Real-time telerobotic 3D ultrasound
for soft-tissue guidance
concurrent with beam delivery
Dimitre Hristov, Radiation Oncology, Stanford University
AAPM 55th Annual Meeting,
August 4-8, Indianapolis,
Indiana
The team
 Stanford Radiation Oncology
 Can Kirmizibayrak
• Stanford Bio-robotics
– Ken Salisbury
– Jeff Schlosser
 Philips Ultrasound
Investigations
 Vijay Shamdasani
 Steven Metz
Research supported by Stanford Bio-X, Philips
Ultrasound, and NIH STTR Grant to SoniTrack Systems
Imaging during beam delivery
• Existing add-on solutions are limited:
Radiographic x-ray
Electromagnetic
Add-on, real-time, volumetric, soft-tissue guidance
during radiation beam delivery is unmet challenge
Ultrasound soft-tissue imaging
Prostate
Cervix
Left
Kidney
Liver
Right Lobe
of Liver
Body of
Stomach
Pancreas
Gas
Left Lobe
of Liver
HPV
Challenges with ultrasound guidance
 no intra-fractional guidance capability since an
operator is needed for the image acquisition.
 operator variability in achievable image quality and
utility.
 operator induced organ displacements not present
during the actual beam delivery.
 localization uncertainty from speed of sound variations.
 Select anatomical sites: prostate, liver, breast.
Image guidance architecture
Beam
gating
Linear accelerator
LINAC
Optical
tracker
Accelerator
control console
Anatomy
position
US probe
Patient
US probe
manipulator
US-guidance workstation
computer
High level robot
commands
US image stream
Robot
Control (I7)
control
US imaging
system
US probe position data (6 DOF)
Robotic system enables remote image acquisition
Telerobotic imaging
Remote Haptic Interface
Robot
Schlosser J, Salisbury K, Hristov D, Telerobotic system concept for real-time soft-tissue imaging during
radiotherapy beam delivery, Med Phys. 2010 Dec;37(12):6357-67.
Online internal displacement monitoring
Prostate A/P Trajectory [mm]
2
4
6
8
d
5
threshold
0
trigger signal
10
Rmax Signal
d Signal [mm]
0
10
Prostate M/L Trajectory [mm]
0
1
2
4
R
6
8
10
threshold
0.95
trigger signal
0.9
Tissue Displacement Parameters (TDP):
d - in-plane displacement of correlation peak
R – correlation peak value
Trigger signal is activated if a TDP exceeds action threshold.
J Schlosser, K Salisbury, D Hristov,
Online Image-based Monitoring of Soft-tissue Displacements for Radiation Therapy of the Prostate, IJROBP, 3(5), 08/2012
TDP sensitivity to in-vivo displacements
For TDP thresholds of d=1.4 mm and R=0.963,
and with 95% confidence, in vivo prostate
translations were detected before exceeding
2.3, 2.5, and 2.8 mm in the AP, SI, and ML
directions.
J Schlosser, K Salisbury, D Hristov,
Online Image-based Monitoring of Soft-tissue Displacements for Radiation Therapy of the Prostate, IJROBP, 3(5), 08/2012
From 2D to 4D
2D+time
Bi-plane+time
(X-plane)
X6-1 matrix array
3D+time
(4D)
UIS
2D/3D
IWS
Interventional Workstation
1 GB/s Ethernet
Digital Navigation Link
Probe
position (6 DOF)
11
Image acquisition specifications
2D
3D
“Place and lock” strategy for 3D imaging
Solution: EM brakes + sensing
Electromagnetic
Brakes
Position Encoders
Electromagnetic Brakes
Weight ~13 lbs
Position
Encoders
Workflow related specifications
Planning: CT
Treatment: LINAC
Maintain consistent probe
positioning in planning, treatment
US
probe
Avoid metal in CT field
Solution: plastic wrist + dummy probe
1
2
3
Plastic zone
Large portion of probe
available for operator to
grip by hand
Quick release
probe clip for
easy “dummy”
probe
swapping
Current manipulator version
3D US manipulator
From 2D to 4D: 2nd generation robot
From 2D to 4D: 2nd generation robot
Treatment impact: evaluation tool
Simulation environment incorporating 3D models
of linac, patient, and robot
Probe Position 1: Out of Beam
Probe Position 1: Out of Beam
Probe Position 1: Out of Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
Probe Position 2: Interferes with Beam
US guidance hardware
Treatment beam
LINAC and couch
Probe Position 2: Interferes with Beam
US guidance hardware
Treatment beam
LINAC and couch
Probe Position 2: Interferes with Beam
US guidance hardware
Treatment beam
LINAC and couch
Probe Position 2: Interferes with Beam
US guidance hardware
Treatment beam
LINAC and couch
Probe Position 2: Interferes with Beam
US guidance hardware
Treatment beam
LINAC and couch
Probe Position 2: Interferes with Beam
US guidance hardware
Treatment beam
LINAC and couch
Probe Position 2: Interferes with Beam
US guidance hardware
Treatment beam
LINAC and couch
Probe Position 2: Interferes with Beam
US guidance hardware
Treatment beam
LINAC and couch
Liver SBRT plan comparison
Plan with US guidance hardware
Restricted beam angles
VMAT SBRT
Clinically deployed plan
Unrestricted beam angles
40 Gy Threshold
Liver SBRT plan comparison
Plan with US guidance hardware
Restricted beam angles
VMAT SBRT
Clinically deployed plan
Unrestricted beam angles
20 Gy Threshold
Liver Treatment Plan Comparison
Original Plan (unrestricted beam angles)
Plan w/ US guidance hardware (restricted beam angles)
PTV
GTV
Large Bowel
Portal Vein
Liver
Spine
VMAT SBRT
PTV = Planning Target Volume
GTV = Gross Tumor Volume
Impact on treatment plan
PTV
Rectum
GTV
Bladder
Clinical prostate IMRT plan
Re-optimized IMRT plan with restricted beam angles to avoid US
probe and robot links
Re-optimized plan with 2mm margin reduction as potentially
enabled by real-time image guidance
Plans are nearly identical. Potential margin
reduction from real-time guidance is beneficial.
Conclusions
 Second generation manipulator for tele-robotic
imaging currently under evaluation on volunteers
 Simulation tools are developed to enable
comprehensive study on treatment planning
strategies to account for the manipulator.
 Evaluation of long term effects of radiation on the
transducer performance is still required.
 Cross-validation against other modalities
(radiographic imaging of fiducial markers) is
ultimately necessary.
Questions ?