basics of treatment planning iii...basics of treatment planning iii sastry vedam phd dabr...
TRANSCRIPT
![Page 1: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/1.jpg)
4/1/15
1
Basics of treatment planning III
Sastry Vedam PhD DABR
Introduction to Medical Physics III: Therapy Spring 2015
IMRT and Inverse Planning
![Page 2: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/2.jpg)
4/1/15
2
Compensators
Dynamic Modulation using Jaws in LINAC
![Page 3: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/3.jpg)
4/1/15
3
Static modulation using Jaws
1D
2D
NOMOS MiMIC
![Page 4: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/4.jpg)
4/1/15
4
Linear accelerator
The Multileaf collimator
![Page 5: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/5.jpg)
4/1/15
5
Static (SMLC) IMRT
Dynamic (DMLC) IMRT
! Sum of 1D dynamic deliveries
! Leaves move while radiation is delivered
![Page 6: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/6.jpg)
4/1/15
6
Intensity modulated arc therapy (IMAT)
! In addition to moving the collimators during radiation delivery, gantry also moves
! Minimize leaf movement between gantry locations
! Combination of ! Leaf speed
! Gantry speed
! Dose rate
Interdigitation and tongue and groove effect
! When subfields are joined, tongue and groove artefacts lead to underdosing
! Reduced by factoring in: ! Rotation of
collimator between fields
! Electron transport
! Patient motion
![Page 7: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/7.jpg)
4/1/15
7
Helical tomotherapy
Accuray Cyberknife
![Page 8: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/8.jpg)
4/1/15
8
Physical Basis of IMRT
IMRT basis: The inverse problem
! D – Dose distribution
! b – Vector of individual beam weights
! A – Matric liking each dose-space element to corresponding beam-space element ! Physics of photon tissue interaction ! Can be pre-calculated using simple
equations/Convolution-superposition/Monte Carlo
! Inverse problem ! Given D and A, can we calculate ‘b’?
![Page 9: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/9.jpg)
4/1/15
9
Inverse problem
! Negative beam weights
! Require construction, storage and inversion of too large a matrix A
! It would take too long
! No method to control the behavior of the beam weight vector ‘b’
Degeneracy
! Multiple “solutions” to the inverse problem
! Which solution to accept and which to reject?
! Global and local minima
![Page 10: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/10.jpg)
4/1/15
10
Concept of ‘Cost’
! I – importance of each voxel
! Higher importance to PTV voxels – Tumor conformal planning
! Higher importance to Organs at Risk – Conformal avoidance
Constraints
! Planning constraints
! Physics constraints
! Human constraints
![Page 11: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/11.jpg)
4/1/15
11
Optimization
What we want …
! All types of radiation
! All energies
! All possible number of beams
! All possible number of beam geometries
! All possible fractionation schemes …
What we can want…
! Beams available on a machine
! Number of beams within a reasonable delivery time
! Delivery mechanics
! Time available for treatment planning …
Simulated annealing
! Way to guarantee achievement of local minima
! Instead of rejecting all changes that lead to an increase in the cost function, accept changes with a probability
! T – Temperature
! k – Boltzmann constant
! Set T to be high initially so that a lot of “wrong way” changes are accepted and then reduce T slowly, so that only downhill changes are accepted as iterations progress
! T must be lowered slower than the reciprocal of the logarithm of the iteration number
![Page 12: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/12.jpg)
4/1/15
12
Simulated annealing
Gradient descent
! When the cost function is guaranteed to have no local minima
! Cost function written mathematically and its derivatives exist
! Advantage – Fast
! Disadvantage – Can generate negative beam weights and may require a posteriori adjustment ! Setting negative beam weights to zero
! Addition of constant fluences
! Disturb the optimization
![Page 13: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/13.jpg)
4/1/15
13
Genetic algorithms
! Based on Darwinian theory of evolution
! Categories of solutions proposed via an iterative process
! “Fittest” solutions survive
! Definition of fitness
! Mechanism for evolution
! Bixel intensity values can be considered as chromosomes and are exchanged and/or mutated during the evolution process
Biological optimization
! TCP – Tumor control probability
! NTCP – Normal tissue complication probability
![Page 14: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/14.jpg)
4/1/15
14
Concave and
Convex beams
Clinical IMRT milestones
! First clinical IMRT (excluding wedges/compensators) – NOMOS MIMiC @ Baylor College of Medicine, Houston 1994
! First DMLC treatments – Memorial Sloan Kettering Cancer Center, New York 1996
![Page 15: Basics of treatment planning III...Basics of treatment planning III Sastry Vedam PhD DABR Introduction to Medical Physics III: Therapy Spring 2015 IMRT and Inverse Planning 4/1/15](https://reader033.vdocuments.us/reader033/viewer/2022050610/5fb1cf443afb2c3af92960dc/html5/thumbnails/15.jpg)
4/1/15
15
IMRT delivery techniques