Treatment Planning for CyberKnife®
Radiosurgery
Matthew Witten, PhD, DABR
Director, Division of CyberKnife Radiosurgery
Winthrop-University Hospital
Mineola, New York
I have received honoraria from
Accuray, Inc.
Winthrop-University Hospital
CyberKnife Center
Chronology and Statistics
Acceptance and beam commissioning – August –
September 2005.
First patient treated October 2005.
To date: 1,123 patients treated and 4,543 fractions
delivered.
Patient Stats
Fractions Delivered
Distribution of Sites Treated
Intracranial vs. Extracranial Treatments
CyberKnife Treatment Delivery
CyberKnife Treatment Planning
CyberKnife Treatment Delivery
CyberKnife® Robotic Radiosurgery System
Delivering radiosurgery anywhere in the body with sub-millimeter
accuracy
Continual image guidance throughout the treatment
Automatically tracks, detects, and corrects for
tumor and patient movement
Applications:
Intracranial – frameless
Spinal – unlimited reach
Body – lung, pancreas, liver, prostate, etc.
Unhindered robotic mobility
Treat virtually any tumor from any direction
CyberKnife® Robotic Radiosurgery System
Intracranial & Spinal Applications
Proven sub-millimeter targeting accuracy
Frameless intracranial treatments made possible with continual
image guidance throughout the treatment
Enables practical multiple fractionation
Diverse applications made possible with flexible
robotic mobility
Unlimited intracranial access – including
extreme peripheral intracranial tumors
Unlimited spinal access – from cervical to sacral
CyberKnife® Robotic Radiosurgery System
Extracranial Applications
Proven sub-millimeter targeting accuracy
Applications anywhere in the body
No stereotactic frames / Minimal immobilization
More efficient patient setup
Dynamically moves beams to follow respiratory
motion in real-time
Maximizes healthy tissue sparing
†
Completely non-invasive / fiducial-less for spine and lung
Reduces time-to-treatment, related procedure risks, and cost of
treatment
† Limited to tumors of specific size and location
TARGETING SYSTEM
X-ray sources
Manipulator
Synchrony®
camera
Treatment
Couch
Linear
accelerator
ROBOTIC DELIVERY
SYSTEM
Image
detectors
System Overview
System Overview: Linear Accelerator
•
600 MU/min X-band Linear Accelerator
– Average Cranial Treatment Time: 20-30 minutes*
– Average Extracranial Treatment Time: 30-55 minutes*
* Based on simulations
System Overview: Image Guidance System
•
Continual imaging throughout the treatment with integrated patient
and tumor movement corrections
• Automatically track, detect, and correct
•
Fixed / rigid ceiling imaging sources
– High kV image resolution
•
Flush-mounted, in-floor x-ray image detectors
Targeting Accuracy
CyberKnife® System Accuracy
Stationary Tumors
CyberKnife delivers treatments with sub-mm accuracy*
Site
1
2
3
4
5
6
7
8
9
Mean
SD
anterior
-0.32
-0.24
0.00
-0.46
0.35
-0.04
-0.55
-0.18
-0.15
left
0.26
-0.26
0.04
-0.33
0.32
-0.14
-0.72
-0.86
0.31
superior
0.21
-0.17
0.08
-0.38
0.60
-0.14
-0.01
-0.24
0.11
radial
0.46
0.39
0.09
0.68
0.76
0.20
0.91
0.91
0.36
0.530.53
mm
0.30
±0.3 mm
CyberKnife Total Targeting Error in mm for systems tested 2003-2004.
*References: Yu C, Main W, Taylor D, Kuduvalli G, Wang M, Apuzzo M, Adler J. An Anthropomorphic Phantom Study of the
Accuracy of CyberKnife Spinal Radiosurgery. Neurosurgery, November 2004.
