Prompt gamma-ray imaging with a nuclear emulsion for in vivo dose verification in proton therapy

We propose a new concept of single photon emission computed tomography (SPECT) system using nuclear emulsion technique to detect prompt gamma-rays for in vivo three-dimensional dose verification in proton therapy. It is capable of being dead-time-free at clinical dose rates, neutron-background-free and of high three-dimensional resolution. A first prototype emulsion gamma camera was tested at Nagoya Proton Therapy Center. The gamma camera which measures 62.5 × 50 × 3.2 mm
³
(0.28 radiation length) was put on the sidewall of the phantom. A water phantom was irradiated with 200 MeV proton beams using a spot scanning nozzle at clinical dose rates. Our developed emulsion gamma camera confirmed its potential as a detector for emulsion SPECT system for in vivo dose verification in proton beam radiotherapy.