Equivalent Dose Rate 1 Meter from Neuroendocrine Tumor Patients Exiting the Nuclear Medicine Department After Undergoing Imaging.

123I-metaiodobenzylguanidine (MIBG) and 111In-pentetrotide SPECT have been used for functional imaging of neuroendocrine tumors (NETs) for the last 2 decades. More recently, PET/CT imaging with 18F-FDG, 18F-fluorodihydroxyphenylalanine (FDOPA), and 68Ga somatostatin-receptor ligands in NETs has been expanding. A literature search could find no direct measurements of the dose rate from NET patients exiting the nuclear medicine department after undergoing PET/CT with 18F-FDOPA or 68Ga-DOTATOC, a somatostatin analog. Methods: We measured the dose rates from 93 NET patients on leaving the department after undergoing PET/CT or SPECT/CT in our centers. In total, 103 paired measurements of equivalent dose rate at 1 m (EDR-1m) from the sternum and urinary bladder were obtained. The detector faced the sternum or bladder and was 1 m away from and directly in front of the patient. The practice for exiting the department differed according to whether the patient had been referred for PET/CT or for SPECT/CT. PET/CT patients were discharged after imaging, whereas SPECT/CT patients left the department earlier, just after radiopharmaceutical injection. Results: The median administered activity was 122 MBq in 53 68Ga-DOTATOC PET/CT studies, 198 MBq in 15 18F-FDOPA PET/CT studies, and 176 MBq in 13 18F-FDG PET/CT studies. The corresponding median EDR-1m was 4.8, 9.5, and 8.8 µSv/h, respectively, facing the sternum, and 5.1, 10.1, and 9.5 µSv/h, respectively, facing the bladder. The median administered activity was 170 MBq in 12 111In-pentetreotide SPECT/CT studies and 186 MBq in 10 123I-MIBG SPECT/CT studies. The corresponding median EDR-1m was 9.4, and 4.9 µSv/h, respectively, at the level of the sternum, and 9.3 and 4.7 µSv/h, respectively, at the level of the bladder. The EDR-1m was less than 20 µSv/h in all patients. Thus, when exiting the nuclear medicine department, the NET patients injected with 68Ga-DOTATOC or 123I MIBG emitted an average EDR-1m roughly half that of patients injected with other radiopharmaceuticals. This finding is a complementary argument for replacing SPECT by PET somatostatin-receptor imaging. Conclusion: Our current practice of allowing patients to exit after PET/CT imaging or just after SPECT radiopharmaceutical injection appears to be safe from a radiation protection point of view. Restrictive advice is unnecessary for NET patients being discharged from the department.

[18F]-NaF PET/CT imaging in cardiac amyloidosis.

Cardiac amyloidosis (CA) is recognized as a common cause of restrictive cardiomyopathy and heart failure due to the deposition of insoluble proteins in the myocardial interstitium. We emphasize the role of [18F]-sodium fluoride (NaF) PET/CT as a potential noninvasive tool to identify and differentiate the transthyretin-related cardiac amyloidosis from the light-chain cardiac amyloidosis. We report cases of a 73-year-old man and a 75-year-old woman followed in our center for congestive heart failure with marked alteration of the left ventricular ejection fraction due to familial transthyretin Val122Ile cardiac amyloidosis and light-chain cardiac amyloidosis, respectively, confirmed on endomyocardial biopsy.

Pretherapy metabolic tumour volume is an independent predictor of outcome in patients with diffuse large B-cell lymphoma.

