Proton radiography as a tool for quality control in proton therapy

Abstract

Proton radiography is investigated for its use as a quality control tool in proton therapy. Images were produced both with range and range uncertainty information of protons passing through phantoms (Alderson phantom and a sheep's head). With the range images the correct positioning of the patient with respect to the beam could be verified. The range uncertainty images were used to quantitatively detect range variations of protons passing through inhomogeneities in the patient. These measurements can be used to indicate critical situations during proton therapy or to determine the safety margin around the tumor volume. With the range information the precision of different calibrations of computer tomography Hounsfield values to relative proton stopping power, used for proton treatment planning, was determined. It is found that the precision in range can be improved by a detailed analysis of the calibration data obtained from tissue-substitute measurements, by a factor of 2.5. The resulting range errors are in the order of the positioning precision (approximately 1 mm).