Dose-volume histogram

Dose-volume histogram (DVH) is a graphical representation used in radiation therapy to correlate volumes of tissue with a specific dose of radiation. The DVH is a crucial tool in the planning and evaluation of radiation treatments, allowing for the optimization of dose distributions to tumor targets while minimizing exposure to surrounding healthy tissues. Understanding the DVH is essential for radiation oncologists, medical physicists, and dosimetrists in the design of effective and safe radiation treatment plans.

Overview

A dose-volume histogram displays two key pieces of information: the dose of radiation and the volume of tissue receiving that dose. On the graph, the dose is typically represented on the x-axis, and the volume is represented on the y-axis, which can be expressed either as an absolute volume (in cubic centimeters) or as a percentage of the total volume. The curve on the graph shows the percentage of a given volume that receives a specific dose or higher, providing a comprehensive overview of the dose distribution within the target area and surrounding tissues.

Importance in Radiation Therapy

The primary goal of radiation therapy is to deliver a lethal dose of radiation to cancerous cells while sparing the surrounding healthy tissue. The DVH is instrumental in achieving this goal, as it provides a visual summary of the dose distribution across the treatment volume. By analyzing the DVH, clinicians can assess the uniformity of the dose within the target area, identify areas of under or overdosage, and evaluate the risk of radiation-induced side effects based on the dose received by critical structures.

Components of a DVH

A typical DVH includes several components:

• Cumulative DVH: Shows the cumulative volume of tissue receiving a given dose or higher. It is the most common type of DVH used in treatment planning.
• Differential DVH: Displays the differential volume of tissue receiving a specific dose range, offering insight into the dose gradient across the treatment volume.
• Mean Dose: The average dose received by the volume of interest.
• Dose Homogeneity Index (DHI): A measure of how uniformly the dose is distributed within the target volume.
• Vx: Represents the volume of tissue receiving x Gy of radiation or more. For example, V20 would indicate the volume of tissue receiving 20 Gy or higher.
• Dx: Indicates the dose received by x% of the volume. For instance, D95 would represent the dose received by 95% of the volume.

Applications

DVHs are used in various aspects of radiation therapy planning and evaluation:

• Treatment Planning: DVHs help in comparing different treatment plans to select the one that offers the best trade-off between treating the tumor and sparing normal tissues.
• Dose Optimization: By analyzing DVHs, clinicians can adjust treatment parameters to improve dose distribution.
• Quality Assurance: DVHs serve as a tool for verifying that the delivered dose matches the planned dose.
• Research and Development: DVH analysis is used in clinical studies to correlate dose distributions with treatment outcomes and side effects.

Limitations

While DVHs provide valuable information about dose distribution, they have limitations:

• They do not provide spatial information about where the dose is delivered within the volume.
• They may not fully capture the complexity of dose distributions, especially in heterogeneous tissues.
• Interpretation of DVHs requires expertise and understanding of the clinical context.

Conclusion

The dose-volume histogram is a fundamental tool in radiation therapy, enabling the optimization of treatment plans for the effective and safe delivery of radiation doses. By providing a detailed overview of dose distribution, DVHs assist clinicians in making informed decisions to achieve the best possible outcomes for patients undergoing radiation therapy.