Soares Christopher, Drupieski Chris, Wingert Brian, Pritchett Garey, Pagonis Vasilis, O'Brien Michelle, Sliski Alan, Bilski Pawel, Olko Pawel
National Institute of Standards and Technology, Gaithersburg, MD, USA.
Radiat Prot Dosimetry. 2006;120(1-4):78-82. doi: 10.1093/rpd/nci622. Epub 2006 May 30.
Absorbed dose rate measurements of a 50 kV(p) handheld X-ray probe source in a water phantom are described. The X-ray generator is capable of currents of up to 40 microA, and is designed for cranial brachytherapy and intraoperative applications with applicators. The measurements were performed in a computer-controlled water phantom in which both the source and the detectors are mounted. Two different LiF thermoluminescence dosemeter (TLD) phosphors were employed for the measurements, MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P). Two small ionisation chambers (0.02 and 0.0053 cm(3)) were also employed. The TLDs and chambers were positioned in watertight mounts made of water-equivalent plastic. The chambers were calibrated in terms of air-kerma rate, and conventional protocols were used to convert the measurements to absorbed dose rate. The TLDs were calibrated at National Institute of Standards and Technology (NIST) in terms of absorbed dose rate using a (60)Co teletherapy beam and narrow-spectrum X-ray beams. For the latter, absorbed dose was inferred from air-kerma rate using calculated air-kerma-to-dose conversion factors. The reference points of the various detectors were taken as the center of the TLD volumes and the entrance windows of the ionisation chambers. Measurements were made at distances of 3-45 mm from the detector reference point to the source center. In addition, energy dependence of response measurements of the TLDs used was made using NIST reference narrow spectrum X-ray beams. Measurement results showed reasonable agreement in absorbed dose rate determined from the energy dependence corrected TLD readings and from the ionisation chambers. Volume averaging effects of the TLDs at very close distances to the source were also evident.
本文描述了在水模体中对50 kV（p）手持式X射线探头源的吸收剂量率测量。该X射线发生器能够产生高达40微安的电流，专为颅内近距离治疗和使用施源器的术中应用而设计。测量在计算机控制的水模体中进行，源和探测器均安装在该水模体中。测量采用了两种不同的LiF热释光剂量计（TLD）磷光体，即MTS-N（LiF:Mg,Ti）和MCP-N（LiF:Mg,Cu,P）。还使用了两个小电离室（0.02和0.0053 cm³）。TLD和电离室放置在由水等效塑料制成的防水支架中。电离室根据空气比释动能率进行校准，并使用传统协议将测量结果转换为吸收剂量率。TLD在美国国家标准与技术研究院（NIST）使用⁶⁰Co远距离治疗束和窄谱X射线束根据吸收剂量率进行校准。对于后者，使用计算出的空气比释动能-剂量转换因子从空气比释动能率推断吸收剂量。各种探测器的参考点取为TLD体积的中心和电离室的入射窗。在从探测器参考点到源中心的距离为3 - 45毫米处进行测量。此外，使用NIST参考窄谱X射线束对所用TLD的响应测量的能量依赖性进行了测量。测量结果表明，从能量依赖性校正的TLD读数和电离室确定的吸收剂量率具有合理的一致性。在非常靠近源的距离处，TLD的体积平均效应也很明显。
