Dosimetry of ultrasoft x-rays (1.5 keV Al(Kalpha)) using radiochromatic films and colour scanners

This work explores the possibility of measuring the absorbed dose of ultrasoft x-rays (USX, 1.5 keV Al(Kalpha)) with GAFCHROMIC HD-810 radiochromatic dosimetry films (HD-810 films) and colour scanners. HD-810 films were exposed to USX, soft x-rays (14.8 keV) and gamma-rays (60Co) for various times. The response of HD-810 films to absorbed doses of gamma-rays in water was calibrated with Fricke dosimetry and used for the calibration of USX. The optical density of the HD-810 films was quantified with an HP ScanJet 6100C scanner and Corel Picture Paint 7. The choice of the reading channel and colour adjustment settings were optimized to either improve sensitivity or expand the measurable dose range. The response of the HD-810 films to the absorbed dose in water decreased by 50% when the effective photon energy decreased from 1.25 MeV to 14.8 keV. The ratio of the mass energy absorption coefficient of the active layer of HD-810 films to that of water was found to play a major role in this decrease. The mean absorbed doses of the active layer of the HD-810 films exposed to USX were derived. The calculation of the initial photon fluence rate and the mean absorbed doses of USX to biological samples such as plasmid DNA is discussed. This study suggests that radiochromatic dosimetry films are promising secondary dosimeters for measuring the absorbed dose of USX.     

Dosimetry system for the irradiation of thin biological samples with therapeutic proton beams

The design and performance of a dosimetric system for the irradiation of thin biological samples with therapeutic proton beams is reported. Protons with initial energies between 40 MeV and 250 MeV are degraded with polystyrene blocks of variable thickness in order to place the sample, an aqueous layer of 10 microm thickness, at various locations on the proton depth-dose curve. The dosimetric system comprises a secondary emission monitor, a Faraday cup and thin ionization chambers, which are located upstream of the sample, and a calcium fluoride scintillator located downstream of the sample for monitoring the position of the sample relative to the Bragg peak. Transverse dose profiles were measured with radiochromic films. System performance was studied and optimized by simulating primary radiation transport through detectors, degrader and sample using the Monte Carlo simulation tool GEANT 3.21. Calculated detector responses and beam profiles agreed well with the measured data. Monte Carlo simulation was also used to evaluate mean values and spectra of linear energy transfer in the sample as a function of initial proton energy and degrader thickness. Long-term experience has shown that the system performance was unchanged after accumulated doses of 10(5) Gy.     

全身放射治疗的剂量测量研究

目的:在全身放射治疗条件下,测量直线加速器空气中射线场均匀性,水模体内剂量分布情况,以及不同规格水模体的百分深度剂量值。方法:将加速器的源皮距(SSD)延长至450 cm,机架头旋转为90°,准直器开到最大,治疗头旋转为45°,形成菱形射野,使用剂量测量仪:PTW-UNIDOS,电离室:PTW 30001,测量Varian Clinac 2100C直线加速器的剂量值。结果与结论:加速器在空气中射线场剂量:T方向上总的平均值为5.147,绝对误差为5.8%,归一后相对误差达到;G方向上总的平均值为5.124,绝对误差为5.1%,归一后相对误差达到;此加速器的射线场均匀性可以用于全身放射治疗。水模体内剂量分布情况,在10 cm深度处,平均剂量值为8.960,归一数据中的绝对误差为;在20 cm深度处,平均剂量为6.381,从归一数据中的绝对误差为。     

Dosimetry in the space radiation field

Summary The results of dosimetric measurements are presented which were performed as part of a German experiment package flown onboard the Russian space station MIR. These results are compared to those of previous missions: the first United States Spacelab mission and the first German Spacelab mission. Detector packages consisting of plastic nuclear track detectors, nuclear emulsions, and thermoluminescence dosimeters were exposed in different sections of the Russian space station. The equivalent dose for the astronauts was calculated from the measurements to be 3.9 mSv. Before and after the flight venous blood was taken from the astronauts. Chromosomal aberrations in peripheral lymphocytes were analyzed. It was found that the radiation exposure during the spaceflight leads to an elevation of dicentric chromosomes, indicating a radiation burden of the astronauts.Abbreviations D1 first German Spacelab mission - LET linear energy transfer - SL1 first US Spacelab mission - TLD thermoluminescence dosimeter     

