SACRTD

Small Animal Conformal Radiation Therapy Device

We are developing a Small Animal Conformal Radiation Therapy Device (SACTRD)
that will provide a degree of geometric/anatomic targeting comparable to
what is achievable in current clinical radiotherapy practice to promote
translational research in radiation oncology and radiation sciences. The
SACRTD will integrate 3D-conformal radiation therapy delivery with Cone Beam
Computerized Tomography (CBCT) imaging for registration, localization, tumor
and normal tissue segmentation, 3D dose computation/optimization and
advanced treatment planning tools.

  Highlights:

-  On-board CBCT imaging, 0.5mm voxel

-  Adequate dose output, ~ 200 cGy/min

-  Dose localization to < 1 mm

-  Setup/repositioning  ~ 0.5 mm 

-  Advanced treatment planning tools,

             -  Dose
calculation and verification

 Shielding
and Safety:

 The X-ray tube has
two foci, a small focus of 0.4 mm, 640 W, which can be coupled with a
collimating cone for irradiation field sizes ≤ 4 mm x 4 mm, and a large
focus of 3.0 mm, 3000 W, which for field sizes of up to 60 mm x 60 mm with
appropriate collimators. The maximum dose rate at 1 meter from the tube is ~
13 Sv/hr at maximum tube voltage and maximum anode dissipation, and produces
< 10 mSv/hr of leakage radiation.

 The system is housed in a 6
x 6 x 6 ft³ enclosure constructed out of a steel frame and lead
blankets.  The X-ray source is mounted ~40 inch from the floor. The
door-on-a-wheel has a magnetic lock with an emergency switch to open from
inside for safety.  A door interlock (contact switch) ensures that no
beam-on is possible when door is open. The structure holding the X-ray tube
and other components is constructed from modular framing system (80/20 Inc).
The shielding of SACRTD meets/exceeds the
safety requirements of NCRP Report 49, which is good for sources up to 500
kV. The primary beam is shielded by 1 inch of lead equivalent or more and
secondary and leakage radiations are shielded by ½ in of lead equivalent
(two layers of 10 lb/ft² lead blankets)            

Focused/Collimated X-Ray
Beam Delivery System With Robotic Positioning:

Adept
Viper 6-Axis Robot
Cone Beam
CT System with Robotic Positioning of Animal:

 The cone beam CT
image will be acquired with a digital X-ray imager using the same X-ray tube
used for therapy but operated at a lower energy (~ 80-120 kVp). The animal,
posit­ioned at isocenter, will be rotated by the robot. Robot motion, X-ray
activation and data acquisition by the imager will be under
computer-control. Planar radiographic projections of an animal image are
recorded by the digital X-ray imager aSi flat panel detector. These 2D
proj­ections will be processed to reconstruct a 3D volumetric image.

Key
features:

-
Stationary beam/detector

-
Rotating animal platform using a robotic arm with 6 degree of
freedom.

-
Imager: aSi Flat panel digital X-ray detector

-
80-120 kVp, dose ~5 cGy

Collimators
for Conformal Radiation Delivery:

 Current
efforts (2008) are focused, dosimetric characterization of the
X-ray beam at various energies, installation and implementation of the
imaging system and software, development of a treatment planning platform,
and controlling of the robotic animal positioning system, the imaging system
and the X-ray tube from the one computer.

SUPPORT:

Arkansas Biomedical Institute and the Arkansas Master Tobacco Settlement
fund.

The Central Arkansas Radiation Therapy Institute (CARTI).

The UAMS
Department of Radiation Oncology.

Collaboration:

We are grateful
for collaboration with John Hopkins University.