Shen S, DeNardo G L, Yuan A, DeNardo D A, DeNardo S J
University of California at Davis, School of Medicine, Sacramento.
J Nucl Med. 1994 Aug;35(8):1381-9.
Yttrium-90 is a promising radionuclide for radioimmunotherapy of cancer because of its energetic beta emissions. Therapeutic management requires quantitative imaging to assess the pharmacokinetics and radiation dosimetry of the 90Y-labeled antibody. Conventional gamma photon imaging methods cannot be easily applied to imaging of 90Y-bremsstrahlung because of its continuous energy spectrum.
The sensitivity, resolution and source-to-background signal ratio (S/B) of the detector system for 90Y-bremsstrahlung were investigated for various collimators and energy windows in order to determine optimum conditions for quantitative imaging. After these conditions were determined, the accuracy of quantitation of 90Y activity in an Alderson abdominal phantom was examined.
When the energy-window width was increased, the benefit of increased sensitivity outweighed degradation in resolution and S/B ratio until the manufacturer's energy specifications for the collimator were exceeded. Using the same energy window, we improved resolution and S/B for the medium-energy (ME) collimator when compared to the low-energy, all-purpose (LEAP) collimator, and there was little additional improvement using the high-energy (HE) collimator. Camera sensitivity under tissue equivalent conditions was 4.2 times greater for the LEAP and 1.7 times greater for the ME collimators when compared to the HE collimator. Thus, the best, most practical selections were found to be the ME collimator and an energy window of 55-285 keV. When we used these optimal conditions for image acquisition, the estimation of 90Y activity in organs and tumors was within 15% of the true activities.
The results of this study suggest that reasonable accuracy can be achieved in clinical radioimmunotherapy using 90Y-bremsstrahlung quantitation.
钇-90因其高能β发射，是一种很有前景的用于癌症放射免疫治疗的放射性核素。治疗管理需要进行定量成像，以评估90Y标记抗体的药代动力学和辐射剂量学。由于其连续能谱，传统的γ光子成像方法不易应用于90Y轫致辐射成像。
研究了90Y轫致辐射探测器系统在各种准直器和能量窗下的灵敏度、分辨率和源本底信号比（S/B），以确定定量成像的最佳条件。确定这些条件后，检查了Alderson腹部模型中90Y活度定量的准确性。
当能量窗宽度增加时，灵敏度增加的益处超过了分辨率和S/B比的降低，直到超过准直器的制造商能量规格。使用相同的能量窗，与低能通用（LEAP）准直器相比，我们提高了中能（ME）准直器的分辨率和S/B，使用高能（HE）准直器几乎没有额外的改善。与HE准直器相比，在组织等效条件下，LEAP准直器的相机灵敏度高4.2倍，ME准直器高1.7倍。因此，发现最佳、最实用的选择是ME准直器和55-285 keV的能量窗。当我们使用这些最佳条件进行图像采集时，器官和肿瘤中90Y活度的估计值在真实活度的15%以内。
本研究结果表明，使用90Y轫致辐射定量在临床放射免疫治疗中可实现合理的准确性。
