AbstractID: 6925 Title: Kilovision: Kilovoltage Imaging Using a Medical Linear Accelerator
We are examining the potential of integrating a kilovoltage x-ray source inside the head
of a medical linear accelerator. Such a source could be used to image bony anatomy and
fiducial markers, or to form CT images. We have studied the thermal and thermalmechanical properties of a megavoltage target assembly modified to include a kilovoltage
target and the electron transport of kilovoltage electrons inside the head of a megavoltage
linear accelerator. The thermal analysis uses a finite element analysis program called
ANSYS 5.6 and the electron optics calculations use a program called CPO. The thermal
model includes forced convection, fully developed boiling, and critical heat flux heat
transfer. The electron optics calculations include the effects of space charge on electron
transport. The residual magnetic fields along the electron path were measured in a
decommissioned linear accelerator and used as input into the electron optics calculations.
For a 1200W thermal load (120kVp, 10mA) and a 2x2mm2 source, the wall temperature
of the cooling tubes exceeds boiling temperature and nucleate boiling occurs. To
overcome this limitation, the target angle has to be reduced, an extra cooling tube has to
be added and the target has to be changed to a 0.2mm W-Re plate. The solenoid magnet
rather than the bending magnet generates the largest residual magnetic fields. Substantial
magnet shielding is required for good focussing of the electron beam to occur. Overall,
installation of a kilovoltage x-ray source in the head of an accelerator is practical from
thermal and electron optics considerations