IMRT vs VMAT

Question 1

What is statistical uncertainity?

Answer 1

• % per voxel willing to accept for the final dose calc
• no more then 1.5%
• only in monte carlo

Question 2

What are the levels of fluence smoothing?

Answer 2

• off: creates many segments
• low: creates more segements (used for complex plans)
• med: creates an average no. of segments
• high: creates few segments

Question 3

What is the difference between an objective and constraint?

Answer 3

• objective is an anatomy-sepcific function which establishes dose or biological response goal
• constraint is an anatomy-specific function that must be met

Question 4

What does the conformatily cost function do?

Answer 4

• shape the high dose volume tighlty around the target

Question 5

What is mutlticriteria goals?

Answer 5

• allows OAR to be treated as secondary goal

- trys to achieve better normal tissue sparing if target dose exceeds presription

Question 6

What is a shrink margin?

Answer 6

• enables voxels near the tagrtes and other OAR to have a transition zone between competing cost functions

Question 7

What is constained optimisation?

Answer 7

• all nomal tissue objectives met at risk of not meeting target objectives

Question 8

What is pareto optimisation?

Answer 8

• target dose are met at the risk of not meeting all normal tissue constraint

Question 9

What cost functions are physcial?

Answer 9

• target penalty
• quadratic overdose
• quadratic underdose
• overdose DVH
• underdose DVH
• conformality

Question 10

What cost functions are biological?

Answer 10

• target EUD
• serial
• parallel

Question 11

What is a quadratic overdose?

Answer 11

• used to limit high doses to a structure

Question 12

What is a quadratic underdose?

Answer 12

• used to limit low doses to a structure

- used for targets only

Question 13

What is a target EUD?

Answer 13

• 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

Question 14

What is a serial constraint?

Answer 14

• used to limit dose at the end of a DVH curce but can also apply throughout the whole curve dependent on the k value

Question 15

What is a parallel constraint?

Answer 15

• used to limit dose throughout the middle of the DVH curve

Question 16

What is the root mean sqaured?

Answer 16

• function determining the standard deviation of a sample of voxels that exceed the reference dose

Question 17

What is a maximum dose?

Answer 17

• a hard constraint to limit a maxium dose to a structure

Question 18

What is an overdose DVH?

Answer 18

• acts on a specific point of the DVH defined by the objective dose and maximm volume

Question 19

What does the three levels of k value do?

Answer 19

• 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

Question 20

What are the segmant shape optimisation characteristics?

Answer 20

• optimisation time increases
• plan quality increases
• delivery time decreases
• no. segements decreases
• mu may increase