Ghimire Lekhnath, Waller Edward
Faculty of Energy Systems and Nuclear Science, Ontario Tech University, Oshawa, ON, L1G 0C5, Canada.
Health Phys. 2023 Mar 1;124(3):192-199. doi: 10.1097/HP.0000000000001657. Epub 2022 Jan 17.
Dose estimation by electron paramagnetic resonance (EPR) has been accomplished using the standard EPR dosimetry technique (ISO protocol 13304-1 for EPR retrospective dosimetry). However, different studies showed that these techniques have high measurement errors in measuring the low doses (10-100 mGy) in enamel. This work proposes a new method to make a dosimetric signal visible and measurable at low doses. The sample was purified using both chemical and mechanical processes. The pure sample mass and position and the EPR acquisition parameters were optimized to enhance the spectrometer's sensitivity for the quantitative low dose measurements. At the same time to reduce errors from the sample and spectrum anisotropy, the total doses (low plus spike) and the spike dose (4 Gy) were measured by rotating 0 to 360 degrees (i.e., 40 degrees at a time) relative to constant magnetic field direction using a goniometer. Subsequently, the spectra were averaged after their g-factor normalization. However, at low doses (<30 mGy), the radiation induced signal (RIS) was obscured by the background signal (BGS). So, the dose spiking technique was used as an alternative method. Ten low-dose deciduous molar tooth enamel (10-100 mGy) samples were spiked to the higher doses by delivering 4 Gy and measured using the X-band continuous wave (CW) EPR (Bruker EMXmicro) spectrometer. The total dose EPR signal was distinctly visible, and the peak-to-peak (P2P) amplitude height was measured. Then, the total dose was subtracted with the spike, often called a reference sample, to determine the initial low doses. The measurement errors using this method were lower than the previous methods. These results demonstrated that this method could be promising for solving low dose measurement problems in EPR dosimetry with deciduous and permanent tooth enamel.
利用标准电子顺磁共振（EPR）剂量测定技术（EPR回顾性剂量测定的ISO协议13304-1）完成了通过电子顺磁共振（EPR）进行的剂量估算。然而，不同的研究表明，这些技术在测量牙釉质中的低剂量（10-100 mGy）时具有较高的测量误差。这项工作提出了一种新方法，使剂量信号在低剂量下可见且可测量。通过化学和机械过程对样品进行纯化。优化了纯样品的质量、位置以及EPR采集参数，以提高光谱仪对低剂量定量测量的灵敏度。同时，为了减少样品和光谱各向异性带来的误差，使用测角仪相对于恒定磁场方向将总剂量（低剂量加尖峰剂量）和尖峰剂量（4 Gy）旋转0至360度（即每次40度）进行测量。随后，在进行g因子归一化后对光谱进行平均。然而，在低剂量（<30 mGy）时，辐射诱导信号（RIS）被背景信号（BGS）掩盖。因此，使用剂量加峰技术作为替代方法。通过施加4 Gy将10个低剂量乳牙磨牙牙釉质（10-100 mGy）样品加峰至更高剂量，并使用X波段连续波（CW）EPR（布鲁克EMXmicro）光谱仪进行测量。总剂量EPR信号清晰可见，并测量了峰峰值（P2P）幅度高度。然后，用总剂量减去加峰剂量（通常称为参考样品）来确定初始低剂量。使用该方法的测量误差低于先前的方法。这些结果表明，该方法在解决乳牙和恒牙牙釉质EPR剂量测定中的低剂量测量问题方面可能很有前景。
