SU-D-BRCD-02: A Novel Cylindrical 3D Water Scanner for Beam Data Collection: I. Validation of the Automatic-Setup

To determine the accuracy and reproducibility of the automatic- setup procedure of a 3D water scanner (3D SCANNER, Sun Nuclear Corp). The procedure automatically aligns the scanner's coordinate system to the Linac coordinate system. A unique off-center detector holder extends the scan range to 630 mm, eliminating the need for scanner shifts for large-field scans.

The automatic-setup procedure provides means to automatically (1) level the tank; (2) zero the detector position to water surface; (3) align the scanner's coordinate system to the Linac system; and (4) correct motor hysteresis. After automatic-setup, (1) and (2) were evaluated visually by three physicists. Step (3) was tested by moving one of the jaws to the isocenter and scans were made along the jaw edge. Angular misalignment between the scanner and the Linac would Result in a noticeably tilted profile. Step (4) was tested by scanning with the chamber moving forward and then backward five times. The accuracy of the off-center detector holder was tested by comparing scans made using the regularand the off-center detector holders. All tests were repeated three times.

All tests of the water surface and horizontal chamber movementwere acceptable from the nine independent evaluations. Scans along the jawedge resulted in < 1% in profile tilt, corresponding to < 0.05 degree in angular misalignment. Same direction scans resulted in field edge differences < 0.05 mm, and < 0.2 mm when compared to scans in thereverse direction. There was no difference in accuracy when different scan speeds were used. Profiles obtained using the regular and the off-centerdetector holders were identical.

The automatic-setupprocedure resulted in accurate alignment of the 3D SCANNER to the Linac. These results were user-independent. It also provides the ability to scan large fields without the need to change tank setup. This work was partially supported by a research grant from Sun Nuclear Corp., Melbourne, FL.