Assessment of radionuclide impurities in [18F]fluoromethylcholine ([18F]FMCH).

PURPOSE: [18F]Fluoromethylcholine ([18F]FMCH) is a radiopharmaceutical used in positron emission tomography (PET) imaging for the study of prostate, breast, and brain tumors. It is usually synthesized in cyclotron facilities where 18F is produced by proton irradiation of [18O]H2O through 18O(p,n)18F reaction. Due to the activation of target materials, the bombardment causes unwanted radionuclidic impurities in [18O]H2O, that need to be removed during the radiopharmaceutical synthesis. Thus, the aim of this study is to quantify the radionuclide impurities in the 18F production process and in the synthesized [18F]FMCH, demonstrating the radionuclidic purity of this radiopharmaceutical. METHODS: Long-lived radionuclide impurities were experimentally assessed using high-resolution gamma and liquid scintillation spectrometries, while short-lived impurities were monitored analyzing the decay curve of the irradiated [18O]H2O with an activity calibrator. As spectrometric radionuclide library, a Geant4 Monte Carlo simulation of the 18F-target assembly was previously performed. RESULTS: 3H, 52,54Mn, 56,57,58Co, 95m,96Tc, 109Cd, and 184Re were found in the irradiated [18O]H2O, but no radionuclide was found in the non-irradiated [18O]H2O neither in the final [18F]FMCH solution with an activity concentration greater than the minimum detectable activity concentration. A total impurity activity <6.2 kBq was measured in the irradiated [18O]H2O, whereas a [18F]FMCH radionuclide purity >99.9999998% was estimated. Finally, the decay curve of the irradiated [18O]H2O revealed a very low maximum of 13N activity (<0.03% of 18F) even immediately after the end of bombardment. CONCLUSIONS: This study demonstrated the radionuclidic purity of [18F]FMCH according to the EU Pharmacopeia.

Evaluation of equivalent dose to eye lens through dose equivalent Hp(3).

PURPOSE: Individual dosimetry allows to quantify doses from ionizing radiation of exposed workers. Scientific and epidemiological evidences highlight the need for adequate measures for a greater protection of the eye and a reduction in annual doses. ICRP Publication 103, illustrating the operational dose quantity Hp(d) for the individual monitoring, proposes a depth d = 3 mm for eye lens monitoring, indicating that even the Hp(0.07) can be used. In this study, it was investigated if there are differences in the evaluation of the equivalent dose to eye lens (Hlens) using Hp(3) or Hp(0.07). MATERIALS AND METHODS: A slab phantom calibration was performed by an Accredited Calibration Laboratory in terms of Hp(3) and Hp(0.07) using ext-rad TLD-100 (LiF:Mg,Ti) dosimeters. Hp(0.07) and Hp(3) were measured for 26 exposed workers to assess Hlens. The measuring took place monthly in 2017 to obtain both semestral and annual doses. RESULTS: Hlens(0.07) was always smaller than Hlens(3). However, the differences were not statistically significant (Mann-Whitney test, p > 0.05) for both semestral and annual doses. The percentage differences were 7 ±â€¯3%, 6 ±â€¯3% and 7 ±â€¯2% for I semester, II semester and whole year, respectively. The mean underestimation index <10%, intra-class correlation coefficient >0.99, coefficient of variation <3% and the excellent correlation (R2 ≈ 0.999) for both semestral and annual doses highlighted that Hp(0.07) can be used to evaluate Hlens instead of Hp(3). CONCLUSIONS: No statistical evidence was found that the use of Hp(0.07) underestimates the equivalent dose to eye lens obtained through Hp(3).

Short-course versus split-course radiotherapy in metastatic spinal cord compression: results of a phase III, randomized, multicenter trial.

PURPOSE: Hypofractionated radiotherapy (RT) is often used in the treatment of metastatic spinal cord compression (MSCC). This randomized trial was planned to assess the clinical outcome and toxicity of two different hypofractionated RT regimens in MSCC. PATIENTS AND METHODS: Three hundred patients with MSCC were randomly assigned to a short-course RT (8 Gy x 2 days) or to a split-course RT (5 Gy x 3; 3 Gy x 5). Only patients with a short life expectancy entered the protocol. Median follow-up was 33 months (range, 4 to 61 months). RESULTS: A total of 276 (92%) patients were assessable; 142 (51%) treated with the short-course and 134 (49%) treated with the split-course RT regimen. There was no significant difference in response, duration of response, survival, or toxicity found between the two arms. When short- versus split-course regimens were compared, after RT 56% and 59% patients had back pain relief, 68% and 71% were able to walk, and 90% and 89% had good bladder function, respectively. Median survival was 4 months and median duration of improvement was 3.5 months for both arms. Toxicity was equally distributed between the two arms: grade 3 esophagitis or pharyngitis was registered in four patients (1.5%), grade 3 diarrhea occurred in four patients (1.5%), and grade 3 vomiting or nausea occurred in 10 patients (6%). Late toxicity was never recorded. CONCLUSION: Both hypofractionated RT schedules adopted were effective and had acceptable toxicity. However, considering the advantages of the short-course regimen in terms of patient convenience and machine time, it could become the RT regimen of choice in the clinical practice for MSCC patients.