Dosimetry of in situ activated dysprosium microspheres

This paper presents the results of a study aimed at investigating the dosimetry of stable dysprosium microspheres activated, in situ, by a linac generated photon beam. In phantom measurements of the neutron flux within an 18 MV photon beam were performed using CR-39 detectors and gold activation. The results were used in conjunction with a Monte Carlo computer simulation to investigate the dose distribution resulting from the activation of dysprosium (Dy) microspheres using an 18 MV photon beam. Different depths, lesion volumes and volume concentrations of microspheres are investigated. The linac lower collimator jaws are assumed completely closed to shield the tumour volume from the photon dose. Using a single AP field with 0 x 0 cm2 field size (closed jaws), a photon dose rate of 600 MU min(-1) and 80 cm SSD for 10 min, an average dose exceeding 1 Gy can be delivered to spherical lesions of 0.5 cm and higher diameter. The variation of the average dose with the size of the lesion reaches saturation for tumour volumes exceeding 1 cm in diameter. This report shows that the photon beam of a high-energy linac can be used to activate Dy microspheres in situ and, as a result, deliver a significant dose of beta radiation. Non-radioactive Dy microspheres do not have the toxicity and imaging problems associated with commercially available yttrium-90 based products.     

Dosimetry of asymmetric x-ray collimators

We have studied the dosimetry of an independent jaw system (provided with the Varian Clinac 2,500) using ionometric measurements performed both in air and in a water phantom. Our study shows that the effect of the independent jaw on the dose distribution is similar to that of secondary blocking except for changes produced in the collimator scatter. A system of dose calculation was developed which takes into account the changes in the collimator scatter as well as in the isodose distribution. A method is described to correctly generate isodose curves for fields shaped by an independent jaw using a modified AECL TP11 treatment planning system. The primary modification in the program consists of correcting the zero-area tissue-maximum ratios for the off-axis variation in beam quality.     

Proton-induced characteristic x-rays: a versatile source of ultrasoft x-rays for biological and biochemical investigations

Very low energy ( ultrasoft ) x-rays of 0.3-5 keV have provided a unique tool for investigation of mechanisms of radiation action, especially with respect to the energy and spatial properties of critical radiation damage in mammalian cells. Experimental investigations to date have been partially limited by the availability and characteristics of suitable ultrasoft x-ray sources. The suitability of small electrostatic proton accelerators, such as exist in many laboratories, have been investigated as a means of producing a secondary beam of ultrasoft x-rays suitable for irradiation of biological and biochemical systems. Results are presented on the physical characteristic of carbon K (0.28 keV) and aluminium K (1.5 keV) ultrasoft x-ray beams produced by bombardment of solid targets of carbon and aluminium with protons of energies up to 750 kV and currents up to 500 microA. These characteristics are compared with those of a cold cathode discharge ultrasoft x-ray tube previously used for mammalian cell investigations. It is seen that the proton accelerator produces much more versatile beams of characteristic ultrasoft x-rays which greatly extend the scope for future experiments on mammalian cells, micro-organisms and biochemical systems. Nevertheless there are situations in which the cold-cathode discharge tube will remain the source of choice and there are other situations, requiring for example energies between characteristic lines, where the greatly more complex synchrotron radiation sources are required.     

Faster identification of mycobacteria using gas liquid and thin layer chromatography

Gas liquid chromatography (GLC) and thin layer chromatography (TLC) analysis of cell wall content was used for identification of mycobacteria isolated in primary cultures. GLC permitted determination of the fatty acid and alcohol profiles ofMycobacterium simiae andMycobacterium marinum and detection of a peak inMycobacterium ulcerans formerly described forMycobacterium malmoense. Using the data obtained to fill some of the gaps in the dichotomic trees of Tisdall et al. and Jantzen et al., GLC analysis allowed full identification of 8 of 22 mycobacterial species after 24 hours. The other 14 species could be divided into four groups on the basis of similar findings on GLC. TLC was used for full identification of three species. The identification results of conventional methods were concordant with those of GLC and TLC in 161 of 169 strains (93 %) representing 21 different species. Using primarily chromatography for analysis of cell wall content, and in the case of some species complementary biochemical tests, the identification procedure could be shortened to a maximum of three days after primary culture.     

