Infrastructure for IGRT
[bits, bytes, and but(t)s]
Bruce Curran
University of Michigan
Ann Arbor, MI
Disclosures
• My department has research affiliations
with
– Varian Medical Systems
– Calypso
What is “Infrastructure”?
… most generally, is the set of interconnected
structural elements that provide the framework for
supporting the entire structure. It usually applies
only to structures that are artificial. The term is
used differently in a variety of fields; perhaps the
single most well-known usage is in economics,
where it refers to physical infrastructure such as
buildings and roads.
From http://en.wikipedia.org/wiki/Infrastructure
Infrastructure
The notion that a structure has an in-ternal
fra-mework is popular especially in business
organizations where a dependency on
interconnected information technology
systems has become as prevalent as a city's
dependency on interconnected conveyance
systems for power, people and things.
From http://en.wikipedia.org/wiki/Infrastructure
What’s in an “Infrastructure”?
• Computer Systems
– Storage
– Visualization
– Analysis Tools
•
•
•
•
Networking / Connectivity
People Resources
Machine Resources
Training
State of IGRT
• Weekly Portal / Orthogonal Imaging
– Bony Anatomy Alignment / Review
– Marker Alignment / Review
• Daily Portal / Orthogonal Imaging
• Weekly Cone-Beam CT
– Soft Tissue Alignment
• Daily Cone-Beam CT
• Other Imaging / Positioning Modalities
–
–
–
–
US
Infrared
Video
RF, Other positioning signals
Sample Intra-Fraction
Prostate Movement
AP
IS
LR
Position (cm)
0.0
-0.2
-0.4
0
60
120
180
240
0
60
120
180
240
300
360
420
480
540
600
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
300 360 420 480 540 600
Time (s) Courtesy of James Balter
Impact of prostate positioning strategies
(Litzenberg RSNA 2005)
PTV Margin (mm)
12
10
IS
AP
LR
8
6
4
2
0
Skin Marks
Initial
skin-based
setup
Initial
Setup to
prostate
Pre-Beam
Correction
Intrabeam
correction
Our Model Department
• Treats 40 patients / day / linac
– (10,000 treatments / year)
• 3 linear accelerators
• One CT Simulator
• We’ll ignore for the moment
– Brachytherapy
– Multimodality Imaging Studies
Computer Systems: Storage
• Initial Imaging
– CT Study (150 images) = 75 MB*
• Inhale/exhale/free breathing imaging
– 150 Images x 3 = 225 MB
• 4DCT
– 300 Images x 10 bins = 1,500 MB
*Note: Our CT department currently averages 500 slices per CT exam
Computer Systems: Storage
• So, for our hypothetical Clinic
– 70% have a single imaging study
– 20% have an inhale/exhale study
– 10% have a 4DCT study
Leads to 99,000 MB / year / linac
or 297 GB / year
Computer Systems: Storage
• Portal Images (weekly imaging)
– ~512 x 512 x 2 bytes = 0.5 Mbytes/image
– 4-8 images on first day of treatment
– Weekly orthogonal Imaging
– And the answer is
2,800 – 3,600 MB / year / linac
8.4 – 10.8 GB / year
Computer Systems: Storage
• Portal Images (daily imaging)
– ~512 x 512 x 2 bytes = 0.5 Mbytes/image
– 4-8 images on first day of treatment
– Daily orthogonal Imaging
– And the answer is
10,800 – 11,600 MB / year / linac
32.4 – 34.8 GB / year
– More realistically, 30% are daily imaged
5,215 – 6,000 MB / year / linac
15.63 – 18.0 GB / year
Computer Systems: Storage
• Cone-Beam CT Imaging (weekly)
– ~512 x 512 x 2 bytes = 0.5 Mbytes/image
– Image Volume 512 x 512 x ?? =
• 55 slices = 27.5 MB
• 256 slices = 128 MB
– Image 20% of patients =
11,000 - 51,200 MB / linac / year
33.0 - 153.6 GB / year
Computer Systems: Storage
• Cone-Beam CT Imaging (daily)
– ~512 x 512 x 2 bytes = 0.5 Mbytes/image
– Image Volume 512 x 512 x ?? =
• 55 slices = 27.5 MB
• 256 slices = 128 MB
– Image 10% of patients =
27,500 - 128,000 MB / linac / year
82.5 – 384.0 GB / year
Computer Systems: Storage
• Summary:
– 50% (weekly orthogs):
– 30% (daily orthogs):
– 10% (weekly CBCT):
– 10% (daily CBCT):
• Total Verification (per linac):
• Imaging (per linac):
• GRAND TOTAL (clinic):
1.60 GB
3.36 GB
15.00 GB
75.00 GB
94.0 GB
99.0 GB
579.0 GB
– x 3 for backup / RAID: 1.737 TB/year
But …..
