Enhancing the capability of MAPS for radiotherapy verification

我们开发了一种基于LASSENA单片有源像素传感器的薄的上游设备，用于强度调制放疗的实时二维验证。在强度调制放射治疗中，光束由一堆薄的移动准直器形成，以尽可能多地避开健康组织。该装置非常薄，因此可以放置在光束和患者之间，因为它的衰减小于1%。该设备以前所未有的精度实时报告每个准直器的位置（我们的位置分辨率为146微米，使用仅一秒钟处理产生的数据）和集成信号，给出光束强度的粗略估计。因此，无需事先测量，即可实时验证治疗计划。放射治疗的趋势之一是转向更短但更强烈的治疗。其中一条是无滤光片（FFF）处理。这些治疗提供的剂量率要高得多，因此实时监测治疗更为重要，因为错误可能造成严重后果。我们目前基于lassena的系统不适合FFF治疗。一种新的传感器雅典娜已经被开发出来。在本提案中，我们希望在临床环境中描述雅典娜，并证明它至少与LASSENA一样有效，即使对于FFF治疗也是如此。在正常的临床操作中，我们的设备每年将接受约5kGy的综合辐射剂量。我们希望对雅典娜进行辐射测试，以确定其临床寿命，以确保雅典娜设备作为产品是可行的。LASSENA不能测量给病人的剂量。这是因为装置中的信号是由治疗光子和污染电子产生的信号的结果。后者是由光子与放射治疗机中的空气和材料相互作用产生的。电子信号依赖于许多部分未知的参数，因此不能用简单的方法去除。我们发明了一种同时测量电子和光子贡献的方法，通过在传感器的衬底上进行图案化。我们成功地完成了原理测量的证明，并证明了该方法的有效性。已经提出了专利申请。在本项目中，我们希望优化设计并确定剂量测量精度。LASSENA系统能够实时报告准直器位置。整个算法在LASSENA传感器的前身——Achilles的DAQ系统固件中实现。在这个项目中，我们将把固件从阿喀琉斯系统调整到雅典娜系统。项目完成后，我们将生产一个系统，可以实时监测准直器的位置和给病人的剂量。这大大提高了患者的安全性，因为如果测量的治疗不符合计划的治疗，光束可以在几秒钟内停止。这样的系统对NHS也有很大的好处，因为在实际治疗之前不需要测量（幻影运行）。因此，更多的患者可以在同一时间得到安全的治疗。

We have developed a thin, upstream device for real time 2D verification of intensity modulated radiotherapy based on the LASSENA monolithic active pixel sensor. In intensity modulated radiotherapy, the beam is shaped by a stack of thin moving collimators to spare as much of the healthy tissue as possible. The device is very thin and can therefore be placed between the beam and the patient as its attenuation is less than 1%. The device reports the position of each of the collimators in real time with unprecedented precision (our position resolution is 146 micron using the data generated in only one second of treatment) and an integrated signal, which gives a crude estimate of the beam intensity. Thus the treatment plan can be verified in real time without prior measurements. One of the trends in radiotherapy is to move to shorter but more intense treatments. One strand of this is Flattening Filter Free (FFF) treatments. These treatments provide a much higher dose rate and therefore it is even more important to monitor the treatment in real time as errors can have grave consequences. Our current LASSENA-based system is not suitable for FFF treatments. A new sensor has been developed, the Athena. In this proposal we want to characterise the Athena in a clinical setting and demonstrate that it works at least as well as the LASSENA, even for FFF treatments. In normal clinical operation our device would receive an integrated radiation dose of around 5kGy per year. We want to perform a radiation test of the Athena to find its clinical lifetime to ensure that the Athena based device is viable as a product. The LASSENA is not able to measure the dose administrated to the patient. This is because the signal in the device is the result of signal generated by the therapeutic photons and contamination electrons. The latter are generated by interactions of the photons with air and materials in the radiotherapy machine. The electron signal is dependent on many and partly unknown parameters and thus cannot be removed in a simple way. We have invented a way to measure simultaneously the electron and the photon contribution separately by patterning the substrate of the sensor. We successfully completed proof of principle measurements and showed that the method works. A patent application has been made. In this project we want to optimise the design and determine the dose measurement precision. The LASSENA system is able to report the collimator positions in real time. The whole algorithm was implemented in the firmware for the DAQ system for a predecessor of the LASSENA sensor, the Achilles. In this project we will adapt the firmware from the Achilles system to the Athena system.After completion of the project, we will have produced a system that can monitor the collimator positions and the dose administered to the patient in real time. This significantly enhances patient safety as the beam can be stopped within seconds if the measured treatment is not conform the planned treatment. Such a system would also be of great benefit for the NHS as there is no need for measurements (phantom runs) before the actual treatment. Hence, more patients can be safely treated in the same time.