Comparison of methods for the measurement of radiation dose distributions in high dose rate (HDR) brachytherapy: Ge-doped optical fiber, EBT3 Gafchromic film, and PRESAGER® radiochromic plastic
Comparison of methods for the measurement of radiation dose distributions in high dose rate (HDR) brachytherapy: Ge-doped optical fiber, EBT3 Gafchromic film, and PRESAGER® radiochromic plastic
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DOI：
10.1118/1.4805100
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发表时间：
2013-06-01
期刊：
影响因子：
3.8
通讯作者：
Nisbet, A.
中科院分区：
文献类型：
--
作者：
Palmer, A. L.;Di Pietro, P.;Nisbet, A.
目的：临床高剂量率(HDR)近距离放射治疗的剂量分布测量因剂量梯度大、剂量变化大、规模小而具有挑战性，但必须验证准确的治疗计划和治疗设备的性能。作者比较和评价了三种可能用于近距离治疗剂量分布测量的剂量测量系统：掺Ge光纤，多道分析的EBT3气致变色薄膜，以及具有光学-CT读数的辐射变色材料PREAGE(R)。方法：对长度为5.0 mm、有源芯为6 mm的Ge掺杂二氧化硅光纤进行敏感分批，并通过常规加热和退火循环测定其热释光性能。使用额定的6 mV直线加速器在三个颜色通道中校准了有效厚度为30微米的EBT3Gf变色薄膜。使用48位透射式扫描仪和先进的多通道分析方法进行剂量测量。用平行光束光学CT扫描仪对直径60 mm、高度100 mm的固体辐射变色聚合物预制体(R)样品进行了分析。每个剂量测量系统都被用来测量作为到Co-60 HDR源径向距离的函数的剂量，并将结果与蒙特卡罗TG-43模型数据进行比较。然后，每个系统被用来测量宫颈近距离放射治疗中沿着一条或多条线的典型临床剂量分布的剂量分布，并将结果与治疗计划系统(TPS)的计算结果进行比较。结果：三种剂量测量系统均能再现孤立源径向剂量函数的总体形状和TPS剂量分布。然而，EBT3的动态范围超过了掺杂光纤和Preage(R)，后两者受到了不可接受的噪声和伪影的影响。在本研究中使用的实验条件下，孤立的HDR源的有效范围为：纤维为5-40 mm，EBT3为3-50 mm，Presage(R)为4-21 mm。纤维在非常低的剂量水平下表现出一些过度响应，在剂量分布测量中受到体积平均效应的影响，在三次重复测量中表现出高达9%的重复性变化。EBT3显示出与蒙特卡罗和TPS剂量分布良好的一致性，三次测量的重复性高达3%。Preage(R)是唯一的真正的3D剂量计，但存在明显的伪影和噪声。结论：研究了3种新出现的剂量学系统在临床近距离治疗剂量分布测量中的比较响应。掺Ge光纤对于单向测量具有很好的空间分辨率，但目前对于复杂的剂量分布评估来说太大了。结合光学CT读数使用PRESAGE(R)在测量真实3D剂量分布方面取得了令人振奋的结果，但还需要进一步的开发工作来降低噪音并改善近距离治疗剂量分布测量的动态范围。多通道分析的EBT3Gafchroic胶片显示了HDR近距离放射治疗中剂量分布的准确和可重复性测量。校准剂量测量在TPS剂量计算的1.5%以内是可能的。EBT3作为2D质量控制或调试工作的剂量计的适用性已得到证明。(C)2013年美国医学物理学家协会。
Purpose: Dose distribution measurement in clinical high dose rate (HDR) brachytherapy is challenging, because of the high dose gradients, large dose variations, and small scale, but it is essential to verify accurate treatment planning and treatment equipment performance. The authors compare and evaluate three dosimetry systems for potential use in brachytherapy dose distribution measurement: Ge-doped optical fibers, EBT3 Gafchromic film with multichannel analysis, and the radiochromic material PRESAGE (R) with optical-CT readout.Methods: Ge-doped SiO2 fibers with 6 mu m active core and 5.0 mm length were sensitivity-batched and their thermoluminescent properties used via conventional heating and annealing cycles. EBT3 Gafchromic film of 30 mu m active thickness was calibrated in three color channels using a nominal 6 MV linear accelerator. A 48-bit transmission scanner and advanced multichannel analysis method were utilized to derive dose measurements. Samples of the solid radiochromic polymer PRESAGE (R), 60 mm diameter and 100 mm height, were analyzed with a parallel beam optical CT scanner. Each dosimetry system was used to measure the dose as a function of radial distance from a Co-60 HDR source, with results compared to Monte Carlo TG-43 model data. Each system was then used to measure the dose distribution along one or more lines through typical clinical dose distributions for cervix brachytherapy, with results compared to treatment planning system (TPS) calculations. Purpose-designed test objects constructed of Solid Water and held within a full-scatter water tank were utilized.Results: All three dosimetry systems reproduced the general shape of the isolated source radial dose function and the TPS dose distribution. However, the dynamic range of EBT3 exceeded those of doped optical fibers and PRESAGE (R), and the latter two suffered from unacceptable noise and artifact. For the experimental conditions used in this study, the useful range from an isolated HDR source was 5-40 mm for fibers, 3-50 mm for EBT3, and 4-21 mm for PRESAGE (R). Fibers demonstrated some over-response at very low dose levels, suffered from volume averaging effects in the dose distribution measurement, and exhibited up to 9% repeatability variation over three repeated measurements. EBT3 demonstrated excellent agreement with Monte Carlo and TPS dose distributions, with up to 3% repeatability over three measurements. PRESAGE (R) gave promising results, being the only true 3D dosimeter, but artifacts and noise were apparent.Conclusions: The comparative response of three emerging dosimetry systems for clinical brachytherapy dose distribution measurement has been investigated. Ge-doped optical fibers have excellent spatial resolution for single-direction measurement but are currently too large for complex dose distribution assessment. The use of PRESAGE (R) with optical-CT readout gave promising results in the measurement of true 3D dose distributions but further development work is required to reduce noise and improve dynamic range for brachytherapy dose distribution measurements. EBT3 Gafchromic film with multichannel analysis demonstrated accurate and reproducible measurement of dose distributions in HDR brachytherapy. Calibrated dose measurements were possible with agreement within 1.5% of TPS dose calculations. The suitability of EBT3 as a dosimeter for 2D quality control or commissioning work has been demonstrated. (c) 2013 American Association of Physicists in Medicine.