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In this study, the total mass attenuation coefficients (μ(m)) for some homo- and hetero-chain polymers, namely polyamide-6 (PA-6), poly-methyl methacrylate (PMMA), low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) were measured at 59.5, 511, 661.6, 1173.2, 1274.5 and 1332.5 keV photon energies. The samples were separately irradiated with (241)Am, (22)Na, (137)Cs and (60)Co (638 kBq) radioactive gamma sources. The measurements were made by performing transmission experiments with a 2″×2″ NaI(Tl) scintillation detector having an energy resolution of 7 % at 662 keV gamma ray from the decay of (137)Cs. The effective atomic numbers (Z(eff)) and the effective electron densities (N(eff)) were determined experimentally and theoretically using the obtained μ(m) values for the investigated samples. Furthermore, Z(eff) and N(eff) of each polymer were computed for total photon interaction cross-sections using theoretical data over a wide energy region from 1 keV to 10 MeV. The experimental values of the selected polymers were found to be in good agreement with the theoretical values.

The mass attenuation coefficients (μs) for five different soil samples were measured at 661.6, 1173.2 and 1332.5 keV photon energies. The soil samples were separately irradiated with 137Cs and 60Co (370 kBq) radioactive point gamma sources. The measurements were made by performing transmission experiments with a 2″ × 2″ NaI(Tl) scintillation detector, which had an energy resolution of 7% at 0.662 MeV for the gamma-rays from the decay of 137Cs. The effective atomic numbers (Zeff) and the effective electron densities (Neff) were determined experimentally and theoretically using the obtained μs values for the soil samples. Furthermore, the Zeff and Neff values of the soil samples were computed for the total photon interaction cross-sections using theoretical data over a wide energy region ranging from 1 keV to 15 MeV. The experimental values of the soils were found to be in good agreement with the theoretical values. Sandy loam and sandy clay loam soils demonstrated poor photon energy absorption characteristics. However, clay loam and clay soils had good photon energy absorption characteristics.

RESULTSThe mean follow-up was 23.0±19.4 months and the median overall survival was 39 months (95% CI, 12.6-65.4 months), with one-and two-year survival rates of 71% and 45%, respectively. Imaging follow-up using RECIST at three-month intervals demonstrated partial response in 43%, complete remission in 3%, stable disease in 37%, and progressive disease in 17% of patients. Extent of tumor involvement was found to have a statistically significant influence on overall survival (P = 0.03). The existence of extrahepatic disease at the time of radioembolization, radiographic response, age, and primary neuroendocrine tumor site were not significant prognostic factors. CONCLUSIONThe current study demonstrates the effectiveness and safety of radioembolization for the treatment of unresectable NETLMs. We identified that the extent of tumor involvement has a significant effect on overall survival. The use of imaging methods reflecting metabolic activity or cellularity such as scintigraphy or diffusion-weighted MRI would be more appropriate, for the response evaluation of liver metastases after radioembolization. N euroendocrine tumors (NETs) are a heterogenous group of slow-growing and hormon-releasing malignant tumors. Even though primary NETs originate from a number of locations, 40%-70% of all carcinoids arise in the small intestine and appendix (1, 2). The most common site for metastasis is the liver. Neuroendocrine tumor liver metastasis (NETLM) results in hormone-secretion-related symptoms leading to carcinoid syndrome, pressure on structures, or liver replacement (1-4). Patients with liver metastasis have a five-year survival rate of less than 20% (5). Over the years, improvements in local treatments yielded better control of the symptoms and survival rates, yet only 10% of the patients have limited illness and are eligible for surgery (6). Patient symptomatology and survival can be improved by transarterial treatments like embolization and chemoembolization (6). Limitations of these techniques include the short duration of the effects and the controversial approaches regarding the optimal timing and sequence of the procedures due to the variability of tumor progression (7,8). Long-term survival benefit was not achieved with systemic chemotherapy (9-11) and treatment with somatostatin analogues is mostly associated with symptomatic relief; there is no clear knowledge of their effect on survival of patients who have carcinoid tumor and metastasis (12).Selective internal radiation therapy (SIRT) has been used to treat unresectable primary and secondary liver cancers for over a decade.

The treatment of patients with PMC should be no different from the treatment of patients with PTC, and thyroidectomy followed by radioiodine therapy may be a possible option for treatment of papillary microcarcinoma.

In the present work, different methods were used to determine the effective atomic numbers of some low-Zmaterials, namely, polyethylene (PE), polystyrene (PS), polypropylene (PP), Perspex (PX), polycarbonate (PC), nylon 6-6 (PA-6), plaster of Paris (POP), and TH/L2. These methods are the direct method, the interpolation method, Auto-Zeffsoftware, and single value XMuDat computer program. Some of the results obtained were compared with experimental data wherever possible. It can be concluded from this work that the effective atomic numbers calculated with the direct, the interpolation and Auto-Zeffmethods demonstrate a good agreement in Compton scattering and pair production energy regions. A large difference in the effective atomic numbers calculated by the direct and the interpolation methods of low-Zmaterials was also observed in photoelectric and pair production regions. It was determined that PE, PS, PX, and PA-6 were equivalent to adipose and muscle; POP was equivalent to cortical bone; TH/L2 was equivalent to thyroid tissue; PP was equivalent to yellow bone marrow and adipose tissues; PC was equivalent to spongiosa.

Background/aim: To describe the role of baseline gallium (Ga)-68 DOTATATE positron emission tomography (PET)/computed tomography (CT) in the prediction of the response to peptide receptor radionuclide therapy (PRRT) using lutetium (Lu)-177 DOTATATE.Materials and methods: Analysis was made of baseline Ga-68 DOTATATE PET/CT images of 29 patients (17 females and 12 males; mean age: 50.7 ± 14.6 years) with metastatic neuroendocrine tumors who received PRRT with Lu-177 DOTATATE. Maximum standardized uptake values (SUVmax) of reference lesions and their ratios to physiological uptake organs were calculated. The relationship between these values and the radiological response was analyzed.Results: Partial response was observed in 8 (28%) patients, stable disease in 18 (62%) patients, and progressive disease in 3 (10%) patients. Mean SUVmax of reference lesions was calculated as 23.8 ± 20.5 (min-max: 5.1-87.3). There was no significant correlation between radiological responses and SUVmax of reference lesions and their ratios to other organs. Conclusion:Baseline Ga-68 DOTATATE PET/CT helps to show somatostatin receptor expression status and disease stage in patients who are candidates for PRRT. However, SUVs do not have a role in the prediction of treatment response.