Mini Phantom, with Leveling Platform

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Mini Phantom, with Leveling Platform.

The Mini-Phantom can be used to check the alignment of the internal and external lasers to the radiographic center of CT and PET/CT units and to verify lateral gantry angle.  It can also be used with accelerator units to check vertical and lateral gantry angles, laser alignment and vertical table movement.

The Mini-Phantom is made of clear acrylic measuring 15 cm x 15 cm x 5 cm thick.  One 15 cm x 15 cm side has centering scribe lines that go all the way across the phantom.  All four of the 5 cm x 15cm sides are scribed through the center and two opposite sides are also scribed at 5 cm from center.  The scribe lines are 1.3mm wide and white for ease of viewing the lasers.  All four 5 cm x 15 cm sides have three pinholes, one at center and two at 5 cm from center.  The center pinholes are 1.5 mm dia. to hold a tungsten pin and the other pinholes are 1.0 mm.  Four 1.5 mm dia. tungsten pins are included with the mini-phantom.

The two large holes are 9.5 mm in diameter and are 10.6 cm apart from center to center.  Each hole is in the exact center of a quadrant of the phantom.

Leveling Platform for Mini-Phantom
The Leveling Platform for the Mini-Phantom is made of black acrylic that is 15 cm square x 1.0 cm thick.  A hole in the center of the Mini-Phantom is for a tungsten pin that goes into the Mini-Phantom.  A bubble level and three leveling screws with rubber tips are used to level the platform.  The rubber tips help prevent the platform from moving.

Directions for use in CT or PET/CT
Place the Mini- Phantom on the leveling platform with the pinholes towards the lateral lasers and the 15 cm side with scribe lines towards the foot of the couch.  Align the Mini-Phantom to the center of the couch using the sagittal or overhead lasers.  Level the platform using the bubble level and three leveling screws.  Align the phantom to the CA of the beam by raising or lowering the couch to align the Mini-Phantom with the lateral lasers.  A scan through the center of the Mini-Phantom should show the eight 1mm dia. pinholes and four 1.5mm dia. pinholes.  Verify that the CT lasers are on the center scribe line around the phantom.  Move the couch out so the lateral and ceiling lasers project onto the phantom.  Check the couch movement distance.  Verify that the lateral and ceiling lasers are on the center scribe line on the phantom.  The movement of the lateral or ceiling lasers can also be checked by raising and lowering the lasers to the scribe lines 5 cm from the center.  If present, the sagittal laser should align with the scribe lines on the 15 cm side of the phantom.  The couch vertical movement can also be verified by raising and lowering the couch to the 5cm off- center scribe lines on the phantom.

Directions for use in Accelerators or Conventional Simulators
Insert the four tungsten pins into the four 1.5 mm dia. holes in the Mini-Phantom.  Place the Mini- Phantom on the leveling platform with the pinholes towards the lateral lasers and the 15 cm side with scribe lines towards the foot of the couch.  Align the Mini-Phantom to the center of the couch using the sagittal or overhead lasers.  Level the platform using the bubble level and three leveling screws.  Align the phantom to the CA of the beam by raising or lowering the couch to align the Mini-Phantom with the lateral lasers and by moving the couch in to align with CA crosshairs.  To verify vertical and lateral gantry angles take a radiograph with the gantry in the vertical position and in the lateral position.  The tungsten pins should be on top of each other on the radiographs.  The lateral lasers should align with the center scribe lines and the sagittal laser should align with the scribed line on the 15 cm side of the mini-phantom.  To check the overhead laser, rotate the gantry so the overhead laser shows upon the mini-phantom.  The overhead laser should align with the center scribed line on the top of the mini-phantom.  Raising and lowering the couch to the scribes at 5 cm from center and checking the couch vertical movement indicator can check the couch vertical movement.  To check lateral couch movements rotate the mini-phantom so a side with the scribes 5 cm off-center is facing up towards the gantry.  Then move the couch left and right to align with the scribes that are 5 cm off-center and check the lateral couch movement indicator.