Volume 15 (2009): Issue 4 (January 2009)

Great names in science represent an inexhaustible source and richness of inspiration, satisfaction and consolation, a moving and victorious force. Throughout her exemplifying life, Maria Sklodowska remained modest but with a keen sense of humor, of an outstanding style, a mine of knowledge and experience, of innovative ideas and a rich inner life. Full of love, of passion to give and to share, of natural optimism, mixed with a light melancholy, so typical for sages. She vehemently defended the love of scientific research, of the spirit of adventure and entrepreneurship and fought for international culture, for the protection of personality and talent. Maria Sklodowska left her passion to science, her dedication to work including education and training of young people, her passionate adherence to her family, her belief in her friends, her pure and profound humanity and warmth!

The paper should be a homage to her, an appreciation of her work over the years, but not less a correspondence, a conversation with her! On the other hand, the present solemn occasion resuscitates the personalities of Maria and Pierre Curie and their work, in particular of Maria Sklodowska in her own native land! In this manner, it truly contributes to her immortality!

Temperature measurement of electrical conductivity s were carried out from 395 to 543 K. The obtained dependence indicates an increase in s. The temperature dependence of the electrical conductivity allowed to observe the release of the free water, bound water and structural water. Studies on electric conductivity of collagen indicate the occurrence of percolation threshold, which comprises free release of water and change its properties from semiconducting to dielectric one.

In this study we describe our experience in implementing compensator based intensity modulated radiotherapy (cIMRT) for head and neck cancer with regard to pre treatment quality assurance (QA), dosimetric parameters and other technical detail.

This study represents the analysis of initial 48 patients who underwent cIMRT for head and neck cancers. All patients were treated with pre treatment QA in terms of point dose with ion chamber and spatial dose comparison with film dosimetry.

In our study for all 48 patients, compensators revealed a deviation in central axis dose of 2% ± 1.8% in terms of cumulative calculated versus measured dose. Target coverage for high dose volume (70 Gy) was adequate in terms of volume receiving 93% and 95% of the prescription dose, which was 98.5% and 97.5% respectively. Parotid and other critical organs were spared adequately. Contralateral parotid (CLP) was spared. V30 Gy and V35 Gy was 55.9% and 36.8% for CLP and average dose was 31.7 Gy. Median variation in cumulative measured dose versus cumulative calculated dose was 1.8% (SD + 1.8) and mean variation was 2.5% (95%CI 1.5, 2.6). Range was 0 to 7%.

cIMRT is practically feasible. Our QA tests revealed high degree of concordance between cumulative measured doses versus cumulative calculated doses. All dosimetric parameters were within acceptable limits. The manufacturing of compensator is cumbersome but it is a one time job followed by easy treatment delivery and simple QA procedure, high monitor unit (MU) efficiency and less treatment time. cIMRT is easy to implement and now can be applied to larger number of patients with different type of tumor.

BNCT facility in the Institute of Atomic Energy in Otwock-Swierk is under construction at the horizontal channel H2 of the research reactor MARIA. Measurements of the neutron energy spectrum performed at the front of the H2 experimental channel, have shown that flux of epithermal neutrons (above 10 keV) at the BNCT irradiation port was below 10⁹ n cm^-2 s^-1 i.e. it was too low to be directly used for the BNCT treatment. Therefore, a fission converter will be placed between the reactor core and the periphery of the graphite reflector of MARIA reactor. The uranium converter will be powered by the densely packed EK-10 fuel elements with 10% enrichment. Preliminary calculations have shown that the total neutron flux in the converter will be about 10¹³ n cm^-2 s^-1 and flux of epithermal neutrons at the entrance to the filter/moderator of the beam will be about 2·10¹³ n cm^-2 s^-1.

This work presents the results of investigation of influence of main exposure parameters on the patient dose and image noise on five clinical computed tomography units. Patient dose was determined by means of the quantity CTDI_air free on air measured with pencil shaped ionization chamber. The image noise was estimated as a standard deviation of CT numbers in a 500 mm² central region of interest in a water-equivalent phantom positioned in the centre of rotation. The alteration of tube voltage and tube current show the potential in patient dose reduction up to 40% but may deteriorate image quality and has to be carefully applied in order to optimize the clinical CT protocols taking into account the specific clinical task. This survey is essential for optimization of routine CT protocols especially for CT units without automatic exposure control systems, which are main part of CT units in Bulgaria.

The aim of this work is to have a preliminary experience with probabilistic tractography. We performed fibres reconstruction for three tracts of interest with data obtained from two MR imaging units equipped with different gradients system. An acquisition protocol optimization has been necessary in order to obtain a good trade-off between image quality and data collection time. Possible solutions to acquisition and processing problems are discussed. Future developments and possible applications in neurosurgery are also suggested.