Siegel J A, Zeiger L S, Order S E, Wallner P E
Department of Radiation Oncology, Cooper Hospital/University Medical Center, Camden, NJ 08103.
Int J Radiat Oncol Biol Phys. 1995 Feb 15;31(4):953-8. doi: 10.1016/0360-3016(94)00464-1.
To perform bremsstrahlung single photon emission computed tomographic (SPECT) imaging using 32P chronic phosphate for volume and activity quantitation to calculate absorbed dose estimates.
Seven cancer patients enrolled in clinical Phase I therapeutic protocols were injected with 2.5 million particles of macroaggregated albumin, followed by colloidal 32P chromic phosphate by direct interstitial injection into the tumor-bearing region under computed tomographic (CT) guidance. SPECT images were obtained in these patients. The patient body contour was defined through the use of two externally placed Compton backscatter 99mTc sources. A computer algorithm was written to facilitate region-of-interest volume and activity determination on the reconstructed SPECT slices based on a fixed threshold method. Three sequential SPECT studies were acquired in two of these patients, to determine the accuracy of activity quantitation for bremsstrahlung SPECT studies using Chang's postprocessing method of attenuation compensation with a computer-generated body contour based on the Compton backscatter sources, and an experimentally measured effective linear attenuation coefficient for 32P. The serial data in these two patients were used to calculate absorbed dose estimates.
The 99mTc backscatter sources enabled the patient body outline to be clearly visualized in all the transaxial reconstructed slices and did not contribute significant counts to the patient 32P counts. The calculated activities from the SPECT studies were within 7.8% of the administered 32P activity. The two calculated patient absorbed doses were 4.2 x 10(3) Gy and 5.9 x 10(3) Gy for injected activities of 736 MBq and 920 MBq, respectively.
We conclude that accurate quantitative bremsstrahlung SPECT imaging, for the case of high contrast well-localized activity distributions, with a commercially available postprocessing attenuation correction algorithm, can be performed in a clinical setting. Entirely SPECT-based measurements can be used to generate absorbed dose estimates.
使用32P慢性磷酸盐进行轫致辐射单光子发射计算机断层扫描（SPECT）成像，以进行体积和活度定量，从而计算吸收剂量估计值。
7名参加临床I期治疗方案的癌症患者被注射了250万个大颗粒白蛋白，随后通过在计算机断层扫描（CT）引导下直接间质注射胶体32P铬磷酸盐到肿瘤所在区域。对这些患者进行了SPECT成像。通过使用两个外部放置的康普顿背散射99mTc源来确定患者身体轮廓。编写了一种计算机算法，以基于固定阈值方法促进在重建的SPECT切片上进行感兴趣区域的体积和活度测定。在其中两名患者中进行了三次连续的SPECT研究，以使用基于康普顿背散射源的计算机生成身体轮廓以及实验测量得到的32P有效线性衰减系数，通过Chang的衰减补偿后处理方法来确定轫致辐射SPECT研究中活度定量的准确性。利用这两名患者的系列数据来计算吸收剂量估计值。
99mTc背散射源使患者身体轮廓在所有轴向重建切片中都能清晰可见，并且对患者的32P计数贡献不大。SPECT研究计算得到的活度在给药的32P活度的7.8%以内。对于注射活度分别为736 MBq和920 MBq的情况，两名患者计算得到的吸收剂量分别为4.2×10(3) Gy和5.9×10(3) Gy。
我们得出结论，对于高对比度且定位良好的活度分布情况，使用市售后处理衰减校正算法可以在临床环境中进行准确的定量轫致辐射SPECT成像。完全基于SPECT的测量可用于生成吸收剂量估计值。
