Using a 3D printer for 2D beam profile measurements in proton radiotherapy.

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.