The potential of polymer pencil-lead graphite for clinical electron beam dosimetry

Abstract The dosimetric capabilities of tissue equivalent rod-shaped polymer pencil lead graphite (PPLG) has been investigated using an Elekta HD Linac, evaluated for electrons from 6 to 15 MeV and doses in the range 0.5 Gy up to 20 Gy. These encompass the major irradiation value ranges used in electron radiation therapy procedures. Parameters concerning thermoluminescence (TL) dosimetry have been investigated, including reproducibility, TL glow curve, the linearity of dose response, sensitivity, energy response and fading. The smaller diameter PPLG samples (0.3 mm) offer excellent dosimetric characteristics, superior to that of the 0.5 mm, 0.7 mm, and 0.9 mm diameter rods. This study confirms that low-cost Pencil Lead-Graphite (PLG) dosimeters provide energy independent dose sensitive linear response over a wide dose range. The small physical size offers unchallenged point detector spatial resolution, also enjoying minimal rates of fading and insensitivity to room lighting. As such, PPLG offers a viable alternative to current commercial dosimeters, well suited to applications in radiotherapy.