![Intro
• To form a DVH for any 3D object, one looks at the dose value
for each voxel in the object and forms a histogram,
counting the number of voxels that receive each different
dose level
• Because the volume of each voxel is known, the volume of the
organ receiving each dose level is known.
• Both the volume (vertical) and dose (horizontal) axes can be
displayed in absolute terms (as cubic centimeters [cc] or
Gray [Gy]) or in relative terms (% volume or % dose),
depending on how the planner wants to analyze the results.](https://image.slidesharecdn.com/dose-volumehistogram-140418211725-phpapp02/75/Dose-volume-histogram-8-2048.jpg)
Uploaded bySasikumar Sambasivam
Dose volume histogram
This document discusses dose-volume histograms (DVHs) which are used to analyze and compare radiation dose distributions in radiotherapy treatment planning. It describes how DVHs are generated by counting the number of voxels receiving different dose levels. DVHs can be displayed cumulatively or differentially and show the volume of structures receiving particular doses. The document outlines some limitations of DVHs including their insensitivity to small hot or cold spots and lack of spatial information. It emphasizes that DVHs should be used along with visual analysis of dose distributions and dose-volume statistics when evaluating treatment plans.
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Dose volume histogram
- 1. Dose-Volume Histogram Dr SasikumarSambasivam
- 2. • A voxelrepresents a value on a regular grid in three- dimensional space. • Voxel is a combination of "volume" and "pixel" where pixel is a combination of "picture" and "element"
- 3. Intro • The displayand analysis of dose distribution Displaying dose – Colour scales – Dose banding – Interactivity Dose volume histograms – Types – Calculation and interpretation – Problems and pitfalls
- 4.
- 5. Methods of displayingdose • 1. Iso-dose contours Sets of closed contours linking voxels of equal dose • 2. Colour wash The coding of CT and dose in the same voxel through the modulation of both intensity (CT) and colour (dose) • 3. Iso-dose surfaces The shaded surface (pseudo-3d) representation of a particular dose level and selected VOIs
- 8. Intro • To forma DVH for any 3D object, one looks at the dose value for each voxel in the object and forms a histogram, counting the number of voxels that receive each different dose level • Because the volume of each voxel is known, the volume of the organ receiving each dose level is known. • Both the volume (vertical) and dose (horizontal) axes can be displayed in absolute terms (as cubic centimeters [cc] or Gray [Gy]) or in relative terms (% volume or % dose), depending on how the planner wants to analyze the results.
- 10. • DVHs aredisplayed in : • cumulative, • and differential
- 11. The differential histogram •The generic form of any histogram, displaying the volume of the organ that receives dose within each dose bin (1% or 0.5 to 1 Gy is a typical dose bin width). • It is useful for display of the dose-to-target volumes, because one can easily visualize the minimum dose, the maximum dose, and the dose most representative of the dose to the entire target volume
- 12. • This typeis necessary in order to appropriately compare DVHs formed with different dose bin sizes, because the volume contained in any dose bin changes as the dose bin size changes. • The differential DVH plots (1/Dbin) *DV/DD, so different differential DVHs can be compared even if their dose bin sizes are different
- 14.
- 15. Cumulative DVH • Volumesreceiving at least a given dose value are plotted. • The cumulative DVH integrates the direct histogram, so it always begins at 100% (100% of the organ receives at least 0 dose), and ends at the maximum dose
- 16.
- 19. Problems and Pitfalls 1.DVHs are insensitive to small ‘hot’ and ‘cold’ spots 2. The shape of a DVH alone can be misleading 3. DVHs can only be calculated for defined VOIs 4. DVHs throw away all spatial information
- 20. 1) Insensitiveness tosmall ‘hot’ and ‘cold’ spots Consider comparative DVHs from competing plans • From DVHs, plan 2 appears to be the best …apart from apparently inignificant increase in high dose to posterior fossa • Posterior fossa
- 22. 2) The shapeof a DVH alone can be misleading
- 23. 3. DVHs canonly be calculated for defined VOIs.
- 24. 4. DVHs throwaway all spatial information
- 25. Visual assessment ofdose distributions • The most direct and informative representation of a treatment plan available - however…. • 3-D dose distributions are large and cumbersome and difficult to analyse quantitatively • User interactivity is essential to extract the most information from dose distributions (slice selection/multi slice display, dose banding, dose querying etc).
- 26. • Provide asuccinct and quantitative method of representing 3-d dose within selected VOI’s -however… • DVH’s should only be used in conjunction with careful visual analysis of 3-d dose distributions • In particular, care should be taken when analysing large volumes using DVH’s • DVH’s should always be assessed in conjunction with dose-volume statistics.
- 27. Assessing and rankinga plan—Dose Based Scoring Possible score functions 1.Visual assessment of the 3-d dose distribution 2. Visual assessment of DVHs 3. Quantitative analysis of dose distributions (conformity index, homogeneity index etc) 4. Quantitative analysis of DVHs (max, min, dose-to-volume etc)
- 28.