Dillehay L E, Mayer R, Zhang Y G, Song S Y, Shao Y, Mackensen D G, Williams J R
Department of Oncology, Johns Hopkins School of Medicine, Baltimore, Maryland.
Cancer. 1994 Feb 1;73(3 Suppl):945-50. doi: 10.1002/1097-0142(19940201)73:3+<945::aid-cncr2820731329>3.0.co;2-1.
Large differences in uptake between tumors, even for the same size, frequently observed in clinical and experimental radioimmunotherapy (RAIT), make monitoring of uptake in individual tumors imperative in comparing protocols. 90Y, widely-used for RAIT, emits no gamma radiation and absorption of the beta particle in tissue makes its detection unsuitable for in vivo monitoring. We tested whether bremsstrahlung radiation, produced when betas are decelerated by nuclei, could be used to monitor tumor uptake.
Subcutaneous human LS174T colon carcinoma tumors were grown in the upper thigh of nude mice and labeled antibody injected intracardially. With the tumor placed in the 2 cm-diameter aperture in a lead collimator, photons with energies from 100 to 200 keV transmitted through plastic, which absorbed the beta particles, were counted to maximize shielding from the rest of the body. The contribution of the normal tissues was subtracted by counting the non-tumor-bearing leg in the same position. Excretion was calculated from whole body activity determined by removing the collimator, placing the mouse in a syringe surrounded by tissue-equivalent material 10 cm from the detector, and counting photons between 200 and 740 keV to minimize the effect of tissue attenuation.
For tumors larger than 0.14 gm, a good correlation was obtained between the in vivo bremsstrahlung measurements and the measurements on excised tumors in a calibrated well counter. Similar excretion rates observed in all the animals suggested that the whole body counting was accurate.
Bremstrahlung detection appears feasible and reliable for monitoring both tumor and whole body activities.
在临床和实验性放射免疫疗法（RAIT）中，即使肿瘤大小相同，其摄取量也常常存在很大差异，这使得在比较不同方案时监测单个肿瘤的摄取情况变得至关重要。广泛用于RAIT的90Y不发射γ射线，且β粒子在组织中的吸收使其检测不适用于体内监测。我们测试了β粒子被原子核减速时产生的轫致辐射是否可用于监测肿瘤摄取。
将皮下人LS174T结肠癌肿瘤接种于裸鼠大腿上部，并经心内注射标记抗体。将肿瘤置于铅准直器直径为2 cm的孔中，对透过塑料（其可吸收β粒子）的能量在100至200 keV之间的光子进行计数，以最大程度屏蔽身体其他部位的辐射。通过对同一位置未接种肿瘤的腿部进行计数来减去正常组织的贡献。通过移除准直器、将小鼠置于距离探测器10 cm且被组织等效材料包围的注射器中，并对200至740 keV之间的光子进行计数以最小化组织衰减的影响，从而根据全身活性计算排泄量。
对于大于0.14 g的肿瘤，体内轫致辐射测量值与校准的井型计数器中切除肿瘤的测量值之间具有良好的相关性。所有动物观察到的排泄率相似，表明全身计数是准确的。
轫致辐射检测对于监测肿瘤和全身活性似乎是可行且可靠的。
