The radial depth–dose distribution of a ¹⁸⁸W/¹⁸⁸Re β line source measured with novel, ultra-thin TLDs in a PMMA phantom: comparison with Monte Carlo simulations

The radial depth–dose distribution of a prototype ¹⁸⁸W/¹⁸⁸Re β particle line source of known activity has been measured in a PMMA phantom, using a novel, ultra-thin type of LiF:Mg,Cu,P thermoluminescent detector (TLD). The measured radial dose function of this intravascular brachytherapy source agrees well with MCNP4C Monte Carlo simulations, which indicate that ¹⁸⁸Re accounts for ⩾99% of the dose between 1 mm and 5 mm radial distance from the source axis. The TLDs were calibrated using a ⁹⁰Sr/⁹⁰Y β secondary standard. Several correction factors are calculated using analytical and Monte Carlo methods. An analysis of the measurement uncertainty is made. Since it is partly determined by components of uncertainty arising from random effects, repeated measurements yield a lower uncertainty. The expanded uncertainty in the absolute dose at 2 mm radial distance equals 11%, 10%, 9% and 8% for 1, 2, 3 and 5 measurements, respectively. After a correction for source non-uniformity, the measured dose rate per unit source activity at 2 mm radial distance equals (1.53 ± 0.16) Gy min⁻¹ GBq⁻¹ (2σ), in agreement with the value of (1.45 ± 0.01) Gy min⁻¹ GBq⁻¹ (2σ) predicted by the MCNP4C simulations.