Biomedical Magnetic Resonance Unit, Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier 73.40, B-1200 Brussels, Belgium.
Med Phys. 2010 Oct;37(10):5448-55. doi: 10.1118/1.3488913.
The experimental determination of doses at proximal distances from radioactive sources is difficult because of the steepness of the dose gradient. The goal of this study was to determine the relative radial dose distribution for a low dose rate 192Ir wire source using electron paramagnetic resonance imaging (EPRI) and to compare the results to those obtained using Gafchromic EBT film dosimetry and Monte Carlo (MC) simulations.
Lithium formate and ammonium formate were chosen as the EPR dosimetric materials and were used to form cylindrical phantoms. The dose distribution of the stable radiation-induced free radicals in the lithium formate and ammonium formate phantoms was assessed by EPRI. EBT films were also inserted inside in ammonium formate phantoms for comparison. MC simulation was performed using the MCNP4C2 software code.
The radical signal in irradiated ammonium formate is contained in a single narrow EPR line, with an EPR peak-to-peak linewidth narrower than that of lithium formate (approximately 0.64 and 1.4 mT, respectively). The spatial resolution of EPR images was enhanced by a factor of 2.3 using ammonium formate compared to lithium formate because its linewidth is about 0.75 mT narrower than that of lithium formate. The EPRI results were consistent to within 1% with those of Gafchromic EBT films and MC simulations at distances from 1.0 to 2.9 mm. The radial dose values obtained by EPRI were about 4% lower at distances from 2.9 to 4.0 mm than those determined by MC simulation and EBT film dosimetry.
Ammonium formate is a suitable material under certain conditions for use in brachytherapy dosimetry using EPRI. In this study, the authors demonstrated that the EPRI technique allows the estimation of the relative radial dose distribution at short distances for a 192Ir wire source.
由于剂量梯度陡峭，从放射性源近距离处测量剂量非常困难。本研究的目的是使用电子顺磁共振成像（EPRI）测定低剂量率 192Ir 丝源的相对径向剂量分布，并将结果与 Gafchromic EBT 胶片剂量测定和蒙特卡罗（MC）模拟的结果进行比较。
选择甲酸锂和甲酸铵作为 EPR 剂量测定材料，并将其用于形成圆柱形体模。通过 EPRI 评估了甲酸锂和甲酸铵体模中稳定辐射诱导自由基的剂量分布。还将 EBT 胶片插入甲酸铵体模中进行比较。使用 MCNP4C2 软件代码进行 MC 模拟。
辐照甲酸铵中的自由基信号包含在单个狭窄的 EPR 线中，EPR 峰峰值线宽比甲酸锂窄（分别约为 0.64 和 1.4 mT）。与甲酸锂相比，使用甲酸铵可将 EPR 图像的空间分辨率提高 2.3 倍，因为其线宽比甲酸锂窄约 0.75 mT。EPRI 结果与 Gafchromic EBT 胶片和 MC 模拟在 1.0 至 2.9 mm 距离内的结果一致，误差在 1%以内。在 2.9 至 4.0 mm 的距离处，EPRI 获得的径向剂量值比 MC 模拟和 EBT 胶片剂量测定低约 4%。
在某些条件下，甲酸铵是一种用于 EPRI 近距离治疗剂量测定的合适材料。在本研究中，作者证明 EPRI 技术可用于估计 192Ir 丝源的短距离相对径向剂量分布。
