DVHs can be presented as cumulative or differential. A cumulative DVH shows, for each dose level, the fraction or percentage of the structure that receives at least that dose. A differential DVH shows the amount of volume receiving specific dose intervals. From DVHs, common metrics are derived using two notations: Vx and Dx. Vx denotes the volume percentage receiving at least x Gy (for example, V20 Gy for the lung). Dx denotes the dose that covers x% of the structure (for example, D95% is the dose received by 95% of the structure).

In clinical practice, dosevolume metrics guide planning decisions. Target coverage is often assessed with metrics like V95% for the planning target volume (PTV), while organs at risk are constrained with limits such as V20 Gy for lung tissue or Dmax for the spinal cord. DVHs are widely used to compare competing plans and to communicate constraints, but they do not convey spatial information about where doses are delivered within a structure. Therefore, DVHs are complemented by 3D dose distributions and isodose visualizations. Limitations include interpolation, anatomical changes during treatment, and uncertainties in dose calculation, which can affect the interpretation of dose-volume statistics.