WE‐A‐BRB‐09: Brachytherapy Using Pyroelectric Based X‐Ray Sources
Purpose: To assess the feasibility of a miniature pyroelectric electron and x‐ray sources for brachytherapy applications. Methods: Polarized z‐cut lithium niobate crystals that initially measured 1 cm3 were cut into various thicknesses. Samples were placed individually in a glass chamber held at 1×10‐3 Torr, and heat propagation measurements were taken on opposing z‐axis crystal faces. For electron and x‐ray measurements, crystals were mounted to a 200 micron thick 1 cm2 substrate of high carbon steel. A 35° copper electron wedge target was placed 0.8 cm from the crystal face. The crystal substrate was heated with a Fluxeon Royer‐based induction heater operating at 62 KHz. The liberated electron current was measured using a Keithley 614 electrometer. X‐ray spectroscopy and count rate measurements were made using an Ortec 905‐3 NaI(Tl) detector with an Ortec Trump‐32 MCA and a PC based Geiger‐Muller counter, respectively. Results: Induction heating with a total device current of 212W produced an initial substrate heating of 2.3°C per second from 23°C to 125°C with a maximum tempreture of 149°C in 67 seconds during material testing. Linear heating of the 1 cm thick crystal on the face opposite the substrate was observed (0.182°C/s rise) between 32°C and 68°C over the course of 240 seconds. Heating of 0.33 °C/s was measured during device operation from 22°C to 149°C. Crystals of 1 cm thickness produced x‐ray emissions with a maximum energy of 39 keV. Emission calculations indicate that 7.8×101 1 electrons were produced. This corresponds to an equivalent peak source activity of 0.6 mCi, assuming a 1 % conversion of electrons to X‐ray photons. During the heating period, an emission in packed bursts with a peak current of 4×10‐10A was measured. Conclusions: Pyroelectric based emitters could potentially be used as miniature electron and x‐ray sources for radiation therapy and imaging applications.