This document summarizes the integration of an optical tracking system (OTS) for organ motion compensation in scanned ion-beam therapy. The OTS tracks external markers in real-time to monitor and estimate internal organ motion. It has been integrated with the therapy control system to enable lateral beam tracking compensation. Performance studies using breathing phantoms showed sub-millimeter tracking accuracy. Ongoing work aims to improve the motion prediction models and reduce the need for retraining using smaller patient datasets.

1. AAPM 2012 Annual Meeting
Integration of optical tracking for organ motion
compensation in scanned ion-beam therapy
G Fattori[1], N Saito[2], A Pella[1], R Kaderka[2], M Seregni[1], A Constantinescu[2],
P Cerveri[1,3], P Steidl[2], M Riboldi[1,3], G Baroni[1,3] and C Bert[2]
[1] Politecnico di Milano
[2] GSI Helmholtzzentrum für Schwerionenforschung GmbH
[3] Centro Nazionale di Adroterapia Oncologica (CNAO)
31 July 2012

2. Presentation outline
INTRODUCTION: the role of optical tracking system in moving targets treatment
Moving targets treatment in scanned IBT
Optical Tracking Systems (OTS)
SYSTEMS INTEGRATION: integrated setup with GSI Therapy Control System
OTS/TCS integration
RESULTS: performance and dosimetric results
Lateral target motion compensation
Performance study
Preliminary 3D target motion results and future works
2 - 10

3. …
3 - 10
PHASE N
4DCT
TARGET MOTION
PHASE 1
4D
IMAGING
Workflow of moving targets treatment with beam tracking
4D TREATMENT PLAN (TP)
MOTION
DETECTION
X-RAY STEREO PROJECTIONS
SOFT-TISSUE IMAGING
US
MRI
OPTICAL EXTERNAL
SURROGATES TRACKING
ü
ü
ü
²
Non-invasive
High frequency
High accuracy
Surrogate signal
INTERNAL – EXTERNAL
CORRELATION MODELS
ü Periodic imaging
for train/retrain
ü Target position
estimation from
external signal
DOSE
DELIVERY
LATERAL
DEPTH
TREATMENT
VERIFICATION
THERAPY CONTROL SYSTEM (TCS)
OFFLINE PET
IN-BEAM PET

4. Optical Tracking System (OTS)
4 - 10
SMART-DX100, BTS Bioengineering
Windows based workstation
3 free-standing Infrared TVC cameras
15 min calibration procedure
3D reconstruction of markers:
• 3D error < 0.3 mm in 1 m3 volume
• Frequency: 100 Hz
CNAO patient positioning
Ongoing studies on surface reconstruction
OTS APPLICATIONS IN HIGH CONFORMAL RADIATION THERAPY
•
SETUP VERIFICATION: visual feedback during patient daily re-positioning
•
REAL TIME MOTION MONITORING: continuous patient surveillance during treatment

5. Integrated software for setup verification and motion monitoring
IN-ROOM CALIBRATION
5 - 10
SETUP VERIFICATION
PPS
NOMINAL
POSITION
IMAGING
TREATMENT
SETUP
OTS
Room coordinates system
Visually assisted stereotactic
frameless patient positioning
MOTION MONITORING
130
external
Target
Tools for:
§
125
On-line motion phase detection from external surrogates
Amplitude and phase based criteria
Target position estimation with correlation models
State model, Artificial Neural Networks
§
Time prediction for delays compensation
range [mm]
§
120
115
110
Polynomial data fitting: linear, 5 samples
§
Digital TCS communication
UDP socket over Ethernet
105
T*
T
100
111000
112000
113000
114000
115000
116000
time [usec]
117000
118000

6. Software implementation
6 - 10
Optical Tracking System
SHARED RESOURCES!
RCS TRANSFORM
MATRIX
"
LABELLER
PATIENT MODEL
"
FRAMES INTERPOLATION
"
MOTION PHASE
TABLE
"
POLYNOMIAL
"
COEFFICIENTS
"
100 Hz frame rate
TIME CRITICAL THREAD
!
Correction
vector
MOTION PHASE DETECTION
"
[xyz]
Treatment plan
BTU
Steering
magnets
Wedge range
shifter
Lateral
compensation
Depth
compensation
[ MP ]"
CORRELATION MODELS
"
DIGITAL COMMUNICATION (UDP SOCKET)
!
OTS DRIVEN THREAD
!
3D DATA FLOW
Therapy Control System
BREATHING
SIGNAL
"
TARGET
"

