Explicit estimation of out-of-field neutron and gamma dose equivalents during proton therapy using thermoluminescence-dosimeters

Proton therapy is capable of delivering the planned dose more conformally to the tumour volume, reducing the dose to surrounding healthy tissue in comparison to conventional photon radiotherapy. However, secondary fast neutrons and gamma rays are produced due to the interaction of the primary proton beam with the beam shaping and modifying devices inside the beam delivery nozzle as well as the patient themselves, resulting in an unwanted radiation exposure to sensitive organs located outside the treatment volume. At the Westdeutsches Protonentherapiezentrum Essen (WPE) we have explicitly estimated the neutron and gamma dose equivalents at the outer surfaces of a 26 x 26 x 32 cm(3) polystyrene plate phantom irradiated with a 226 MeV scanned proton pencil beam using commercially available alpha-Al2O3:C (TLD-500) and 7LiF:Ti, Mg (TLD-700) dosimeter pairs. The scanned volume in the phantom and the delivered proton dose were 1 L (10 x 10 x 10 cm(3)) and 10.3 Gy respectively. This small neutron and gamma dosimeter, based on existing TLD technology, will be implemented for in vivo out-of-field dosimetry for patients receiving proton radiotherapy at WPE in the near future. (C) 2011 Elsevier Ltd. All rights reserved.