Pinhole Camera Measurements of Prompt Gamma-rays for Detection of Beam Range Variation in Proton Therapy

Abstract

We have designed and constructed a pinhole camera system to monitor variations in the beam range during the course of proton beam therapy. The camera consists of a shielding enclosure made of lead plates with a pinhole aperture and a CsI(Tl) scintillation detector. The design of the camera was performed using a Monte Carlo program to optimize the shielding structure. The proton energy was assumed to be 50 MeV for empirical verification by using a proton beam and a water phantom at the proton-beam facility of the Korea Cancer Center Hospital. The enclosure thickness was determined so as to reduce the background radiation well below the prompt gamma distribution through the pinhole aperture. The aperture was shaped and located to view the endpoint of the proton range. Experimental results showed that the gamma distribution was sensitive to variations in the proton beam range of the order of 1 mm in water.