背景:在放射治疗中越来越多地使用复杂和高剂量率的治疗方法,需要先进的探测器来提供准确的剂量测定。而不是仅仅依靠预处理质量保证(QA)测量,许多国家现在要求使用体内剂量测定法,由此在治疗期间将剂量计放置在患者的表面上。理想情况下,体内探测器应该是灵活的,以符合患者的不规则表面。
目的:本研究旨在表征一种新型氢化非晶硅(a-Si:H)辐射探测器,用于治疗性X射线束的剂量测定。检测器是柔性的,因为它们直接制造在柔性聚酰亚胺(Kapton)衬底上。
方法:通过结合剂量学和灵活性研究,研究了该技术作为实时柔性检测器的应用潜力。获得了基本剂量测定量的测量值,包括输出因子(OF),剂量率依赖性(DPP),能源依赖,百分比深度剂量(PDD),和角度依赖。本研究中研究的a-Si:H检测器的响应直接针对当前用于QA实践的市售电离室和固态二极管进行基准测试。
结果:a-Si:H检测器在直接检测kV和MV治疗X射线时表现出显着的剂量线性,校准灵敏度范围为(0.580±0.002)pC/cGy至(19.36±0.10)pC/cGy,作为探测器厚度的函数,area,和应用偏差。关于剂量测定,a-Si:H检测器准确地获得了与市售检测器溶液平行的测量结果。PDD响应与通过Geant4模拟预测的预期轮廓紧密匹配,PTWFarmer电离室和PTWROOS室。PDD性能的最显著变化为5.67%,在3毫米的深度观察到的探测器无偏操作。有了外部偏见,对于水当量塑料中的所有深度(表面至250mm),PDD响应与参考数据的差异限制在±2.92%.在0°和180°角度的照射之间显示非常小的角度依赖性,最显著的变化是在110°相对入射角下收集的电荷减少7.71%。还报告了能量依赖性和每脉冲剂量依赖性,结果与文献一致。最值得注意的是,a-Si:H检测器的灵活性被量化为样品弯曲到7.98mm的曲率半径,其中记录的光敏度在平坦时降低了初始器件响应的(-4.9±0.6)%。必须提及的是,在体内患者剂量测定期间,这种小的弯曲半径是不可能的。在更现实的场景中,弯曲半径为15-20毫米,检测器响应的变化保持在±4%内。大幅弯曲后,当探测器恢复到平坦状态时,其光敏性为原始响应的(99.1±0.5)%。
结论:这项工作成功地表征了一种基于沉积在Kapton基板上的薄膜a-Si:H的柔性检测器,用于治疗性X射线剂量测定。探测器表现出与市售剂量计平行的剂量测定性能,同时也表现出优异的灵活性结果。
BACKGROUND: The increasing use of complex and high dose-rate treatments in radiation therapy necessitates advanced detectors to provide accurate dosimetry. Rather than relying on pre-treatment quality assurance (QA) measurements alone, many countries are now mandating the use of in vivo dosimetry, whereby a dosimeter is placed on the surface of the patient during treatment. Ideally, in vivo detectors should be flexible to conform to a patient\'s irregular surfaces.
OBJECTIVE: This study aims to characterize a novel hydrogenated amorphous silicon (a-Si:H) radiation detector for the dosimetry of therapeutic x-ray beams. The detectors are flexible as they are fabricated directly on a flexible polyimide (Kapton) substrate.
METHODS: The potential of this technology for application as a real-time flexible detector is investigated through a combined dosimetric and flexibility study. Measurements of fundamental dosimetric quantities were obtained including output factor (OF), dose rate dependence (DPP), energy dependence, percentage depth dose (PDD), and angular dependence. The response of the a-Si:H detectors investigated in this study are benchmarked directly against commercially available ionization chambers and solid-state diodes currently employed for QA practices.
RESULTS: The a-Si:H detectors exhibit remarkable dose linearities in the direct detection of kV and MV therapeutic x-rays, with calibrated sensitivities ranging from (0.580 ± 0.002) pC/cGy to (19.36 ± 0.10) pC/cGy as a function of detector thickness, area, and applied bias. Regarding dosimetry, the a-Si:H detectors accurately obtained OF measurements that parallel commercially available detector solutions. The PDD response closely matched the expected profile as predicted via Geant4 simulations, a PTW Farmer ionization chamber and a PTW ROOS chamber. The most significant variation in the PDD performance was 5.67%, observed at a depth of 3 mm for detectors operated unbiased. With an external bias, the discrepancy in PDD response from reference data was confined to ± 2.92% for all depths (surface to 250 mm) in water-equivalent plastic. Very little angular dependence is displayed between irradiations at angles of 0° and 180°, with the most significant variation being a 7.71% decrease in collected charge at a 110° relative angle of incidence. Energy dependence and dose per pulse dependence are also reported, with results in agreement with the literature. Most notably, the flexibility of a-Si:H detectors was quantified for sample bending up to a radius of curvature of 7.98 mm, where the recorded photosensitivity degraded by (-4.9 ± 0.6)% of the initial device response when flat. It is essential to mention that this small bending radius is unlikely during in vivo patient dosimetry. In a more realistic scenario, with a bending radius of 15-20 mm, the variation in detector response remained within ± 4%. After substantial bending, the detector\'s photosensitivity when returned to a flat condition was (99.1 ± 0.5)% of the original response.
CONCLUSIONS: This work successfully characterizes a flexible detector based on thin-film a-Si:H deposited on a Kapton substrate for applications in therapeutic x-ray dosimetry. The detectors exhibit dosimetric performances that parallel commercially available dosimeters, while also demonstrating excellent flexibility results.