Determination of optimal imaging time of ^99mTc-IDA-D-[c(RGDfK)]₂, a novel integrin α_vβ₃-binding peptide in patients with lung cancer

Objectives ^99mTc-IDA-D-[c(RGDfK)])]₂ (^99mTc-RGD) was developed for targeting tumor-angiogenesis and is a promising agent for cancer imaging. In this study, the optimal imaging time of ^99mTc-RGD was investigated in patients with lung cancer.

Methods Five lung cancer patients (M:F=4:1, 63.6±6.2 yrs, 66.8±15.2 kg) who were identified by PET/CT scan were enrolled in this study. For all patients, Gamma camera planar images were obtained from head to upper thigh at 0, 10, 20 and 60 min post-injection of ^99mTc-RGD. Injected dose was 645±67 MBq. The anterior and posterior images were averaged geometrically, and regions of interest were drawn on the lung cancer regions. The other region of interest was selected on the contralateral site of lung cancer region to assess tumor to non-tumor count density ratio. The tumor to non-tumor ratio was assessed from serial planar images and regions of interests. The time at the highest ratio will be selected as optimal time to imaging for ^99mTc-RGD. Integrin expression was evaluated with immunohistochemistry.

Results Three patients were confirmed as adenocarcinoma, one patient had squamous cell carcinoma and the other had poorly differentiated carcinoma. T stage was from 1b to 2b and only one patient had lymph node metastasis (N1). Cancer regions were clearly identified in four of five patients. For four patients, tumor to non-tumor ratio was assessed according to time, and the ratio was highest at the last scan (40-60 min). The tumor uptake was decreased as time goes by, however non-tumor uptake was decreased faster. Three patient with high tumor to non-tumor ratio (>1.3) had hypermetabolism on FDG PET/CT (>10.o SUV) and high integrin expression.

Conclusions ^99mTc-RGD imaging can evaluate the expression of integrin by imaging. It could give important information for clinical decision and developing new treatment.