Princess Margaret Cancer Centre, University Health Network, Toronto, Canada; Techna Institute, University Health Network, Toronto, Canada; Department of Medical Biophysics, University of Toronto, Canada.
Princess Margaret Cancer Centre, University Health Network, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada.
Phys Med. 2022 Jan;93:1-7. doi: 10.1016/j.ejmp.2021.11.009. Epub 2021 Dec 8.
Tumor hypoxia is defined as a low oxygen level in tissue and is associated with poor clinical outcome after chemo-/radiotherapy and surgery in many solid tumor types. Positron Emission Tomography (PET) imaging provides a non-invasive means of measuring local variations in the uptake of hypoxia-targeted agents (e.g. FAZA or FMISO). Accurate quantification of uptake is critically dependent on the PET scanner's linear count rate performance. In the context of cervix cancer, high PET agent accumulation in the bladder, low uptake in the tumor, and their relative proximity makes an accurate quantification of the tumor's hypoxic fraction challenging. The purpose of this study was to estimate the impact of PET scanner non-linearity on PET-based estimation of hypoxic fraction.
The impact of PET scanner non-linearity effect was assessed with a NEMA body phantom, using the cylinder as the "bladder-mimicking" compartment and the water filled background as a surrogate region for the tumor. A simple model of the non-linearity effect was then applied to a set of patient-derived FAZA-PET scans (N = 38) to estimate the impact of the non-linearity on the calculated hypoxic fraction (HF) for each patient.
The NEMA body phantom measurements revealed a substantial overestimate of activity outside the injected "bladder mimicking" cylinder compartment. This uptake resulted in an overestimate in activity between 1.9 and 0.3 kBq/cc corresponding to distances from 1.0 - 7.0 cm from the cylinder. In the patient-derived PET images, the bladder-to-tumor distance ranged between 1.0 and 3.0 cm. For the 38 patients analyzed, the HF was demonstrated to decrease by 1.1-75.0 % [median 27.2 %] depending on distance and relative uptake levels. Additionally, the magnitude of the effect of the non-linearity was found to depend on the pre-scanning hydration protocol employed (p = 0.0065).
Hypoxia imaging of tumors of the cervix is challenging due to patient specific activity accumulation in the bladder and the non-linear response of PET scanner performance. This can result in a substantial overestimate of the calculated hypoxic fraction in cervical tumors. Additional effort needs to be invested to improve the linearity of PET scanners in anatomical regions proximal to the bladder.
肿瘤缺氧定义为组织中的低氧水平，与许多实体肿瘤类型的化疗/放疗和手术后的不良临床结果相关。正电子发射断层扫描（PET）成像提供了一种非侵入性的方法来测量缺氧靶向剂（例如 FAZA 或 FMISO）摄取的局部变化。摄取的准确量化严重依赖于 PET 扫描仪的线性计数率性能。在宫颈癌的情况下，膀胱中高的 PET 药物积累、肿瘤中低摄取以及它们的相对接近使得准确量化肿瘤的缺氧分数具有挑战性。本研究的目的是估计 PET 扫描仪非线性对基于 PET 的缺氧分数估计的影响。
使用 NEMA 体模评估 PET 扫描仪非线性效应，使用圆柱体作为“膀胱模拟”腔室，用水填充背景作为肿瘤的替代区域。然后，将简单的非线性效应模型应用于一组患者衍生的 FAZA-PET 扫描（N=38），以估计非线性对每位患者计算的缺氧分数（HF）的影响。
NEMA 体模测量显示，在注入的“膀胱模拟”圆柱体腔室外的活性存在显著高估。这种摄取导致在距离圆柱体 1.0-7.0 cm 的范围内活性的高估在 1.9 和 0.3 kBq/cc 之间。在患者衍生的 PET 图像中，膀胱与肿瘤之间的距离在 1.0 和 3.0 cm 之间。对于分析的 38 名患者，HF 显示取决于距离和相对摄取水平，降低 1.1-75.0%[中位数 27.2%]。此外，还发现非线性效应的大小取决于使用的预扫描水合方案（p=0.0065）。
由于患者特定的膀胱活性积累和 PET 扫描仪性能的非线性响应，宫颈肿瘤的缺氧成像具有挑战性。这可能导致宫颈肿瘤中计算的缺氧分数的大幅高估。需要投入额外的努力来改善靠近膀胱的解剖区域的 PET 扫描仪的线性度。
