Construction of a radiation beam scanner and investigation of volume averaging correction factor effects on beam-profile.

In radiation beam-profile measurements, an accurate positioning of the detector with high position resolution is essential. For this purpose, we built a scanning device capable of moving a detector in three dimensions (3D) using mainly parts from a commercial 3D-printer. The accuracy and repeatability of movement was tested with caliper, laser displacement sensor and repeated 60Co beam-profile measurements in a water phantom. The results from the caliper and the sensor showed position accuracy for the scanner to be better than $\pm$150 μm. The standard deviation of the error in position from laser sensor measurements was approximately 30 μm, and the beam profile scans showed a maximum deviation from the mean position of 50 μm. The effect of volume averaging correction factors on 60Co beam-profile was investigated with two different sized ionization chambers. The differences in the profiles were reduced significantly after applying the correction factors.