3D Evaluation tools Flashcards
What are the 2 FIF approaches?
Adding a new prescription (which adds to the overall dose) - adding the boost
Utilising the same prescription (which does not add to the total/dose) - acting as a contour shield.
What factors affects auto-contour options and why is it beneficial?
image resolution and window levels affect auto-contours.
It minimises the amount of manual editing.
Can be quite accurate
What are the different types of auto-segmentation?
Model based (uses libraries of pre-determined models)
3D Atlas based auto-segmentation (uses user-created datasets instead of models. It outlines relevant structures)
What are the disadvantages of autocontouring tools?
Dependence on image resolution
May require editing
Can be time consuming depending on experience
What is the role of 3D margin generation tools?
Used for making PRV’s.
Is better than manually doing it.
What are the planning criteria?
Target coverage
Normal tissue doses
Plan complexity
Conflict resolution
Safety of delivery
What’s the difference between Absolute mode and Relative mode when displaying isodose lines.
Absolute: 60, 57, 50, etc.
Relative Mode: 100%, 95% , 90%
(can display as either lines or colour wash)
What do we use DVH’s for?
It summarises dose distribution information
We use them to evaluate information.
Show uniformity of dose in a structure
Detect “hotspots” outside the target volume that could cause damage
What are disadvantages of DVH?
All positional information is lost - you don’t know where the high or lose dose regions are.
Hot-spots appear where you least expect them.
Relies heavily on contouring - make sure you check accuracy of your contours
What are DVH metrics?
Quantitative tools such as homogeneity and conformity index.
Define HI index?
is an objective tools to analyse the uniformity of dose distribution in the target volume
What is CI index?
a ratio of the volume receiving the prescribed dose to the PTV.
CI index alone cannot provide any practical information. - Compliance with the treatment plan can only be assessed with visualisation.