PURPOSE: We investigated the prognostic value of total metabolic tumour volume (TMTV) in diffuse large B-cell lymphoma (DLBCL). METHODS: TMTV was measured in 114 patients with newly diagnosed DLBCL who underwent (18)F-FDG PET/CT at baseline before immunochemotherapy. TMTV was computed by summing the volumes of all lymphomatous lesions after applying the local SUVmax threshold of 41% using semiautomatic software. Prognostic value was assessed by Kaplan-Meier estimates of progression-free survival (PFS) and overall survival (OS). RESULTS: Median follow-up was 39 months. Average pretherapy TMTV was 509 ± 568 cm(3). The 3-year estimates of PFS were 77 % in the low metabolic burden group (TMTV ≤550 cm(3)) and 60% in the high metabolic burden group (TMTV >550 cm(3), p = 0.04), and prediction of OS was even better (87% vs. 60%, p = 0.0003). Cox regression showed independence of TMTV for OS prediction (p = 0.002) compared with other pretherapy indices of tumour burden, such as tumour bulk and the International Prognostic Index. CONCLUSION: Pretherapy TMTV is an independent predictor of outcome in patients with DLBCL.

Clinical impact of contrast-enhanced computed tomography combined with low-dose (18)F-fluorodeoxyglucose positron emission tomography/computed tomography on routine lymphoma patient management.

This study evaluated the clinical impact of contrast-enhanced computed tomography (CECT) on routine management of patients with lymphoma. Over a 1-year period, 237 CECT scans were performed prospectively in 163 patients after low-dose (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT). Scans were performed at staging (n = 41), interim (n = 73), post-therapy (n = 115) and follow-up (n = 8). Clinical impact was determined from the multidisciplinary committee reports. CECT had no clinical impact in 219 cases (92%). A clear impact was noted in only 3%, i.e. up-staging of lymphoma (n = 2) and diagnosis of deep vein thrombosis (n = 5). A debatable impact was noted in the remaining 11 cases, consisting of additional investigations, either without therapeutic impact (n = 8), or resulting in delay of therapy onset (n = 2) or ablative surgery (n = 1). CECT delivered an average 33.5 ± 3.8 mSv vs. 17.7 ± 2.8 mSv for PET/CT. In conclusion, the clinical impact of CECT seems limited, although scarce, life-threatening conditions were diagnosed. Imaging of lymphoma needs optimization to reduce radiation exposure.

Metabolic tumour volumes measured at staging in lymphoma: methodological evaluation on phantom experiments and patients.

PURPOSE: The presence of a bulky tumour at staging on CT is an independent prognostic factor in malignant lymphomas. However, its prognostic value is limited in diffuse disease. Total metabolic tumour volume (TMTV) determined on (18)F-FDG PET/CT could give a better evaluation of the total tumour burden and may help patient stratification. Different methods of TMTV measurement established in phantoms simulating lymphoma tumours were investigated and validated in 40 patients with Hodgkin lymphoma and diffuse large B-cell lymphoma. METHODS: Data were processed by two nuclear medicine physicians in Reggio Emilia and Créteil. Nineteen phantoms filled with (18)F-saline were scanned; these comprised spherical or irregular volumes from 0.5 to 650 cm(3) with tumour-to-background ratios from 1.65 to 40. Volumes were measured with different SUVmax thresholds. In patients, TMTV was measured on PET at staging by two methods: volumes of individual lesions were measured using a fixed 41% SUVmax threshold (TMTV41) and a variable visually adjusted SUVmax threshold (TMTVvar). RESULTS: In phantoms, the 41% threshold gave the best concordance between measured and actual volumes. Interobserver agreement was almost perfect. In patients, the agreement between the reviewers for TMTV41 measurement was substantial (ρ c = 0.986, CI 0.97 - 0.99) and the difference between the means was not significant (212 ± 218 cm(3) for Créteil vs. 206 ± 219 cm(3) for Reggio Emilia, P = 0.65). By contrast the agreement was poor for TMTVvar. There was a significant direct correlation between TMTV41 and normalized LDH (r = 0.652, CI 0.42 - 0.8, P <0.001). Higher disease stages and bulky tumour were associated with higher TMTV41, but high TMTV41 could be found in patients with stage 1/2 or nonbulky tumour. CONCLUSION: Measurement of baseline TMTV in lymphoma using a fixed 41% SUVmax threshold is reproducible and correlates with the other parameters for tumour mass evaluation. It should be evaluated in prospective studies.