DVH

Question 1

Why plan evaluation?

Answer 1

In order to critically evaluate what is planned. To create the best/most accurate plan

Question 2

Advantages of DVHs

Answer 2

• The dose to an entire volumetric structure is reduced to a single graph
  
  • Demonstrate the dose that various organs receive
  • Highlight “hot and cold” areas within a structure.
• DVHs from competing treatment plans can be displayed on one report for comparison.

Question 3

Limitations of DVH

Answer 3

• DVHs obscure information about the precise geometric position of dose within an organ

Too much information may be provided and it becomes difficult to assess the overall clinical effect of the dose distribution

Question 4

How DVHs have altered the way in which we view treatment planning compared to 2-D plan evaluation

Answer 4

2D uses:
	- Isodose distribution 
	- Max / Min / Mean values (ICRU 50) 
	- Dose profiles 
Integral dose
It is useless for other slices

DVH uses volume vs absolute/relative dose to compare dose distribution throughout organs

Question 5

How reliable are DVHs as a plan evaluation tool?

Answer 5

Assists but should be used in conjunction with traffic light system (score card) as it does not provide actual location of hot/cool areas

Question 6

Dose Profiles

Answer 6

graphs of dose versus distance from the central ray, at fixed depths

Question 7

Cumulative DVH

Answer 7

DVH is a plot of the volume of the anatomical structure receiving a certain dose
Considered more useful and commonly used

Question 8

Differential DVH

Answer 8

This DVH is a plot of volume of the organ receiving a dose within a specified dose interval

Question 9

What are the 2 types of DVH

Answer 9

Differential and cumulative

Question 10

Requirements for DVH calculation

Answer 10

• A structure must be contoured to be available for DVH
  
  • Anatomical structures must be contoured onto multiple cross sections
  • dose must be calculated volumetrically
    prescribed dose must be defined

Question 11

DVH accuracy depends on

Answer 11

• Resolution of the dose grid, e.g. 0.25, 0.40
  • CT scan volume, vol for parallel/serial organs
  • Dose calculation algorithm, Adaptive convolve vs CC Convolution vs Monte
  Carlo
  • Accuracy of the ROI contouring- important to contour structures in different
  colours for visualisation

Question 12

QUANTEC

Answer 12

Provides a summary of the dose/volume/ outcome for many organs
Determines acceptable dose/volume constraints

Question 13

Hot areas

Answer 13

The concave curve represents a structure in which most of the structure receives a low dose, but with small areas of high dose
Tail area
Aim for it to be in PTV
Problematic if it is outside the PTV