The Spectral Measurement of Scattered Radiation From a Clinical Linear Accelerator Using a CZT Detector

The study of the induced radioactivity following radiotherapy with high energy X-rays from medical linear accelerator. Patient equivalent phantom made of Polymethyl methacrylate (PMMA) of 30x30x27 cm size irradiated with 15 MV X-rays from Versa HD medical linear accelerator form Elekta. Induced radioactive and ambient dose rates were measured at 0.25, 0.5 and 1 m from beam center using GR1® spectrometry with Cadmium Zinc Telluride (CZT) detectors having energy resolution less than 2%. Spectrum analysis was performed using MultiSpect software. The measured spectrum showed 511 keV annihilation photons possibly as a result of positron emitter of which most likely candidates are 62 Cu(T1/2: 9.7 min), 64 Cu (T1/2: 12.7 h )  and 57 Ni  (T1/2:  35.6 h) and a  peak at ≈ 1780 keV that could be attributed 28 Al and 214 Bi radioisotope. Ambient photon dose rates post radiotherapy treatment ranged 660 µGyh -1 at o.5 m to 41 µGyh -1 at 1 m. These values agree well with the results presented in the literature. Keywords: Radiotherapy; Activation Products; Gamma spectrometry; Occupational exposure; Medical Linear Accelerator. DOI: 10.7176/ALST/83-05 Publication date: November 30 th 2020