Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, USA.
Department of Physics and Astronomy, University of Victoria, Victoria, BC, Canada.
Med Phys. 2020 Apr;47(4):2013-2022. doi: 10.1002/mp.14049. Epub 2020 Feb 19.
Image-guided small animal irradiators (IGSAI) are increasingly being adopted in radiation biology research. These animal irradiators, designed to deliver radiation with submillimeter accuracy, exhibit complexity similar to that of clinical radiation delivery systems, including image guidance, robotic stage motion, and treatment planning systems. However, physics expertise and resources are scarcer in radiation biology, which makes implementation of conventional prescriptive QA infeasible. In this study, we apply the failure modes and effect analysis (FMEA) popularized by the AAPM task group 100 (TG-100) report to IGSAI and radiation biological research.
Radiation biological research requires a change in paradigm where small errors to large populations of animals are more severe than grievous errors that only affect individuals. To this end, we created a new adverse effects severity table adapted to radiation biology research based on the original AAPM TG-100 severity table. We also produced a process tree which outlines the main components of radiation biology studies performed on an IGSAI, adapted from the original clinical IMRT process tree from TG-100. Using this process tree, we created and distributed a preliminary survey to eight expert IGSAI operators in four institutions. Operators rated proposed failure modes for occurrence, severity, and lack of detectability, and were invited to share their own experienced failure modes. Risk probability numbers (RPN) were calculated and used to identify the failure modes which most urgently require intervention.
Surveyed operators indicated a number of high (RPN >125) failure modes specific to small animal irradiators. Errors due to equipment breakdown, such as loss of anesthesia or thermal control, received relatively low RPN (12-48) while errors related to the delivery of radiation dose received relatively high RPN (72-360). Errors identified could either be improved by manufacturer intervention (e.g., electronic interlocks for filter/collimator) or physics oversight (errors related to tube calibration or treatment planning system commissioning). Operators identified a number of failure modes including collision between the collimator and the stage, misalignment between imaging and treatment isocenter, inaccurate robotic stage homing/translation, and incorrect SSD applied to hand calculations. These were all relatively highly rated (90-192), indicating a possible bias in operators towards reporting high RPN failure modes.
The first FMEA specific to radiation biology research was applied to image-guided small animal irradiators following the TG-100 methodology. A new adverse effects severity table and a process tree recognizing the need for a new paradigm were produced, which will be of great use to future investigators wishing to pursue FMEA in radiation biology research. Future work will focus on expanding scope of user surveys to users of all commercial IGSAI and collaborating with manufacturers to increase the breadth of surveyed expert operators.
图像引导小动物辐照仪（IGSAI）越来越多地被应用于放射生物学研究。这些旨在以亚毫米精度提供辐射的动物辐照仪，其复杂性与临床辐射输送系统相似，包括图像引导、机器人台运动和治疗计划系统。然而，放射生物学中的物理专业知识和资源较为稀缺，这使得传统的规定性 QA 无法实施。在这项研究中，我们将 AAPM 工作组 100（TG-100）报告中普及的失效模式和影响分析（FMEA）应用于 IGSAI 和放射生物学研究。
放射生物学研究需要改变范式，即对大量动物的小误差比仅影响个体的严重错误更为严重。为此，我们根据原始 AAPM TG-100 严重程度表，创建了一个新的适用于放射生物学研究的不良影响严重程度表。我们还根据 TG-100 的原始临床 IMRT 过程树，制作了一个概述在 IGSAI 上进行的放射生物学研究主要组成部分的过程树。使用这个过程树，我们向四个机构的八名专家 IGSAI 操作人员创建并分发了一份初步调查。操作人员对拟议的发生、严重程度和检测不到的失效模式进行了评分，并被邀请分享自己经验过的失效模式。计算了风险概率数（RPN），并用于确定最需要干预的失效模式。
接受调查的操作人员表示，有许多特定于小动物辐照仪的高（RPN>125）失效模式。由于设备故障（例如麻醉或热控制丢失）引起的错误得到的 RPN 相对较低（12-48），而与辐射剂量输送相关的错误得到的 RPN 相对较高（72-360）。可通过制造商干预（例如，过滤器/准直器的电子互锁）或物理监督（与管校准或治疗计划系统调试相关的错误）来改进识别出的错误。操作人员确定了一些失效模式，包括准直器与台架之间的碰撞、成像与治疗等中心之间的失准、机器人台架的不准确归位/平移以及手动计算中应用的不正确 SSD。这些都得到了较高的评分（90-192），这表明操作人员可能存在报告高 RPN 失效模式的偏向。
根据 TG-100 方法，首次将专门针对放射生物学研究的 FMEA 应用于图像引导小动物辐照仪。生成了一个新的不良影响严重程度表和一个过程树，认识到需要一种新的范式，这将对未来希望在放射生物学研究中进行 FMEA 的研究人员非常有用。未来的工作将侧重于扩大用户调查的范围，涵盖所有商业 IGSAI 的用户，并与制造商合作，扩大调查专家操作人员的范围。
