Yamamoto Seiichi, Yabe Takuya, Akagi Takashi, Yamaguchi Mitsutaka, Kawachi Naoki, Kamada Kei, Yoshikawa Akira, Kataoka Jun
Faculty of Science and Engineering, Waseda University, Japan.
Takasaki Institute of Advanced Quantum Science, Foundational Quantum Technology Research Directorate, National Institutes for Quantum Science and Technology (QST), Japan.
Phys Med. 2023 May;109:102592. doi: 10.1016/j.ejmp.2023.102592. Epub 2023 Apr 19.
Prompt secondary electron bremsstrahlung X-ray (prompt X-ray) imaging using a low-energy X-ray camera is a promising method for observing a beam shape from outside the subject. However, such imaging has so far been conducted only for pencil beams without a multi-leaf collimator (MLC). The use of spread-out Bragg peak (SOBP) with an MLC may increase the scattered prompt gamma photons and decrease the contrast of the images of prompt X-rays. Consequently, we performed prompt X-ray imaging of SOBP beams formed with an MLC. This imaging was carried out in list mode during irradiation of SOBP beams to a water phantom. An X-ray camera with a 1.5-mm diameter as well as 4-mm-diameter pinhole collimators was used for the imaging. List mode data were sorted to obtain the SOBP beam images as well as energy spectra and time count rate curves. Due to the high background counts from the scattered prompt gamma photons penetrating the tungsten shield of the X-ray camera, the SOBP beam shapes were difficult to observe with a 1.5-mm-diameter pinhole collimator. With the 4-mm-diameter pinhole collimators, images of SOBP beam shapes at clinical dose levels could be obtained with the X-ray camera. The use of a 4-mm-diameter pinhole collimator attached to the X-ray camera is effective for prompt X-ray imaging with high sensitivity and low background counts. This approach makes it possible to image SOBP beams with an MLC when the counts are low and the background levels are high.
使用低能X射线相机进行瞬发二次电子轫致辐射X射线（瞬发X射线）成像是一种从体外观察束流形状的有前景的方法。然而，迄今为止，此类成像仅针对没有多叶准直器（MLC）的笔形束进行。使用带有MLC的扩展Bragg峰（SOBP）可能会增加散射的瞬发伽马光子，并降低瞬发X射线图像的对比度。因此，我们对由MLC形成的SOBP束进行了瞬发X射线成像。此成像在向水模体照射SOBP束期间以列表模式进行。使用了一个直径为1.5毫米以及带有4毫米直径针孔准直器的X射线相机进行成像。对列表模式数据进行排序以获得SOBP束图像以及能谱和时间计数率曲线。由于穿透X射线相机钨屏蔽的散射瞬发伽马光子产生的高背景计数，使用1.5毫米直径的针孔准直器很难观察到SOBP束的形状。使用4毫米直径的针孔准直器时，可以用X射线相机获得临床剂量水平下SOBP束形状的图像。将直径为4毫米的针孔准直器连接到X射线相机上，对于高灵敏度和低背景计数的瞬发X射线成像是有效的。当计数较低且背景水平较高时，这种方法使得对带有MLC的SOBP束进行成像成为可能。
