Determination of Photon Therapy Beam Spectra Using Transmission and Unfolding Techniques

Abstract

For effective radiation therapy, it is crucial to understand the properties of the radiation being utilized. The challenge lies in the dose distribution within an irradiated inhomogeneous medium composed of various tissues, each with different attenuation characteristics. Consequently, it is essential to determine the mass energy absorption coefficient for each point within the irradiated volume and the incident beam spectrum of the therapeutic accelerator to accurately calculate the dose distribution in the treated body area. In this study, our objective was to determine the photon radiation spectrum of a medical linear accelerator using a measurement technique based on the transmission and unfolding method. The radiation spectrum of the Varian DHX therapeutic linear accelerator was analyzed using the attenuation (transmission) method. This study focused exclusively on the 6 MeV photon radiation spectrum. Radiation doses were measured after attenuation through materials such as water, aluminum, lead, iron, and copper. The photon radiation spectrum was determined using these measured data, the known attenuation coefficients for the materials, and the standard unfolding technique, which is well-established in neutron and photon activation measurements. The results of this study demonstrate that the applied technique can reliably provide information about the photon radiation spectrum characteristics of medical linear accelerators. The analysis reveals that the radiation doses calculated using the photon spectrum obtained via the unfolding method are more consistent with the measured values than those calculated using the standard Schiff spectrum.