Hanson Ian M, Hansen Vibeke N, Olaciregui-Ruiz Igor, van Herk Marcel
Joint Department of Physics, The Royal Marsden NHS Foundation Trust and The Institute of Cancer Research, Sutton, UK.
Phys Med Biol. 2014 Oct 7;59(19):N171-9. doi: 10.1088/0031-9155/59/19/N171. Epub 2014 Sep 11.
Using an Electronic Portal Imaging Device (EPID) to perform in-vivo dosimetry is one of the most effective and efficient methods of verifying the safe delivery of complex radiotherapy treatments. Previous work has detailed the development of an EPID based in-vivo dosimetry system that was subsequently used to replace pre-treatment dose verification of IMRT and VMAT plans. Here we show that this system can be readily implemented on a commercial megavoltage imaging platform without modification to EPID hardware and without impacting standard imaging procedures. The accuracy and practicality of the EPID in-vivo dosimetry system was confirmed through a comparison with traditional TLD in-vivo measurements performed on five prostate patients.The commissioning time required for the EPID in-vivo dosimetry system was initially prohibitive at approximately 10 h per linac. Here we present a method of calculating linac specific EPID dosimetry correction factors that allow a single energy specific commissioning model to be applied to EPID data from multiple linacs. Using this method reduced the required per linac commissioning time to approximately 30 min.The validity of this commissioning method has been tested by analysing in-vivo dosimetry results of 1220 patients acquired on seven linacs over a period of 5 years. The average deviation between EPID based isocentre dose and expected isocentre dose for these patients was (-0.7 ± 3.2)%.EPID based in-vivo dosimetry is now the primary in-vivo dosimetry tool used at our centre and has replaced nearly all pre-treatment dose verification of IMRT treatments.
使用电子射野影像装置（EPID）进行体内剂量测定是验证复杂放射治疗安全实施的最有效方法之一。先前的工作详细介绍了基于EPID的体内剂量测定系统的开发，该系统随后被用于取代调强放疗（IMRT）和容积调强弧形放疗（VMAT）计划的治疗前剂量验证。在此，我们表明该系统可在商业兆伏级成像平台上轻松实现，无需对EPID硬件进行修改，也不会影响标准成像程序。通过与对五名前列腺癌患者进行的传统热释光剂量计（TLD）体内测量结果进行比较，证实了EPID体内剂量测定系统的准确性和实用性。EPID体内剂量测定系统最初所需的调试时间约为每台直线加速器10小时，令人望而却步。在此，我们提出了一种计算直线加速器特定EPID剂量测定校正因子的方法，该方法允许将单一能量特定的调试模型应用于来自多个直线加速器的EPID数据。使用该方法可将每台直线加速器所需的调试时间减少至约30分钟。通过分析在5年期间在七台直线加速器上获取的1220例患者的体内剂量测定结果，对这种调试方法的有效性进行了测试。这些患者基于EPID的等中心剂量与预期等中心剂量之间的平均偏差为（-0.7 ± 3.2）%。基于EPID的体内剂量测定现已成为我们中心使用的主要体内剂量测定工具，几乎取代了所有IMRT治疗的治疗前剂量验证。
