A dose-volume histogram (DVH) is a

histogram A histogram is a visual representation of the frequency distribution, distribution of quantitative data. To construct a histogram, the first step is to Data binning, "bin" (or "bucket") the range of values— divide the entire range of values in ...

relating

radiation dose Ionizing (ionising) radiation, including nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionize atoms or molecules by detaching electrons from them. Some pa ...

to tissue

volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...

radiation therapy Radiation therapy or radiotherapy (RT, RTx, or XRT) is a therapy, treatment using ionizing radiation, generally provided as part of treatment of cancer, cancer therapy to either kill or control the growth of malignancy, malignant cell (biology), ...

planning. DVHs are most commonly used as a plan evaluation tool and to compare doses from different plans or to structures. DVHs were introduced by Michael Goitein (who introduced radiation therapy concepts such as the "beam's-eye-view," "digitally reconstructed radiograph," and uncertainty/error in planning and positioning, among others) and Verhey in 1979. DVH summarizes 3D dose distributions in a graphical 2D format. In modern radiation therapy, 3D dose distributions are typically created in a computerized treatment planning system (TPS) based on a 3D reconstruction of a CT scan. The "volume" referred to in DVH analysis is a target of radiation treatment, a healthy organ nearby a target, or an arbitrary structure.

Types

DVHs can be visualized in either of two ways: differential DVHs or cumulative DVHs. A DVH is created by first determining the size of the dose bins of the histogram. Bins can be of arbitrary size, 0.005 Gy, 0.2 Gy or 1 Gy for instance. The size is often a matter of tradeoff between accuracy and computational or memory cost (if we store the DVH in a database). In a differential DVH, bar or column height indicates the volume of structure receiving a dose given by the bin. Bin doses are along the horizontal axis, and structure volumes (either percent or absolute volumes) are on the vertical. The differential DVH takes the appearance of a typical

. The total volume of the

organ Organ and organs may refer to: Biology * Organ (biology), a group of tissues organized to serve a common function * Organ system, a collection of organs that function together to carry out specific functions within the body. Musical instruments ...

that receives a certain dose is plotted in the appropriate dose bin. This volume is determined by the total number of

voxel In computing, a voxel is a representation of a value on a three-dimensional regular grid, akin to the two-dimensional pixel. Voxels are frequently used in the Data visualization, visualization and analysis of medical imaging, medical and scient ...

s characterized by a specified range of dosage for the organ considered. The differential DVH provides information about changes in dose within the structure considered as well as visualization of minimum and maximum dose. The cumulative DVH is plotted with bin doses along the horizontal axis, as well. However, the column height of the first bin (e.g.,

, 1 The comma is a punctuation mark that appears in several variants in different languages. Some typefaces render it as a small line, slightly curved or straight, but inclined from the vertical; others give it the appearance of a miniature fille ...

nbsp;Gy) represents the volume of structure receiving a dose greater than or equal to that dose. The column height of the second bin (e.g., (1, 2] Gy) represents the volume of structure receiving greater than or equal to that dose, etc. With very fine (small) bin sizes, the cumulative DVH takes on the appearance of a smooth line graph. The lines always slope and start from top-left to bottom-right. For a structure receiving a very homogeneous dose (100% of the volume receiving exactly 10 Gy, for example) the cumulative DVH will appear as a horizontal line at the top of the graph, at 100% volume as plotted vertically, with a vertical drop at 10 Gy on the horizontal axis. Cumulative dose-volume histogram

A DVH used clinically usually includes all structures and targets of interest in the

radiotherapy Radiation therapy or radiotherapy (RT, RTx, or XRT) is a treatment using ionizing radiation, generally provided as part of cancer therapy to either kill or control the growth of malignant cells. It is normally delivered by a linear particle ...

plan, each line plotted a different color, representing a different structure. The vertical axis is almost always plotted as percent volume (rather than absolute volume), as well.

Drawbacks

Clinical studies have shown that DVH metrics correlate with patient toxicity outcomes. A drawback of the DVH methodology is that it offers no spatial information; i.e., a DVH does not show where within a structure a dose is received. Also, DVHs from initial radiotherapy plans represent the doses to structures at the start of radiation treatment. As treatment progresses and time elapses, if there are changes (i.e. if patients lose weight, if tumors shrink, if organs change shape, etc.), the original DVH loses its accuracy.

References

External links

*{{cite web, last1=Sambasivam, first1=Sasikumar, title=Dose Volume Histogram, url=http://www.slideshare.net/sasikumars/dose-volume-histogram, website=Slideshare, page=28, format=Slides, date=April 2014 Radiation therapy Medical physics