Determination of Effective Spectrum of Medical Linear Electron Accelerators from Depth Dose Distributions

 Development of the spectrum reconstruction method for bremsstrahlung beams with different field sizes, created medical electron linear accelerators (LAE), on the base of the deep dose distributions in a water phantom and determination of photon spectra for Varian Trilogy accelerator 6 MV. The proposed methodology is based on the use of dose kernels algorithm of point monoenergetic monodirectional source (pencil beam (PB)) for the depth dose distribution calculation, created different cross-section beams of in a water phantom, and experimental measurements of these distributions. For solving the inverse problem is applied Toolbox routines ’Optimtool’ knowing mathematical package MATLAB to solve. Bremsstrahlung energy spectrum generated medical accelerator Varian Triology with different sizes of square fields from 3 x 3 up to 40 x 40 cm2 and average energy photons, depending on the size of the fields were received. Dose kernels for a set of defined energies PB were calculated. Depth dose distribution in a water phantom, calculated using the obtained spectra and dose kernels agree well with measurement dose distributions. The proposed technique reconstruction of bremsstrahlung spectrum of medical accelerator is good adequate. Average energy spectra of photons for Varian Trilogy Accelerator in regime 6 MV varies from 1.71 to 1.43 MeV depending on the field size. Keywords: radiation therapy, medical accelerators, bremsstrahlung, reconstruction of the photon spectrum

Determination of Small Beam Axial Dose Distribution in Water Based on the Mathematical Model of Pencil Beam Kernels

An analytical model of the dose kernel of pencil beam for photon with the Bremsstrahlung spectrum with maximum energy 6 MV was created in this work, which makes it possible to determine the primary and scattered components of the absorbed dose in water phantom with an acceptable error for practice. Using this model a simply method of dosimetry of small circular cross section 6 MV photon beam was proposed. It combines the absolute measurement of the absorbed dose in the water at the reference point for reference geometry with the calculation of the deep dose distribution by simple analytical formulas for circular beams with an arbitrary radius of the cross section. Keywords: dose kernels, pencil beam, dosimetry, small photon beam, radiotherapy

Secondary Electron Spectral Changes of Irradiated Gold Nanoparticle Caused By PEGylation

Gold nanoparticles attract attention for the use in radiation therapy of tumors due to the ability to enhance the efficacy of ionizing radiation. The magnitude of the radiosensitizing effect depends on the parameters of the nanoparticle, in particular on the modification of the surface. In the present work, the spectrum of secondary particles generated in a gold nanoparticle virtually irradiated with 60Со gamma rays as a result of surface modification by a polyethylene glycol shell was studied. The Mont eCarlo calculations revealed that modification of the nanoparticle’s surface changes the spectrum of secondary particles. The most robust was the loss in low-energy electrons (51%) whereas the yield of Compton electrons increased by 1.27 times. At the same time, no statistically significant changes were observed in the spectrum of secondary photons and photoelectrons. Simulation of the formation and distribution of secondary electron radiation makes it possible to evaluate the parameters important for the rational design of antitumor nanoradiosensitizers based on chemical elements with a high atomic number. Keywords: gold nanoparticles, radiosensitizers, Monte-Carlo simulation, Geant4, radiation therapy, malignant tumors

DIAGNOSTICS AND TREATMENT OF RECURRENT POSTOPERATIVE GOITER

The study developed the system of therapeutic and prophylactic methods in patients with recurrent postoperative goiter. These patients (103) have been accepted and registered in the medical records since 2007. Only 48 patients underwent recurrent operation. The subtotal resection of the thyroid gland was performed on 20 patients and thyroidectomy was carried out in 28 patients. The perioperative visualization of recurrent laryngeal nerves was made in 58,3% cases. Postoperative period was complicated by unilateral recurrent nerve trauma in one patient and transient hypoparathyroidism was noted in two patients. The recurrent operative interventions must be performed in specialized centers and it should be extremely radical operation with visualization of recurrent laryngeal nerves

Influence of the microorganisms’ metabolites from West and East Siberia permafrost on proliferative activity of human lymphocytes in vitro

