Control of accuracy in the Wang-Landau algorithm.

The Wang-Landau (WL) algorithm has been widely used for simulations in many areas of physics. Our analysis of the WL algorithm explains its properties and shows that the difference of the largest eigenvalue of the transition matrix in the energy space from unity can be used to control the accuracy of estimating the density of states. Analytic expressions for the matrix elements are given in the case of the one-dimensional Ising model. The proposed method is further confirmed by numerical results for the one-dimensional and two-dimensional Ising models and also the two-dimensional Potts model.

Interneuronal functional associations in the sensorimotor cortex of dogs.

The interneuronal functional associations were studied in two dogs with Nichrome semi-microelectrodes implanted into the deep layers of the motor and somatosensory regions of the cerebral cortex using the method of cross-correlation analysis. For this purpose the impulse activity of individual neurons was distinguished by form from the background multineuronal activity using the spike recognition technique. Values of a 0.5 and 1 msec-wide bin, and thereafter with a 1 msec step up to 40 msec, were used to plot the cross-interval histograms. The maximal analysis epoch was 2000 msec. The cross-interval associations were monotypal in character; they all presented fairly narrow extrema which were clearly distributed across three time ranges: short-latency associations up to 10 msec; associations with a medium latency up to 80 msec; and associations with late delays, greater than 80 msec. The fairly narrow peak of the association, especially in the case of associations with late delays, was a very difficult phenomenon to explain from the point of view of traditional theoretical perspectives. It is hypothesized that a mechanism exists in the cortex which is responsible for strictly synchronized and highly efficient synaptic transmission.

[The interneuronal functional connections in the sensorimotor cortex of dogs]. / Mezhneironnye funktsional'nye sviazi v sensomotornoi kore u sobak.

Multiunit activity of sensorimotor cortex was recorded from chronically implanted semi-microelectrodes in two dogs. Functional interneuronal connections between neuronal spike trains of 6-8 neurons selected from background multiunit activity were studied by the method of cross-correlation analysis. Bin widths 0.5, 1, 2, 3 and further up to 40 ms by step of 1 ms were used. The cross-interval connections were characterized by complete absence of the shared input (central symmetrical peaks) and signs of inhibitory interrelations. The temporal interrelations between selected neurons were characterized by unilateral and bilateral non-symmetrical excitatory connections--ultra-narrow peaks with short (1-10 ms), middle (10-80 ms) and long (80-2000 ms) delays. The existence of such ultra-narrow peaks contradicts "classical" conceptions on the character of cross-interval connections based on model experiments on simple nervous systems. We suppose that special mechanism of synchronization with high temporal accuracy exists in the cortex.

[Beam radiotherapy of malignant tumors using computer-assisted radiotherapy programs]. / Distantsionnaia luchevaia terapiia zlokachestvennykh opukholei s ispol'zovaniem optimizirovannykh na EBM programm oblucheniia.

The authors give a brief description a ROKUS-M + Altai-MT system, its software ASPECT-1, stages of radiotherapy design and implementation of optimized programs. They gave examples of optimum computerized design of irradiation in tumors of the nasopharynx, breast, female genitals, esophagus, lungs, bladder, and rectum. The paper is illustrated with charts of isodoses and distributions corresponding to optimized programs of irradiation.

[The TDF (time-dose-fractionation) model in brachytherapy]. / Model' VDF pri korotkodistantsionnoi rentgenoterapii.

A method to determine TDF values by standard tables with account of RBE of low-energy x-radiation and a small area of irradiation fields was proposed. Corresponding formulas confirmed by the authors' clinical data, were developed. The authors outlined ways of using these data for assessment and design of courses of brachytherapy to minimize the risk of development of skin radiation damages.

[Application of the DMF model taking into account volume and area of irradiated tissue to the prognosis of radiation complications]. / Primenenie modeli VDF s uchetom ob"ema i ploshchadi obluchaemykh tkanei dlia prognozirovaniia luchevykh oslozhnenii.

Coefficients Kv and Ks for determination of the influence of a volume and area of irradiated tissues in the assessment of DMF factors were presented. The above coefficients were derived on the basis of calculations and a retrospective analysis of the authors' clinical data on radiation complications in the subcutaneous fatty tissue in teleradiotherapy of malignant tumors. The use of the coefficients will make it possible to predict with greater reliability the probability of radiation complications in designing radiation therapy.

[Single large-dose preoperative irradiation in breast cancer]. / Odnokratnoe predoperatsionnoe obluchenie v bol'shoi doze pri rake molochnoi zhelezy.

Proceeding from radiobiological data, the TDF concept and a cumulative radiation effect the authors proposed a new variant of preoperative radiotherapy in operable breast cancer patients. Single doses for the breast and axillary-subclavicular zone that were 15 and 12.5 Gy, were determined. Observation over 72 patients showed that single irradiation did not influence the course of operation and the postoperative period. Good functional and short-term results of treatment make it possible to recommend single large fraction preoperative irradiation for trials in special oncological and radiological institutions.

[Use of time-dose-fractionation models in planning the radiation treatment of malignant tumors]. / Ispol'zovanie modelei vremia-doza-fraktsionirovanie v planirovanii luchevogo lecheniia zlokachestvennykh opukholei.

New methods of the fractionation of preoperative gamma-beam therapy for breast carcinoma and intracavitary irradiation of cervical cancer patients with 252Cf fast neutron sources have been devised and tested on the basis of the concept of a cumulative radiation effect (CRE) and the system of TDF factors at the Chair of Clinical Radiology, Central Institute for Advanced Medical Training. In the selection of regimens of the fractionation of intracavitary irradiation of cervical cancer with 252Cf fast neutrons using the system of TDF factors one should take into account the RBE of the type of radiation that would be equal to 5 by the criterion of a direct response of a tumor within the range of dose rates between 20-30s Gy/hr. Taking account of a short period of half-life of 252Cf sources fractionation schemes should be corrected from the view-point of the system of TDF factors not less than once in 2-3 mos.

[A system of automated radiation treatment of malignant tumors using optimal irradiation programs]. / Primenenie sistemy avtomatizirovannogo luchevogo lecheniia zlokachestvennykh opukholei s ispol'zovaniem optimal'nykh programm oblucheniia.

The authors sum up their clinical experience in the implementation of optimized irradiation programs for tumors of different sites (the esophagus, lung, female genital organs, ear-nose-throat, rectum and urinary bladder) with the help of the first serial specimen of the system of automated control over irradiation--Altai-MT. The utilization of the system makes it possible to save time and avoid an error in the implementation of complex irradiation programs as well as to lower the exposure of medical personnel to radiation. Tumors with average and low radiosensitivity, biologically highly active and located in the vicinity of organs and tissues with a low limit of tolerance to ionising radiation were used as clinical models. Automated programs of irradiation meet the requirements of the conformity and homogeneity of a dose field within a focus of lesion, gradient conditions on the border with normal tissues, the minimization of radiation exposure in critical organs. The purpose of the automation of gamma-beam therapy of tumors is to unite within the common system automated information topometric units and a gamma-therapeutic computer controlled device.