7. Lateral target motion compensation by beam tracking
7 - 10
Measurement tools
§ Gafchromic film
§ 5 PTW PinPoint®
chambers
PoliMi breathing phantom
§ Planar motion
§ 18 mm peak to peak
§ Planarity index: median
• 0.038 mm (IQR:0.09)
§ Repeatability: mean ± std
• 0.18 ± 0.3 mm
Prediction
§ 3 samples (30msec)
(visual inspection)
GSI TCS
§ on-the-fly lateral compensation
§ Digital TCS/OTS interface
STATIC
DIRECT
ANN
DELTA % WRT STATIC IRRADIATION
PINPOINT
I
II
III
IV
V
MEDIAN
DIRECT TRACKING
-2.66
-1.09
0.35
-0.61
1.85
-0.61
ANN PREDICTION
2.10
0.61
-5.13
-7.30
-4.63
-4.63
Critical point:
² Residual interplay effect visible on
films due to non optimal systems
communcation/integration

8. OTS processing and communication time measurements
8 - 10
SETUP
OTS
§
16 IR LED ARRAY
§ OTS
3 TVC setup
§ InfraRed LED array
§
16 IR LED λ = 880 nm
§
0.6 usec 10-90% switching time
§ TCS: linux based general purpose workstation
§
TVC 1
TVC 2
“TCS”
UDP
SOCKET
Shared
Memory
TVC 3
NI-6211
4 bit TTL
NI-6211 board; nsec switch time
METHOD
LED ON
UDP receiver
SHM reader
Timestamps delta:
§ UDP receiver Vs LED activation
§ Shared Memory (SHM) reader Vs UDP receiver
RESULTS
2800 measures [usec]
2.5
25
MEDIAN
75
97.5
IQR
DATA transfer
100
Hz
LED vs UDP
10070
12910
16450
19660
257830
6751
100%
UDP vs SHM
76
84
99
161
625.5
77
99.95%
50
Hz
LED vs UDP
10574
15520
20873
25947
44841
10428
100%
UDP vs SHM
27
28
43
49
60
21
100%

9. Ongoing activities: 3D target motion
9 - 10
§ GSI breathing thorax phantom (Steidl et al. 2012)
§ predictors tuning for depth and lateral compensation
§ Correlation model optimization
§ Retrain
§ 1 Gy in cubic volume 35 mm side
§ 20 PTW PinPoint® chambers
MODELS PERFORMANCE: 3D ERROR [mm]
ANN
real
TS points
Modality
Median ± IQR
ANN
4
0.27 ± 0.32
STATE MODEL
214
Retrain
13
0.33 ± 0.23
x coordinate [mm]
212
210
DOSE STUDY [DELTA PERC. WRT STATIC]
Irradiation
204
180000
190000
195000
time [msec]
200000
205000
210000
-0.46 ± 3.31
ANN ESTIMATED
185000
12.23 ± 23.55
DIRECT TRACKING
206
Mean ± Std.Dev
NON COMPENSATED
208
0.6 ± 3.3
STATE MODEL
0.8 ± 3.3

10. Conclusions and future works
10 - 10
ü Demonstrate the feasibility of CNAO OTS integration with GSI scanned ion-beam TCS
ü Demonstrate the experimental use of two breathing phantoms featuring planar (PoliMI)
and 3D (GSI) target motion in beam tracking experiments
ü Demonstrate the functionality of standard digital communication protocol (UDP) for real
time OTS-TCS data stream
ü Describe a method to qualify the OTS processing and data communication time
requirements for time prediction parameters fine tuning
Future works
§
Phantom: clinical breathing pattern from lung patients dataset
§
Treatment verification: in-beam PET
§
Improvements on models: reduced number of retrain with smaller dataset

11. Thank you
11 - 10
These activities were partially founded by the EU-FP7 ULICE
project, WP 4: “Ion-therapy for intra-fractionally moving targets”.
Grant agreement number 228436