Исследовано влияние метаболитов 14 штаммов микроорганизмов (МО), выделенных из многолетнемерзлых пород (ММП) Западной (район Тарко-Сале) и Восточной (Чарская котловина Читинской области) Сибири и Центральной Якутии (Мамонтова гора), на пролиферативную активность лимфоцитов периферической крови (0(I)Rh+)) в реакции бласттрансформации (РБТЛ). Учитывалось число бласттрансформированных лимфоцитов в спонтанном варианте РБТЛ (с-РБТЛ); под влиянием митогена для Т-лимфоцитов фитогемагглютинина (ФГА); метаболитов МО из ММП; комплекса «ФГА+метаболиты». Установлено, что разные штаммы МО из ММП могут оказывать как стимулирующее, так и супрессивное влияние на пролиферацию лимфоцитов. Максимальное стимулирующее влияние оказал штамм F2 из ММП Центральной Якутии (p<0,01), минимальное – штаммы 9/48(II) и 5/26 из ММП Западной Сибири (p<0,05). Штамм F2 также способствовал увеличению уровня пролиферации лимфоцитов в комплексе с ФГА (p<0,05). Достоверно снижают стимулированную ФГА пролиферацию лимфоцитов 2 штамма из ММП Западной Сибири – 9/48(II) и 3/07 (p<0,01 в обоих случаях) и 2 штамма из ММП Восточной Сибири – 6/010 и 2/09 (p<0,01 в обоих случаях).The effect of metabolites of 14 strains of the microorganisms isolated from the permafrost of West (near Tarko-Sale) and Eastern (Chara depression Chita Oblast) Siberia and Central Yakutia (Mamontova mountain) on the proliferative activity of peripheral blood lymphocytes (0(I)Rh+)) in the reaction of blast-cell transformation. The authors consider the number of blast-cell transformed lymphocytes in the spontaneous blast-cell transformation under the influence of mitogen for T-lymphocytes of phytohemagglutinin (PHA) and under microbial metabolites of permafrost of PHA + metabolites complex. It is found that different strains of the permafrost microorganisms can have both stimulatory and suppressive effect on lymphocyte proliferation. The strain F2 from Central Yakutia permafrost is exerting maximum stimulating effect (p<0.01), minimum – strains 9/48 (II) and 5/26 from Western Siberia permafrost (p <0.05). Strain F2 is increasing the level of lymphocyte proliferation in combination with PHA (p<0.05). Two strains of Western Siberia permafrost – 9/48 (II) and 3/07 (p<0.01 in both cases) and two strains of Eastern Siberia permafrost – 6/010 and 2/09 (p<0.01 in both cases) are significantly reducing PHA-stimulated lymphocyte proliferation

Radiosensitization by Gold Nanoparticles: Impact of the Size, Dose Rate, and Photon Energy

Gold nanoparticles (GNPs) emerged as promising antitumor radiosensitizers. However, the complex dependence of GNPs radiosensitization on the irradiation conditions remains unclear. In the present study, we investigated the impacts of the dose rate and photon energy on damage of the pBR322 plasmid DNA exposed to X-rays in the presence of 12 nm, 15 nm, 21 nm, and 26 nm GNPs. The greatest radiosensitization was observed for 26 nm GNPs. The sensitizer enhancement ratio (SER) 2.74 &plusmn; 0.61 was observed at 200 kVp with 2.4 mg/mL GNPs. Reduction of X-ray tube voltage to 150 and 100 kVp led to a smaller effect. We demonstrate for the first time that the change of the dose rate differentially influences on radiosensitization by GNPs of various sizes. For 12 nm, an increase in the dose rate from 0.2 to 2.1 Gy/min led to a ~1.13-fold increase in radiosensitization. No differences in the effect of 15 nm GNPs was found within the 0.85&ndash;2.1 Gy/min range. For 21 nm and 26 nm GNPs, an enhanced radiosensitization was observed along with the decreased dose rate from 2.1 to 0.2 Gy/min. Thus, GNPs are an effective tool for increasing the efficacy of orthovoltage X-ray exposure. However, careful selection of irradiation conditions is a key prerequisite for optimal radiosensitization efficacy

Impact of the Spectral Composition of Kilovoltage X-rays on High-Z Nanoparticle-Assisted Dose Enhancement

Nanoparticles (NPs) with a high atomic number (Z) are promising radiosensitizers for cancer therapy. However, the dependence of their efficacy on irradiation conditions is still unclear. In the present work, 11 different metal and metal oxide NPs (from Cu (ZCu = 29) to Bi2O3 (ZBi = 83)) were studied in terms of their ability to enhance the absorbed dose in combination with 237 X-ray spectra generated at a 30–300 kVp voltage using various filtration systems and anode materials. Among the studied high-Z NP materials, gold was the absolute leader by a dose enhancement factor (DEF; up to 2.51), while HfO2 and Ta2O5 were the most versatile because of the largest high-DEF region in coordinates U (voltage) and Eeff (effective energy). Several impacts of the X-ray spectral composition have been noted, as follows: (1) there are radiation sources that correspond to extremely low DEFs for all of the studied NPs, (2) NPs with a lower Z in some cases can equal or overcome by the DEF value the high-Z NPs, and (3) the change in the X-ray spectrum caused by a beam passing through the matter can significantly affect the DEF. All of these findings indicate the important role of carefully planning radiation exposure in the presence of high-Z NPs