PREDICTION OF RADIOTHERAPEUTIC EFFECTS ON TUMOR USING POSITRON EMISSION TOMOGRAPHY

为了评估18f -氟米唑（FMISO）的肿瘤成像潜力，我们在实验肿瘤模型中研究了FMISO的摄取，并检测了FMISO与14c -2-脱氧葡萄糖（2DG）和14c -蛋氨酸（Met）在肿瘤内分布的相关性。方法：在局部缺氧条件下，对AH109A肿瘤对照大鼠和同一肿瘤大鼠的病变分布及双示踪放射自显影进行研究。结果：FMISO在注射后30 ~ 2小时内，肿瘤对FMISO的摄取恒定，2 ~ 4小时内，肿瘤与肌肉的比值为2。计划在2小时进行FMISO肿瘤研究。双示踪放射自显影显示，在FMISO摄取高的区域，Met摄取低，而FMISO摄取低的区域，Met摄取高。FMISO显示坏死区周围肿瘤边缘呈高颗粒密度。2DG在整个活细胞切片上分布更为均匀。低氧、耐辐射肿瘤对FMISO的平均摄取显著高于对照组（p<0.05），对照组对2DG和Met的摄取均高于低氧肿瘤。在检查单个肿瘤时，FMISO的摄取与Met的摄取呈负相关（r=-0.507, p<0.02），而2DG的摄取几乎一致，与FMISO无显著相关性。结论：在我们的模型中，缺氧和耐辐射肿瘤可以通过FMISO摄取增加来识别，这与其他研究一致。我们发现FMISO和2DG在肿瘤内的分布有很大的重叠，而FMISO和Met的分布只有很小的重叠。在PET或SPECT研究中，FMISO联合其他示踪剂可能比单一示踪剂研究更有助于预测肿瘤组织对放疗的反应。

To evaluate tumor imaging potential of 18F-fluoromisonidazole (FMISO), we studied FMISO uptake in an experimental tumor model and examined the correlation between intra-tumoral distributions of FMISO, 14C-2-deoxyglucose (2DG) and 14C-methionine (Met). Methods: We studied the issue distribution and double tracer autoradiography using control rats with AH109A tumor and rats with the same tumor under local hypoxia. Results: Tumor uptake of FMISO was constant between 30 min to 2 hr after injection, and the tumor to muscle ratio was 2, from 2 to 4 hr. A tumor study with FMISO was scheduled at 2 hr. Double tracer autoradiography of the tumor demonstrated that in the areas of high FMISO uptake, there was low uptake of Met, while low FMISO uptake areas showed high Met uptake. FMISO showed high grain density in the rim of the tumor surrounding the necrotic area. 2DG showed more uniform distribution over the entire section of viable cells. The mean uptake of FMISO by hypoxic, radioresistant tumors was significantly higher than the control tumors (p<0.05), while both 2DG and Met uptake by the control tumor were higher than hypoxic tumor. When individual tumors were examined, the uptake of FMISO was inversely correlated with that of Met (r=-0.507, p<0.02), while 2DG showed almost uniform uptake with no significant correlation to FMISO. Conclusions: Hypoxic and radioresistant tumour can be identified by increased FMISO uptake in our model consistent with works reported by others. We found a large overlap in the distribution of FMISO and 2DG within the tumor, but only a small overlap in the distribution of FMISO and Met. A combination of FMISO and other tracers in PET or SPECT study would possibly be more helpful than single tracer study in predicting the response of tumor tissues to radiotherapy.