The Usefulness of F-18-FDG PET and The Effect of Scan Protocol in Diagnosis of Intraocular Tumors / 대한핵의학회잡지

PURPOSE: It is important to differentiate malignant from benign lesions of intraocular masses in choosing therapeutic plan. Biopsy of intraocular tumor is not recommended due to the risk of visual damage. We evaluated the usefulness of F-18-FDG PET imaging in diagnosing intraocular neoplasms. MATERIALS AND METHODS: F-l8-FDG PET scan was performed in 13 patients (15 lesions) suspected to have malignant intraocular tumors. There were 3 benign lesions (retinal detachment, choroidal effusion and hemorrhage) and 10 patients with 12 malignant lesions (3 melanomas, 7 retinoblastomas and 2 metastatic cancers). Regional eye images (256*256 and 128*128 matrices) were obtained with or without attenuation correction. Whole body scan was also performed in eight patients (3 benign and 6 malignant lesions). RESULTS: All malignant lesions were visualized while all benign lesions were not visualized. The mean peak standardized uptake value (SUV) of malignant lesions was 2.64+/-0.57 g/ml. There was no correlations between peak SUV and tumor volume. Two large malignant lesions (>1000 mm3 ) showed hot uptake on whole body scan. But two medium-sized lesions (100-l000 mm3) looked faint and two small (<100 mm3) lesions were not visualized. The images reconstructed with 256*256 matrix showed lesions more clearly than those with 128X128 matrix. CONCLUSION: F-18-FDG PET scan is highly sensitivity in detecting malignant intraocular tumor. For the evaluation of small-sized intraocular lesions, whole body scan is not appropriate because of low sensitivity. A regional scan with sufficient acquisition time is recommended for that purpose. Image reconstruction in matrix size of 256*256 produced clearer images than the ones in 128X128, but it does not affect the diagnostic sensitivity.

Radiation Absorbed Dose Measurement after I-131 Metaiodobenzylguanidine Treatment in a patient with Pheochromycytoma / 대한핵의학회잡지

PURPOSE: The measurement of radiation absorbed dose is useful to predict the response after I-131 labeled metaiodobenzylguanidine (MIBG) therapy and determine therapy dose in patients with unresectable or malignant pheochromocytoma. We estimated the absorbed dose in tumor tissue after high dose I-131 MIBG in a patient with pheochromocytoma using a gamma camera and Medical Internal Radiation Dose (MIRD) formula. MATERIALS AND METHODS: A 64-year old female patient with pheochromocytoma who had multiple metastases of mediastinum, right kidney and periaortic lymph nodes, received 74 GBq (200 mCi) of I-131 MIBG. We obtained anterior and posterior images at 0.5, 16, 24, 64 and 145 hours after treatment. Two standard sources of 37 and 74 MBq of I-131 were imaged simultaneously. Cummulated I-131 MIBG uptake in tumor tissue was calculated after the correction of background activity, attenuation, system sensitivity and count loss at a high count rate. RESULTS: The calculated absorbed radiation dose was 32-63 Gy/ 74 GBq, which was lower than the known dose for tumor remission (150-200 Gy). Follow-up studies at 1 month showed minimally reduced tumor size on computed tomography, and mildly reduced I-131 MIBG uptake. CONCLUSION: We estimated radiation absorbed dose after therapeutic I-131 MIBG using a gamma camera and MIRD formula, which can be peformed in a clinical nuclear medicine laboratory. Our RESULTS suggest that the measurement of radiation absorbed dose in I-131 MIBG therapy is feasible as a routine clinical practice that can guide further treatment plan. The accuracy of dose measurement and correlation with clinical outcome should be evaluated further.

Accuracy of 18F FDG PET after Surgery and Radiotherapy in Head and Neck Cancers / 대한핵의학회잡지

PURPOSE: The purpose of this study was to evaluate the diagnostic accuracy of [18F]FDG PET in the diagnosis of recurrent head and neck cancer after the completion of surgery and radiotherapy in patients with head and neck cancers. MATERIALS AND METHODS: In fifty-nine patients with head and neck cancers, whole body [18F]FDG PET studies were performed. According to the different therapeutic modalities, patients were divided into four groups (Group I; pre-treatment, Group II; surgery, Group III; radiotherapy, Group IV; both surgery and radiotherapy). [18F]FDG PET images were compared with clinical, CT and histopathologic findings. RESULTS: For detection of metastatic lymph nodes in 14 patients of pre-treatment group (group I), the sensitivity and specificity of PET were 100% (10/10) and 75% (3/4), and those of CT were 80% (8/10) and 100% (4/4). For detection of recurrence in 45 patients of post-treatment group, overall sensitivity and specificity of PET were 96.2% (25/26) and 78.9% (15/19) [(100% and 75% in group II, 80% and 50% in group III, and 100% and 100% in group IV)] without significant difference from pre-treatment group (p>0.1). In detecting recurrence, the sensitivity and specificity of [18F]FDG PET were 90.9% (10/11) and 20% (1/5) in 16 patients who underwent [18F]FDG PET within 2 months after the completion of treatment. The specificity of these patients was significantly lower than that of 29 patients (100% of sensitivity and specificity) who underwent [18F]FDG PET 2 months after treatment (p<0.05). CONCLUSION: [18F]FDG PET is an accurate diagnostic modality for the detection of recurrence in head and neck cancer. Post-therapy [18F]FDG PET should be obtained at least 2 months after the completion of surgery or radiotherapy.