L 20: IMRT Flashcards
(31 cards)
IMRT
- VMAT plans have faster delivery time than IMRT
- IMRT dose rate to any point is time dependent
QA for IMRT
90-95% of diodes meeting the 3% criteria are acceptable
Multi-segmented static field delivery
Step and shoot
- Multiple fields
- Each field is sub divided into sub fields
Dynamic Delivery
Sliding window
Leaf chasing
Opposing leads sweep same time and unidirectionally each with a different velocity as a function of time.
MLCs Doimetric Check
QA can be 1mm offset
1.7% mid leaf transmission
2..7% between leafs tongue and groove pattern
Mechanical Tests
- Leaf acceleration and deceleration
- Position of accuracy of leaves
- Routine mechanical checks, precision 0.2mm
- Stability of leaf speed/Dose profile across adjacent leaves
IMRT treatment planning
Validation of phantom in the treatment planning system as well as validation of the dose delivered to the phantom
VMAT Plan Advantages
- Decrease the chance of intrafractional motion.
- ability to use 360 deg beam directions
- Variable dose rate
- Variable ganry speed
- Faster treatment time
- Uses fewer MUs than static gantry, so less treatment time and less chance of motion
- Does not require FFF plans
DIrect aperture optimization
- MLC shaped aperatures and beam weights are optimized directly
Segmental Multileaf IMRT
SMLC
Step and shoot method
stop and shoot method
MLC s move between segments while the beam is off
Beam lets
The division of a beam into an array of small beams from beams eye view, whic allows for generation of an intensity map to assist in the planning of IMRT
IMRT arc therapy
Uses dynamic MLCs which move when the beam is on and while the gantry rotates
Local minimun
- Cost function is higher than global minimum
- Stochastic algorithm
Global minimum
Cost of a plan is at an absolute min value
Lowest cost function , meeting all objectives
Conventional treatment planning
Uses
* Beam aperatures
* Beam modifiers
* Relative beam weights
IMRT
Inverse planning
Uses
* Desirable dose distribution
IMAT
Intensity modulated arc therapy
Conformal arc using MLC
Gantry rotates
Beam on during rotation
Dynamic MLCs
That shape around target
leaf sequencing algorithm IMRT planning for segmental multileaf IMRT
Produces static MLCconfigurations and calculates MU per each configuration
Helical Tomotherapy
- TYpe of IMRT
- Moving through a doughnut CT scanner
- Couch moves contin
IMRT Intensity map
Open density matrix
Fluence map
- It is a set of intensity values of IMRT Beamlets
- Each beamlet is 0.5 x 0.5 cm or 1cm x 1cm
- It is a 2D representation of the intensity of the beam
IMAT, 2 arcs in same plane
- We rotate the collimator for one of the arcs
- To avoid additive accumulation of the interleaf leakage in the axial planes
Pareto Curve
Pareto Surface
X Axis: Normal tissue cost
Y Axis: Target cost
* Increasing the targe coverage will result in a cost to the nrmal tissue objective
Multi criteria IMRT optimization
Generates a multitude of plans allowing the planner to visualize trade offs between plan coverage and organs at risk with a graphical user interface
Dynamic MLC
DMLC
Leaf speed accuracy is important
