在诊断能量范围内的 OSLD 的特征。

Characteristics of an OSLD in the diagnostic energy range.

机构信息

Department of Radiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, USA.

出版信息

Med Phys. 2011 Jul;38(7):4396-405. doi: 10.1118/1.3602456.

DOI:10.1118/1.3602456

PMID:21859040

Abstract

PURPOSE

Optically stimulated luminescence (OSL) dosimetry has been recently introduced in radiation therapy as a potential alternative to the thermoluminescent dosimeter (TLD) system. The aim of this study was to investigate the feasibility of using OSL point dosimeters in the energy range used in diagnostic imaging.

METHODS

NanoDot OSL dosimeters (OSLDs) were used in this study, which started with testing the homogeneity of a new packet of nanoDots. Reproducibility and the effect of optical treatment (bleaching) were then examined, followed by an investigation of the effect of accumulated dose on the OSLD indicated doses. OSLD linearity, angular dependence, and energy dependence were also studied. Furthermore, comparison with LiF:Mg,Ti TLD chips using standard CT dose phantoms at 80 and 120 kVp settings was performed.

RESULTS

Batch homogeneity showed a coefficient of variation of <5%. Single-irradiation measurements with bleaching after each OSL readout was found to be associated with a 3.3% reproducibility (one standard deviation measured with a 8 mGy test dose), and no systematic change in OSLDs sensitivity could be noted from measurement to measurement. In contrast, the multiple-irradiation readout without bleaching in between measurements was found to be associated with an uncertainty (using a 6 mGy test dose) that systematically increased with accumulated dose, reaching 42% at 82 mGy. Good linearity was shown by nanoDots under general x-ray, CT, and mammography units with an R2 > 0.99. The angular dependence test showed a drop of approximately 70% in the OSLD response at 90 degrees in mammography (25 kVp). With the general radiography unit, the maximum drop was 40% at 80 kVp and 20% at 120 kVp, and it was only 10% with CT at both 80 and 120 kVp. The energy dependence study showed a range of ion chamber-to-OSLDs ratios between 0.81 and 1.56, at the energies investigated (29-62 keV). A paired t-test for comparing the OSLDs and TLDs showed no significant variation (p > 0.1).

CONCLUSIONS

OSLDs exhibited good batch homogeneity (<5%) and reproducibility (3.3%), as well as a linear response. In addition, they showed no statistically significant difference with TLDs in CT measurements (p > 0.1). However, high uncertainty (42%) in the dose estimate was found as a result of relatively high accumulated dose. Furthermore, nanoDots showed high angular dependence (up to 70%) in low kVp techniques. Energy dependence of about 60% was found, and correction factors were suggested for the range of energies investigated. Therefore, if angular and energy dependences are taken into consideration and the uncertainty associated with accumulated dose is avoided, OSLDs (nanoDots) can be suitable for use as point dosimeters in diagnostic settings.

摘要

目的

光激励发光（OSL）剂量测定法最近已被引入放射治疗中，作为热发光剂量计（TLD）系统的潜在替代品。本研究的目的是研究在诊断成像中使用的能量范围内使用 OSL 点剂量计的可行性。

方法

本研究使用了 NanoDot OSL 剂量计（OSLD），首先测试了一包新的 NanoDot 的均匀性。然后检查了重现性和光学处理（漂白）的效果，接着研究了累积剂量对 OSLD 指示剂量的影响。还研究了 OSLD 的线性度、角度依赖性和能量依赖性。此外，还使用标准 CT 剂量体模在 80 和 120 kVp 设定下与 LiF:Mg，Ti TLD 芯片进行了比较。

结果

批次均匀性显示变异系数<5%。单次照射测量，每次 OSL 读数后进行漂白，发现重现性为 3.3%（用 8 mGy 测试剂量测量的一个标准差），并且从一次测量到另一次测量，OSLD 的灵敏度没有系统变化。相比之下，在测量之间不进行漂白的多次照射读数与不确定性（使用 6 mGy 测试剂量）相关，该不确定性随着累积剂量的增加而系统增加，在 82 mGy 时达到 42%。NanoDot 在普通 X 射线、CT 和乳房 X 光摄影设备下显示出良好的线性度，R2>0.99。角度依赖性测试显示在乳房 X 光摄影（25 kVp）中 OSLD 响应下降约 70%。在普通 X 光摄影设备中，最大下降幅度为 80 kVp 时为 40%，120 kVp 时为 20%，而在 CT 中均为 10%，在 80 和 120 kVp 时均为 10%。能量依赖性研究表明，在所研究的能量（29-62 keV）范围内，电离室与 OSLD 之间的比值在 0.81 至 1.56 之间。对 OSLD 和 TLD 进行配对 t 检验显示无统计学差异（p>0.1）。

结论

OSLD 表现出良好的批次均匀性（<5%）和重现性（3.3%）以及线性响应。此外，在 CT 测量中，它们与 TLD 没有统计学上的显著差异（p>0.1）。然而，由于累积剂量较高，在剂量估计中发现了较高的不确定性（42%）。此外，NanoDot 在低 kVp 技术中显示出较高的角度依赖性（高达 70%）。发现能量依赖性约为 60%，并为所研究的能量范围建议了校正因子。因此，如果考虑到角度和能量依赖性，并避免与累积剂量相关的不确定性，OSLD（NanoDot）可以作为诊断设置中的点剂量计使用。