Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
Department of Radiation Oncology, Perelman Center for Advanced Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA.
Med Phys. 2020 Apr;47(4):1871-1879. doi: 10.1002/mp.14070. Epub 2020 Feb 21.
To accomplish novel radiation treatment techniques in preclinical radiation research, small animal image-guided radiotherapy systems have been increasingly integrated into preclinical radiation research over the last decade. Although such systems have sophisticated tools (such as cone-beam computed tomography-based image guidance, robotic couch, treatment planning system (TPS), and electronic portal imaging devices [EPIDs]). To our knowledge, no established technique can perform independent and online verification of the delivered dose during radiotherapy. In this study, we implement an online EPID dosimetry for each administered SA-IGRT fraction in a rat orthotopic model of prostate cancer.
To verify the accuracy of delivered dose to rat, we compared the two-dimensional (2D) calculated dose distribution by TPS as the planned dose, with online dose distribution estimated using an EPID as the delivered dose. Since image acquisition software was not capable of acquiring integrated images over a long period of time, we used the EPID to estimate dose rate rather than dose. The central axis (CAX) dose rate values at the beam's exit surface were compared. In addition, 2D dose distributions were also compared under different gamma criteria. To verify the accuracy of our EPID dosimetry technique, we measured transit and exit doses with film during animal treatment. In this study, 20-mm cone was used to collimate beam. We previously observed that the EPID response was independent of collimator size for collimator size ≥15-mm, we did not apply for additional correction factor.
Comparison of exit CAX dose rate values of TPS-calculated and EPID-estimated showed that the average difference was 3.1%, with a maximum of 9.3%. Results of gamma analysis for 2D comparison indicated an average of 90% passing rate with global gamma criterion of 2 mm/5%. We observed that TPS could not calculate dose accurately in peripheral regions in which the penumbra effect was dominant. Dose rate values estimated by EPID were within 2.1% agreement with film at both the imager plane and the beam's exit surface for 4 randomly selected animals for which film measurement verification was performed.
The small animal radiation research platform (SARRP) system's built-in EPID was utilized to estimate dose delivered to rats at kilovoltage energy x-rays. The results of this study suggest that the EPID is an invaluable tool for verifying delivered dose to small animal to help validate conclusions made from preclinical radiation research.
在过去十年中，为了实现临床前放射研究中的新型放射治疗技术，小型动物图像引导放射治疗系统已越来越多地融入临床前放射研究中。尽管这些系统具有复杂的工具（例如基于锥形束计算机断层扫描的图像引导，机器人床，治疗计划系统（TPS）和电子射野影像装置[EPID]）。据我们所知，尚无既定技术可在放射治疗过程中对所给予剂量进行独立和在线验证。在这项研究中，我们在前列腺癌的大鼠原位模型中对每个进行的 SA-IGRT 分数实施了在线 EPID 剂量测定。
为了验证大鼠所给予剂量的准确性，我们将 TPS 计算的二维（2D）剂量分布与使用 EPID 在线估计的作为所给予剂量的剂量分布进行了比较。由于图像采集软件无法长时间采集综合图像，因此我们使用 EPID 来估计剂量率而不是剂量。比较了光束出射表面上的中心轴（CAX）剂量率值。此外，还根据不同的伽马标准比较了 2D 剂量分布。为了验证我们的 EPID 剂量测定技术的准确性，我们在动物治疗过程中使用胶片测量了传输和出射剂量。在这项研究中，使用 20mm 的圆锥束准直器对光束进行准直。我们之前观察到，对于准直器尺寸≥15mm 的 EPID 响应与准直器尺寸无关，因此我们没有申请额外的校正因子。
TPS 计算的出口 CAX 剂量率值与 EPID 估计值的比较表明，平均差异为 3.1％，最大差异为 9.3％。2D 比较的伽马分析结果表明，在以 2mm/5％的全局伽马标准下，平均通过率为 90％。我们观察到，TPS 在以边缘效应为主的外围区域无法准确计算剂量。对于进行了胶片测量验证的 4 只随机选择的动物，EPID 估计的剂量率值在成像平面和光束出射表面处与胶片的偏差均在 2.1％以内。
利用小型动物放射研究平台（SARRP）系统内置的 EPID 来估算千伏 X 射线照射大鼠时所给予的剂量。这项研究的结果表明，EPID 是一种非常有价值的工具，可用于验证小动物所给予的剂量，有助于验证临床前放射研究的结论。
