Estimation and correction of produced light from prompt gamma photons on luminescence imaging of water for proton therapy dosimetry
Estimation and correction of produced light from prompt gamma photons on luminescence imaging of water for proton therapy dosimetry
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DOI：
10.1088/1361-6560/aaa90c
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发表时间：
2018-02-01
影响因子：
3.5
通讯作者：
Yamamoto, Seiichi
中科院分区：
文献类型：
--
作者：
Yabe, Takuya;Komori, Masataka;Yamamoto, Seiichi
虽然在质子束照射过程中使用冷却的电荷耦合器件相机的发光图像的水显示几乎相同的质子束的电离室测量的范围，深度分布显示较低的布拉格峰强度比电离室测量的。此外，在超过布拉格峰深度的深度中观察到宽的光学基线信号。我们假设，这个广泛的基线信号来源于质子诱导的即时伽马光子与水的相互作用。这些瞬发伽马光子与水相互作用以形成高能康普顿电子，这可能导致来自超过布拉格峰位置的深度的发光或切伦科夫发射。为了阐明这一想法，我们测量了水的发光图像，在水中的质子照射时，视差误差最小化，并模拟了由即时伽马光子与水的相互作用产生的光。我们通过减去由水中的即时伽马光子的相互作用产生的光的模拟分布来校正发光图像的测量深度剖面。还使用从水的发光图像的离束区域获得的瞬发伽马光子的光的估计深度剖面进行校正。通过这些校正，我们成功地获得了与质子模拟剂量分布几乎相同的深度分布。校正后的布拉格峰相对于模拟数据的相对高度百分比从未经校正的80%增加到94%。此外，布拉格峰的较深部分的相对偏移高度的百分比从未校正的4%下降到0.2%-0.4%。这些结果表明，水的发光成像的剂量分布测量质子治疗剂量学的潜力。
Although the luminescence images of water during proton-beam irradiation using a cooled charge-coupled device camera showed almost the same ranges of proton beams as those measured by an ionization chamber, the depth profiles showed lower Bragg peak intensities than those measured by an ionization chamber. In addition, a broad optical baseline signal was observed in depths that exceed the depth of the Bragg peak. We hypothesize that this broad baseline signal originates from the interaction of proton-induced prompt gamma photons with water. These prompt gamma photons interact with water to form high-energy Compton electrons, which may cause luminescence or Cherenkov emission from depths exceeding the location of the Bragg peak. To clarify this idea, we measured the luminescence images of water during the irradiations of protons in water with minimized parallax errors, and also simulated the produced light by the interactions of prompt gamma photons with water. We corrected the measured depth profiles of the luminescence images by subtracting the simulated distributions of the produced light by the interactions of prompt gamma photons in water. Corrections were also conducted using the estimated depth profiles of the light of the prompt gamma photons, as obtained from the off-beam areas of the luminescence images of water. With these corrections, we successfully obtained depth profiles that have almost identical distributions as the simulated dose distributions for protons. The percentage relative height of the Bragg peak with corrections to that of the simulation data increased to 94% from 80% without correction. Also, the percentage relative offset heights of the deeper part of the Bragg peak with corrections decreased to 0.2%-0.4% from 4% without correction. These results indicate that the luminescence imaging of water has potential for the dose distribution measurements for proton therapy dosimetry.