论文标题
来自Varian Probeam Pencil铅笔梁扫描系统的250 MEV质子的表征用于闪光疗法
Characterization of 250 MeV protons from Varian ProBeam pencil beam scanning system for FLASH radiation therapy
论文作者
论文摘要
最近，已经提出了从回旋子提取最高能量以最大化剂量速率（DR）的情况下提出最高能量的情况。即使我们的质子铅笔梁扫描系统可以传递250 MEV（最高能量），但使用250 MeV质子进行常规临床处理并不是典型的，并且在调试中可能没有这种250 MEV的特征。在这项研究中，我们旨在表征来自Varian Probeam系统的250个MEV质子，以评估临床监测电离室（MIC）的闪光处理能力。我们测量了光束调试所需的数据：积分深度剂量（IDD）曲线，点sigma和绝对剂量校准。为了评估麦克风，我们测量了输出作为梁电流的函数。为了表征250 MEV闪光灯，我们测量了：（1）中央轴DR是电流和点间距和布置的函数，（2）对于固定点间距，最大场大小仍然可以实现闪光灯DR（即> 40 gy/s），（3）DR可重复性。所有Flash DR测量均使用离子室进行绝对剂量进行，并从日志文件中获得辐照时间。我们使用EBT-XD膜和辐照时间验证了剂量测量值，并使用快速的像素化光谱检测器进行了测量。 IDD的R90和R80分别为37.58和37.69 cm，同中心的Spot Sigma分别为σx= 3.336和σY= 3.332 mm。对于调试条件，将绝对剂量输出测量为0.377 Gye*mm2/mu。对于高达15 Na的梁电流的输出稳定，对于115 Na，它逐渐增加到12倍。 DR取决于梁电流，点间距和排列，并且可以在4.2％的变化范围内复制。即使达到了Flash，并且提供Flash DR的最大场地被确定为35x35 mm2，但当前的麦克风具有DR依赖性，用户应每次为其Flash应用程序测量DR。
Recently, shoot-through proton FLASH has been proposed where the highest energy is extracted from the cyclotron to maximize the dose rate (DR). Even though our proton pencil beam scanning system can deliver 250 MeV (the highest energy), it is not typical to use 250 MeV protons for routine clinical treatments and as such 250 MeV may not have been characterized in the commissioning. In this study, we aim to characterize 250 MeV protons from Varian ProBeam system for FLASH RT as well as assess the ability of clinical monitoring ionization chamber (MIC) for FLASH-readiness. We measured data needed for beam commissioning: integral depth dose (IDD) curve, spot sigma, and absolute dose calibration. To evaluate MIC, we measured output as a function of beam current. To characterize a 250 MeV FLASH beam, we measured: (1) central axis DR as a function of current and spot spacing and arrangement, (2) for a fixed spot spacing, the maximum field size that still achieves FLASH DR (i.e., > 40 Gy/s), (3) DR reproducibility. All FLASH DR measurements were performed using ion chamber for the absolute dose and irradiation times were obtained from log files. We verified dose measurements using EBT-XD films and irradiation times using a fast, pixelated spectral detector. R90 and R80 from IDD were 37.58 and 37.69 cm, and spot sigma at isocenter were σx=3.336 and σy=3.332 mm, respectively. The absolute dose output was measured as 0.377 GyE*mm2/MU for the commissioning conditions. Output was stable for beam currents up to 15 nA, and it gradually increased to 12-fold for 115 nA. DR depended on beam current, spot spacing and arrangement and could be reproduced within 4.2% variations. Even though FLASH was achieved and the largest field size that delivers FLASH DR was determined as 35x35 mm2, current MIC has DR dependence and users should measure DR each time for their FLASH applications.
