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 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:

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.