Hemdal Bengt, Herrnsdorf Lars, Andersson Ingvar, Bengtsson Gert, Heddson Boel, Olsson Magnus
Department of Medical Radiation Physics, Lund University, Malmö University Hospital, SE-205 02 Malmö, Sweden.
Radiat Prot Dosimetry. 2005;114(1-3):436-43. doi: 10.1093/rpd/nch556.
The Sectra MicroDose Mammography system is based on direct photon counting (with a solid-state detector), and a substantially lower dose to the breast than when using conventional systems can be expected. In this work absorbed dose measurements have been performed for the first unit used in routine mammography screening (at the Hospital of Helsingborg, Sweden). Two European protocols on dosimetry in mammography have been followed. Measurement of half value layer (HVL) cannot be performed as prescribed, but this study has demonstrated that non-invasive measurements of HVL can be performed accurately with a sensitive and well collimated solid-state detector with simultaneous correction for the energy dependence. The average glandular dose for a 50 mm standard breast with 50% glandularity, simulated by 45 mm polymethylmethacrylate, was found to be 0.21 and 0.28 mGy in March and December 2004, respectively. These values are much lower than for any other mammography system on the market today. It has to be stressed that the measurements were made using the current clinical settings and that no systematic optimisation of the relationship between absorbed dose and diagnostic image quality has been performed within the present study. In order to further increase the accuracy of absorbed dose measurements for this unit, the existing dose protocols should be revised to account also for the tungsten/aluminium anode/filter combination, the multi-slit pre-collimator device and the occurrence of a dose profile in the scanning direction.
Sectra微剂量乳腺摄影系统基于直接光子计数（采用固态探测器），与使用传统系统相比，预计对乳房的剂量要低得多。在这项工作中，对用于常规乳腺摄影筛查的第一台设备（位于瑞典赫尔辛堡医院）进行了吸收剂量测量。遵循了两项欧洲乳腺摄影剂量测定协议。虽然无法按规定进行半价层（HVL）测量，但本研究表明，使用灵敏且准直良好的固态探测器，同时对能量依赖性进行校正，可以准确地进行HVL的非侵入性测量。由45毫米聚甲基丙烯酸甲酯模拟的、腺体组织占50%的50毫米标准乳房，其平均腺体剂量在2004年3月和12月分别为0.21和0.28毫戈瑞。这些值远低于当今市场上的任何其他乳腺摄影系统。必须强调的是，这些测量是在当前临床设置下进行的，并且在本研究中尚未对吸收剂量与诊断图像质量之间的关系进行系统优化。为了进一步提高该设备吸收剂量测量的准确性，应修订现有的剂量协议，以考虑钨/铝阳极/滤过器组合、多狭缝预准直器装置以及扫描方向上剂量分布的情况。