CyberKnife® System Accuracy
Moving Tumors
Dieterich, S, et al. The CyberKnife Synchrony™ Respiratory Tracking
System: Evaluation of Systematic Targeting Uncertainty
Objective: Quantify systematic geometric uncertainties in treatment
delivery using Synchrony for range of simulated respiratory motions
Methodology: Accuracy measured at Georgetown University Hospital,
Boulder Community Hospital, UCSF
Site 1
Site 2
Site 3
Mean
SD
0 deg
1.05
0.62
0.46
0.71
0.31
15 deg
1.05
0.74
0.11
0.63
0.48
30 deg
1.08
0.55
0.64
0.76
0.28
Results: Mean systematic error of 0.70 ± 0.33 mm
Synchrony accuracy specification: 1.5 mm
Reference: Dieterich S, Taylor D, Chuang C, Wong K, Tang J, Kilby W, Main W. The CyberKnife Synchrony Respiratory Tracking
System: Evaluation of Systematic Targeting Uncertainty
E2E Test – Targeting Accuracy
Synchrony® Respiratory Tracking System
Optical markers on the surface of the patient
Markers monitored in real time by the Synchrony camera system
Xsight™ Spine Tracking
System
How it Works…
DRR (from CT)
Image A
Image B
Live kV image
Displacement Field
Skeletal Structure Tracking
81 Corresponding
Points can be identified
Point of Interest
DRR Image
Corresponding Point
Live Image
CyberKnife Treatment Planning
MultiPlan™ Treatment Planning
Optimized for intracranial and
extracranial radiosurgery
Advanced, automated and
manual image fusion
Automated planning and
contouring tools
Goals of Radiosurgical Treatment Planning
High conformality.
Steep dose gradients around the target volume.
Sparing of adjacent organs at risk (OARs).
Reasonable treatment times.
Collimators
12 fixed collimators – 5 mm to 60 mm in diameter.
Iris variable collimator – tungsten blades shape apertures
5 mm to 60 mm in diameter.
Path Sets
Beams delivered from fixed points in space called nodes.
Nodes arranged in spherical (intracranial applications) or
ellipsoidal (extracranial applications) configurations.
Nominal SAD is 800 mm for intracranial treatments, 9001000 mm for extracranial treatments, and 650 mm for
trigeminal treatments.
Treatment Planning Steps
Selection of Imaging Center
CM of fiducials or user-selected for other tracking modes.
Contouring
Collimator Selection
Balance conformality and treatment time.
Usually use multiple collimators to achieve this compromise.
Beam Targeting
Points randomly generated within and near the boundary of the
targeted VOI on the central axes of the beams in the beam set.
Dosimetric Optimization / Beam and MU Reduction
Optimize the dose distribution based on user-defined constraints.
Set max and min MU constraints (earlier than MP v 3.0) or
perform beam reduction (MP v 3.0 and later) and MU
optimization.
Simplex Optimization
Sequential Multi-Criteria Optimization
Strategies for Treatment Planning
Fixed number of constraint points in the grid, so set tight
limits around structures.
Use shell structures to tune the isodose lines.
Inner shell at a small distance ( 5mm to 10 mm ) from target
volume to constrain higher isodose lines.
Outer shell at a larger distance (greater than 10 mm) from target
to constrain lower isodose lines.
Use a shell thickness of 1 - 2 mm.
Use additional isolated manual constraint points to finetune the dose distribution when the shell structures are
insufficient.
Meningioma
Spine
Trigeminal
Prostate
Liver Met
Lung
Challenges with MultiPlan
No user feedback during dosimetric optimization.
No explicit inclusion of points on the boundaries of VOIs
for DVH calculation.
Constraints are all hard constraints.
Versions of MP without SMCO can yield no result at the
conclusion of dosimetric optimization if no feasible
solution exists.
No DVH constraints.
Proposed New Approach
Research conducted independently of Winthrop-University
Hospital, with collaborator Owen Clancey.
Use a population-based approach to find a global minimum of
the fitness function.
DVH constraints.
Intelligent point sampling, with points on the boundaries of VOIs explicitly
included.
Local minima induced by DVH constraints easily overcome.
Carefully designed population operators provide superior
calculation speeds and rates of convergence.
Algorithm is very forgiving of non-ideal choice of constraint
weights.
No hard constraints except for MU boundedness constraints.
Given the dimensionality of the problem and topology of the
fitness function, trajectory methods are probably inferior to
population-based methods of optimization.