The Role Of ～(11)C-Acetate PET For The Diagnosis Of Neoplasms

Objectives: To study the feasibility of using ¹¹C-Acetate (¹¹C_AC) PET for detecting renal and hepatic neoplasms and to evaluate the clinical effect of ¹¹C-AC used as a complement of ¹⁸FDG.Methods and materials:1. Methods:¹¹C-AC preparation: Carbon-11 was produced using a CTI RDS111 cyclotron and then delivered to an automatic module to synthesize ¹1C-AC. After quality control, ¹1C-AC was ready for clinical use. PET was performed using a SIEMENS ECAT HR+ scanner. A routine ¹⁸FDG PET imaging was performed for all patients, ¹¹C-AC studies consisted of an initial scan on upper abdomen for 10rain and then followed by a whole body scan. Dynamic scans consisted of twenty four 10s frames started simultaneously with ¹¹C-AC injection. SUVs were calculated by ROI method. A lesion was classified "+" by both visual assessment and a semi-quantitative target-background ratio (T/B)＞1, "-" when its activity was same as that in nontumor tissue and T/B≤1.2. Subjects and patients:3 female volunteers undertook PET scans following iv. of 415-814MBq ¹¹C-AC for biodistribution study. Initial scan was taken immediately after injection in 2 cases for upper abdomen and whole body scan was performed 10rain later in all 3. 1 female patient with renal cancer undertook regional dynamic PET scan to derive time-activity changes in liver, pancreas and kidney. The influence of dose on tumor uptake was observed in 1 liver cancer patient who was studied twice (96 and 614MBq ¹¹c-AC) within 3 days.30 patients with 26 primary renal lesions underwent ¹¹C-AC(111-655MBq i.v.) PET imaging and among them 23 underwent ¹⁸FDG PET imaging within one week. 26 primary and 3 metastatic lesions were confirmed histologically. 1 metastasis was proved by CT and clinical follow-up. 13 renal clear cell carcinoma and 6 transitional cell carcinoma lesions had pathologic grading.20 patients suspicious of hepatic neoplasms underwent both ¹⁸FDG and ¹¹C-AC PET within 1 week. 16 patients were proved pathologically and the HCC cases were also classified by grading. 4 patients were confirmed by clinical follow-up (time＞6 months).All patients had CT, MRI, US or SPECT studies.Results:1. ¹¹C-AC production was not stable. The amount of product fluctuated between 0 and 2060MBq..2. Whole body normal distribution:The pancreas showed persistent highest uptake of ¹¹C-AC. Slight activity in the small intestine was observed. High accumulation of radioactivity appeared in renal cortex and myocardium initially but cleared off rapidly thereafter. Liver, spleen and salivary gland showed moderate accumulation of radioactivity. The bladder showed no accumulation.3. Renal neoplasmsSince high accumulation in normal renal cortex cleared off rapidly, most primary renal cell carcinomas showed positive images in delayed scan. In comparison with ¹⁸FDG (30.8% positively), ¹¹C-AC was more sensitive in detecting primary lesions of renal cell carcinoma(76.9% positively). However, ¹⁸FDG was an effective tracer in the diagnosis of transitional cell carcinomas, since 5 (5/5) lesions were all visualized while only 2 (2/6) were demonstrated in ¹¹C-AC imaging. 2 renal angiomyolipomas were both positive in early and delayed imaging of ¹¹C-AC, but ureteritis was negative.4. Hepatic neoplasms:No ¹¹C-AC and ¹⁸FDG uptake were found in 3 benign hepatic lesions. 2 patients with precancerous lesions showed positive uptake of ¹¹C-AC only. 5 patients (3 cholangiocarcinomas, 1 angiosarcoma and 1 metastatic lesion) demonstrated uptake positive with ¹⁸FDG, but negative with ¹¹C-AC. Of 10 HCC patients, 2 well-differentiated lesions were only positive with ¹¹C-AC, 2 poorly differentiated lesions were only positive with ¹⁸FDG, and 6 cases (3 well-differentiated and 3 medially differentiated type) were positive with both.Conclusions:1. The CTI ¹¹C-AC synthesis module is efficient to produce high quality product. But the amount of unstable yields is the main problem to overcome.2. Fasting over 4 hours and resting would be helpful for improving image quality. The high accumulation of ¹¹C-AC in renal cortex initially makes it difficult to detect the lesion. A dose＜185MBq is not suitable for ¹¹C-AC imaging.3.¹¹C-AC is more sensitive than ¹⁸FDG for the detection of well differentiated renal cell carcinoma, especially for Gradeâ… -â…¡, but ¹⁸FDG is still the first choice for the diagnosis of renal neoplasms. The relationship between ¹¹C-AC and ¹⁸FDG is complementary to each other.4. Combination of ¹¹C-AC and ¹⁸FDG, PET is not only useful in increasing the accuracy of diagnosis, differentiating primary or secondary/benign or malignant lesions, but also giving important information for the grading of hepatic carcinoma before using method of invasive intervention.