Characterisation of graphite-based material for dosimetry in the mammographic energy range

Abstract

Present work explores the use of carbon-based materials as novel material for in-vivo radiation dosimetry during routine screening mammography, in part to reliably predict the average glandular dose (AGD) imparted to the patient. The study herein proposes the use of highly uniform 0.3 mm of 2B and HB grade polymer pencil-lead graphite (PPLG) i.e. approximately 95 wt % and 61 wt % graphite content, respectively and also using graphite produced commercially in the form of 50 μm thick sheets, addressing variation in lattice structure and defects resulting from low x-ray doses. Comparison was made with highly-oriented pyrolytic graphite (HOPG), a pure ordered synthetic form of graphite. Due to their small size and distinctive shape, these samples can be placed on the body surface in the field of view during the examination without compromising the mammogram reading. Investigations of thermo- and photoluminescence dose dependence, as well as changes in Raman spectroscopic features, have been conducted with a focus on the relationship between absorbed radiation energy and induced material changes within the dose range 3–11 mGy. The influences, are readily understood to relate to defect density, structural alterations and radiation-driven thermal annealing, all irradiation alterations occurring at the microscopic level. Within the doses study, all graphite samples demonstrated excellent linear response in respect of thermoluminescence yield per unit mass. In terms of sensitivity, 2B samples outperformed HB, graphite sheet (GS), and HOPG. In mammographic studies graphite sheets show particular promise as a probe of skin dose, with negligible prospect for interference with the breast image an individual patient during routine screening, closely matching the effective atomic number of soft tissues, additionally providing the basis of a low-cost yet highly effective system for studies of radiation-driven changes in carbon.