Abstract Background Quantifying acute hypoxia is desirable yet challenging in radiation therapy. Here, we report a simulation study on the feasibility of mapping acute hypoxia, generated in a 2D simulation vasculature of a pancreas model, using in situ 15O washout images. The influence of varying tissue types and photon beam energies (i.e., 20, 25, 30 and 50 MeV) was investigated. Method and materials An ex vivo autoradiography 64Cu-ATSM image of a rat tumor was used as a surrogate for the microvessel density map. It was then input to a reaction diffusion model to simulate a steady state partial oxygen pressure (pO2) map. The resulting in situ 15O-PET image was generated using a high-energy photon beam and included both mobile and immobile 15O. An image of 15O washout was produced by subtracting the immobile decay portion from the overall decay curve in the in situ PET image, (i.e., fitting the sum of the two exponentials for mobile and immobile oxygen) using different decay constants. Finally, the pO2 map and in situ 15O washout images were thresholded and compared. Results The reaction diffusion model showed a heterogeneous distribution of pO2 with mean values of 27.4 and 16.8 mmHg, depending on microvessel permeability, tumor vasculature structure, and architecture. A 62% threshold of the mean intensity in the in situ 15O washout image was found to agree reasonably well with the original hypoxia map using 5 mmHg as a cutoff value. These parameters yielded two sets of images with hypoxia fractions of 0.146 and 0.152, respectively. Conclusions This simulation study demonstrates the feasibility of mapping acute hypoxia using tissue in situ activation with high-energy photons. With recent advances in in-room or in-beam PET and more work being performed on thresholding the in situ 15O washout, mapping acute hypoxia in real time may become a reality.

中文翻译：

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用光子束原位激活 15O 绘制瞬态缺氧：模拟研究

摘要背景量化急性缺氧在放射治疗中是可取的，但具有挑战性。在这里，我们报告了使用原位 15O 冲洗图像绘制在胰腺模型的 2D 模拟脉管系统中生成的急性缺氧的可行性的模拟研究。研究了不同组织类型和光子束能量（即 20、25、30 和 50 MeV）的影响。方法和材料 大鼠肿瘤的离体放射自显影 64Cu-ATSM 图像用作微血管密度图的替代物。然后将其输入反应扩散模型以模拟稳态氧分压 (pO2) 图。所得的原位 15O-PET 图像是使用高能光子束生成的，包括可移动和不可移动的 15O。通过使用不同的衰减常数从原位 PET 图像中的整体衰减曲线中减去固定衰减部分（即拟合可移动和固定氧气的两个指数之和），产生 15O 冲刷图像。最后，对 pO2 图和原位 15O 冲洗图像进行阈值处理和比较。结果 反应扩散模型显示 pO2 的不均匀分布，平均值为 27.4 和 16.8 mmHg，具体取决于微血管通透性、肿瘤血管结构和结构。发现原位 15O 冲洗图像中平均强度的 62% 阈值与使用 5 mmHg 作为截止值的原始缺氧图相当吻合。这些参数产生了两组缺氧分数分别为 0.146 和 0.152 的图像。结论 该模拟研究证明了使用高能光子的组织原位激活绘制急性缺氧图的可行性。随着室内或光束内 PET 的最新进展以及对原位 15O 冲洗阈值化进行的更多工作，实时绘制急性缺氧图可能成为现实。