PROGRESS TOWARDS AN IMAGE-GUIDED
STEREOTACTIC SMALL ANIMAL IRRADIATOR
Stereotactic Irradiation of Small Animals
Essential Irradiator Characteristics
• High dose rate (up to 10 Gy/min)
Pidikiti R, Stojadinovic S, Saha D, Speiser M, Seliounine
S, Song K, Timmerman RD, Solberg TD
Department of Radiation Oncology
University of Texas Southwestern Medical Center
timothy.solberg@utsouthwestern.edu
• Minimize anesthesia time
• Mimic clinically-applicable dose rates
• Provide uniform tumor dose and minimal peripheral dose
• Multi-directional delivery
• Sharp penumbra
• Variable small field sizes (3 mm to 20 mm)
• Image guidance
• Precise localization
• Visualization of orthotopic tumors / normal structures
Historical Capabilities
Frame
Experience
GammaKnife – coordinate based
Commercial Linac –
visual alignment and image guidance
Dedicated small animal irradiator –
visual alignment and image guidance
1
Linac Experience
Linac Experience
A498Prostate
Renal
C4-2
Cell Cancer
Carcinoma
x 16 45
GyGy
15,322.5,
in 3 fractions
Normalized Tumor Volume versus Time Following Irradiation
10.0
Untreated
5 x 7 Gy
3 x 10 Gy
20 Gy Slow
20 Gy Fast
A549 Lung
Cancer
Normalized Tumor Volume
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
2
4
6
8
10
12
14
16
18
20
22
Days Following First Fraction
Dedicated IGRT Device – Generation One (“The Box”)
SLR
Mirror
Initial Image
Reference DRR
Verification Image
Double Exposure
2
Generation Two
Generation One B – Decouple collimators from
localization device
Ring gantry design with robotic positioning
2D and 3D (CBCT) Image Guidance
Sophisticated Field Shaping
Monte Carlo treatment planning
SU-FF-J-157
Generation One B – Direct digital imaging capabilities
and computer automated localization
Generation One B – Direct digital imaging capabilities
and computer automated localization
Animal support
X-ray Tube
Filter
Collimator
Animal support
Varian PaxScan 1313
Digital Imager
Positioning stages
Digital panel
Positioning stage
3
Generation One B – add
horizontal rotation stage
Beam Characteristics
Percent Depth Dose (250 kVp)
SSD 25 cm
100
10 mm Diameter
90
P D D (% )
Lookup
Table
Dynamic positioning
during treatment
5 mm Diameter
80
7.5 mm Diameter
70
3.5 mm Diameter
1 mm Diameter
60
50
40
30
20
10
0
0
20
40
60
80
100
120
140
Depth (mm)
Correlation with Monte Carlo
Beam Characteristics
Dose Rate versus Field Size (250 kVp)
20 cm SSD
4
Off Axis Ratios
Penumbra (mm)
Transverse - axis
Penumbra (mm)
Perpendicular - axis
1.0 mm Collimator
0.79
0.91
3.5 mm Collimator
0.71
1.05
5.0 mm Collimator
0.73
1.10
7.5 mm collimator
0.6
1.16
10.0 mm Collimator
0.75
1.33
Nominal Aperture Diameter
15 Gy
Orthotopic Glioma Model
Orthotopic Lung Tumor in Mice
Pre-Tx
1 wk
2 wk
Initial Position
Irradiate
30 Gy
Localize and Verify
Pre-Tx
1 wk
2 wk
5
08-28-08
09-09-08
09-23-08
10-06-08
10-13-08
10-17-08
20 Gy
Orthotopic Lung Tumor in Rats
Irradiation on 8-28-08
10 Gy
08-28-08
09-09-08
09-23-08
10-01-08
x
Orthotopic Prostate Tumor Model
Orthotopic Prostate
Tumor Model
Micro CT Plan
Micro MR Plan
6
Orthotopic Prostate Tumor Model
Pre-localization
A
Summary
Post-localization
B
We are developing a number of tumor and normal tissue
models to explore biology of large dose per fraction irradiation
New devices are needed to properly mimic stereotactic delivery
in humans in small animal models
AP
C
D
Lat
Thank you
7