• Where do we store this information?
– CT Simulator Archive
– Planning System
– Treatment Management System
– ...
So you may end up with 3 or 4 times the original
information depending upon your practice, and
you may not be able to archive it per year (some
systems will not allow archiving of partial data), and
we haven’t talked about saving the CBCT projections
for research or other investigations (estimates from
Sonke were about 10x the CBCT size!)
And …
• Currently Radiology at UM is averaging a
50%/year growth in imaging information
(total exams are relatively flat)
• As we learn more about how to use IGRT
to reduce PTV margins, we will most
certainly increase the number of advanced
(e.g. 4D or CBCT) scans we utilize in
planning and treatment
But …
• We will likely have some deformation
maps for our inhale/exhale and 4DCT data
In the worst case, these could be {x,y,z}
vectors, one per pixel, so
LEAVE SOME EXTRA ROOM!!!!!!!!!
Visualization
• What tools will we need to efficiently align
patients while under treatment
– Match and Adjust
– 2D – 2D matching
– 3D – 3D matching
– Registration / Fusion
• Proper CRT/LCD and lighting at linac
console
Match and Adjust
Match and Adjust
• Works with markers, bony anatomy
• Can require experienced RTT for accurate
use
• Filtering may be required to highlight
anatomy (diaphragm)
• Needs someone to indicate the
appropriate anatomy for matching
2D-2D Match
2D – 2D Match
• Using kV imaging, gives higher contrast
images
– Allows true lateral imaging for markers in
pelvis
• Reduces RTT skill necessary for accurate
match
• Still limited to high contrast objects
3D – 3D Match
3D – 3D Match
• Allows soft tissue matching, e.g. GTV
• Can generally reduce errors to those of
ITV
• Tools, time often not yet quite there
– Additional time / training
Networking / Connectivity
• How long are you willing to wait?
– Server throughput
– Network speed
– Workstation speed
• Some Recommendations
– 1 GB network connectivity at server
• Additional network cards in a busy department
– Fast Disk Systems
• 10,000 RPM SCSI or SATA
– Pentium 4 or equivalent
• As much speed, particularly on I/O bus, as you can afford
Networking / Connectivity
• Dataset Transfer Time
– 100 MB Image Dataset = ~ 1 Gbit of dat
– Using an 100 Mbit ethernet
•
•
•
•
10 Seconds?
Overhead of about 20%
Typical efficiency of about 30%
Result is about 30 – 40 s
BUT ….
Networking / Connectivity
• Network efficiency drops rapidly as
network traffic increases
– At 60% utilization, efficiency may be as low as
10% (collisions due to network algorithms)
– Delay becomes highly unpredictable
– Thus the 30 – 40 s may actually end up as 3 4 minutes or more
• Routers / firewalls add additional latency
People Resources
• Off-line Analysis
– Need for additional RTTs/dosimetrists
• On-line Analysis
– Who approves the move? When?
(Reimbursement is muddying these waters!)
• MD Resources
– More images / anatomy to review
• Physics Resources
– QA / Analysis / Protocol Development
• IT Support
Machine Resources
• TIME!!!!!
Training
• Team Approach
– Develop procedures and modify as needed!
• Typically train 1-4 RTTs for initial
implementation
– QA runs are useful for procedure familiarity
• Documentation / References
Linac
4DTC
1
Mode Up OBI
Setup Field
OBI WS
2
Click 2D/2D Match
5
Analyze
3
Send Field and
Choose Technique
Press Motion Enable
Foot Switch to
Acquire
Manual
Matching
Review new couch
Positions
4
Send Next Field and
Choose Technique
Press Motion Enable
verify
6
Save couch
position for
current session
or all sessions.
Send in first
field
Foot Switch to
Acquire
Send couch
position and
treat or verify
with imaging
treat
Press Motion Enable
Beam On
Courtesy of Scott Hadley
Acknowledgement
Control Systems
• Paul Keall said it all!!!!!
Discussion