IMRT vs VMAT Flashcards
What is statistical uncertainity?
- % per voxel willing to accept for the final dose calc
- no more then 1.5%
- only in monte carlo
What are the levels of fluence smoothing?
- off: creates many segments
- low: creates more segements (used for complex plans)
- med: creates an average no. of segments
- high: creates few segments
What is the difference between an objective and constraint?
- objective is an anatomy-sepcific function which establishes dose or biological response goal
- constraint is an anatomy-specific function that must be met
What does the conformatily cost function do?
- shape the high dose volume tighlty around the target
What is mutlticriteria goals?
- allows OAR to be treated as secondary goal
- trys to achieve better normal tissue sparing if target dose exceeds presription
What is a shrink margin?
- enables voxels near the tagrtes and other OAR to have a transition zone between competing cost functions
What is constained optimisation?
- all nomal tissue objectives met at risk of not meeting target objectives
What is pareto optimisation?
- target dose are met at the risk of not meeting all normal tissue constraint
What cost functions are physcial?
- target penalty
- quadratic overdose
- quadratic underdose
- overdose DVH
- underdose DVH
- conformality
What cost functions are biological?
- target EUD
- serial
- parallel
What is a quadratic overdose?
- used to limit high doses to a structure
What is a quadratic underdose?
- used to limit low doses to a structure
- used for targets only
What is a target EUD?
- used to prescribe dose to targets
- rationalises that intense hot spots are fine to offset under dosing to prescribe a equivalent dose to which is prescibed
What is a serial constraint?
- used to limit dose at the end of a DVH curce but can also apply throughout the whole curve dependent on the k value
What is a parallel constraint?
- used to limit dose throughout the middle of the DVH curve
What is the root mean sqaured?
- function determining the standard deviation of a sample of voxels that exceed the reference dose
What is a maximum dose?
- a hard constraint to limit a maxium dose to a structure
What is an overdose DVH?
- acts on a specific point of the DVH defined by the objective dose and maximm volume
What does the three levels of k value do?
- small: assumes a large volume efect (low and high dose volumes are evenly weighted)
- large: assumes thereis less tolerance for large high dose volume
- k=1 is equivalent to setting a mean dose constraint
What are the segmant shape optimisation characteristics?
- optimisation time increases
- plan quality increases
- delivery time decreases
- no. segements decreases
- mu may increase
