AbstractID: 8186 Title: Low Dose Megavoltage CT Cone Beam Reconstruction for Patient
Alignment
This work is to demonstrate that 3D Mega-voltage CT (MVCT) cone beam reconstruction can be performed with a
small patient dose and can be correlated with the planning CT for patient alignment purposes. An amorphous silicon
flat panel electronic portal imaging device was used for image acquisition. The 41 x 41 cm2 active detector area was
located 133 cm from the source. The Primus linac parameters were adjusted to allow the delivery of a small fraction
of a Monitor Unit (MU) per image.
The head section of an anthropomorphic phantom (Rando) was placed at isocenter and images were acquired every
two degrees for a complete rotation, for a total of 180 images with less than 15 MU. The 1024 x 1024 pixels images
were rebinned to 512 x 512 images. A filtered back-projection type reconstruction was used to perform a 256 cube
cone beam reconstruction. Fiducial markers were placed on the accessory tray of the linac, and used to correct the
portal images for the lateral movement of the detector.
Despite the very small amount of radiation used for each image (0.08 MU), there is sufficient information to identify
anatomical landmarks. MVCT cone beam reconstruction can be performed with less than 15 MU and provides
visualization of bony anatomy structures adequate for patient positioning verification. Special filters and acquisition
of fewer images per rotation are being investigated as possible ways to increase quality of the images and to further
reduce patient dose. This work is supported by Siemens Medical Solutions.