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 6x 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 500kV. 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 RobotText Box: The 6–axis robot was chosen In order to provide a high degree of freedom in 3D positioning with high precision (± 0.020 mm) of the animal to be irradiated.  It is also a relatively inexpensive solution if compared with quality X-Y-Z precision stages with sufficient range of motion for animal irradiation applications.  The Robot motion (position and speed of movement) is fully programmable and it can also be controlled with a hand-held pendant.  The combination of gantry rotation and positioning capabilities with the Robot will facilitate complex beam delivery and thus provide ample room for dose distribution optimization.
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:

Rotating animal platform using a robotic arm with 6 degrees 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 systemand the X-ray tube from the one computer.

Support:
Arkansas Biomedical Institute and the Arkansas Master Tobacco Settlement fund.
The UAMS Department of Radiation Oncology.
We are grateful for collaboration with Johns Hopkins University.