  We have used an inexpensive 3D printer mounting an inexpensive pre-irradiated
silicon diode to measure the 2D dose distribution of a small (approximately
10mm FWHM) proton beam. z was measured with high resolution whereas x was
changed on a 2mm grid for a total of 12 scans and 2 repeats in 20 minutes. The
peak dose to the diode was approximately 530 cGy/s, and no degradation in diode
sensitivity was observed. We present beam profiles and a 2D beam contour
derived from these data.
  Most of the scan time was spent changing x by hand, and a more appropriate 3D
printer along with an improved setup and printer control software would reduce
that to about 1 minute for an end-to-end absolute 2D dose measurement. We
propose extending this to 3D (2D transverse plus depth) for appropriate small
beams by adding a small water tank.