Dosimetry comparison of 192Ir sources

192Ir sources besides being widely utilized in the field of conventional brachytherapy also find use in contemporary peripheral and coronal intravascular applications. In this study, the same Monte Carlo simulation code and input data were used to investigate differences between the dose rate distributions of the most commonly used 192Ir sources in the cm and mm distance range. Findings are discussed in view of differences in source and encapsulation dimensions as well as structural details. Results are presented in the AAPM TG-43 formalism, as generalized by AAPM TG-60, for five 192Ir HDR source designs as well as an LDR seed and an LDR wire source. Dose rate constants of the sources at r0 = 1 cm and r0 = 2 mm were found proportional to the corresponding geometry factors along the transverse source bisectors and an equation of the form lambda r0(cGyh(-1) U(-1)) = 1.12 x G(r0,90 degrees) provides results within clinical accuracy (less than 2%) for any 192Ir source. Radial dose functions do not depend significantly on source and encapsulation geometry and agree within 2% with that of a point 192Ir source. Anisotropy is of importance for accurate dosimetry at the cm distance range but it does not affect dose rate in the mm distance range significantly. At such short radial distances the source geometry factor defines the shape of isodose lines. Dose uniformity at given distances from the sources is strongly dependent on source dimensions as indicated by dose rate profiles in polar and Cartesian coordinates.     

Dosimetry of an endocavitory treatment system

The dosimetric properties of an x-ray applicator system for the treatment of rectal carcinoma by endocavitory contact therapy are discussed. Half-value layer, percent depth dose, field flatness, and output dose rate were evaluated. Film was used to evaluate field flatness and ionization chambers were used to evaluate the other quantities. The methods of measurement and their results are discussed.     

Dosimetry study of Re-188 liquid balloon for intravascular brachytherapy using polymer gel dosimeters and laser-beam optical CT scanner

Angioplasty balloons inflated with a solution of the beta-emitter Re-188 have been used for intravascular brachytherapy to prevent restenosis. Coronary stents are in extensive clinical use for the treatment of de novo atherosclerotic stenoses. In this study, the effect of an interposed stent on the dose distribution has been measured for Re-188 balloon sources using the proprietary BANG polymer gel dosimeters and He-Ne laser-beam optical CT scanner. In polymer gels, after ionizing radiation is absorbed, free-radical chain-polymerization of soluble acrylic monomers occurs to form an insoluble polymer. The BANG polymer gel dosimeters used in these measurements allow high resolution, precise, and accurate three-dimensional determination of dosimetry from a given source. Re-188 liquid balloons, with or without an interposed metallic stent, were positioned inside thin walled tubes placed in such a polymer dosimeter to deliver a prescribed dose (e.g., 15 Gy at 0.5 mm). After removing the balloon source, each irradiated sample was mounted in the optical scanner for scanning, utilizing a single compressed He-Ne laser beam and a single photodiode. In the absence of a stent, doses at points along the balloon axis, at radial distance 0.5 mm from the balloon surface and at least 2.5 mm from the balloon ends, are within 90% of the maximum dose. This uniformity of axial dose is independent of the balloon diameter and length. Dose rate and dose uniformity for intravascular brachytherapy with Re-188 balloon are altered by the presence of stent. The dose reduction by the stent is rather constant (13%-15%) at different radial distances. However, dose inhomogeneity caused by the stent decreases rapidly with radial distance.     

Influence of quaternization of ammonium on antibacterial activity and cytocompatibility of thin copolymer layers on titanium

Antimicrobial coatings are able to improve the osseointegration of dental implants. Copolymers are promising materials for such applications due to their combined properties of two different monomers. To investigate the influence of different monomer mixtures, we have been synthesized copolymers of dimethyl (methacryloxyethyl) phosphonate (DMMEP) and dipicolyl aminoethyl methacrylate in different compositions and have them characterized to obtain the r-parameters. Some of the copolymers with different compositions have also been alkylated with 1-bromohexane, resulting in quaternized ammonium groups. The copolymers have been deposited onto titanium surfaces resulting in ultrathin, covalently bound layers. These layers have been characterized by water contact angle measurements and ellipsometry. The influence of quaternary ammonium groups on antibacterial properties and cytocompatibility was studied: Activity against bacteria was tested with a gram positive Staphylococcus aureus strain. Cytocompatibility was tested with a modified LDH assay after 24 and 72 h to investigate adhesion and proliferation of human fibroblast cells on modified surfaces. The copolymer with the highest content of DMMEP showed a good reduction of S. aureus and in the alkylated version a very good reduction of about 95%. On the other hand, poor cytocompatibility is observed. However, our results show that this trend cannot be generalized for this copolymer system.     

Dosimetry of Sr-90 ophthalmic applicators

Sr-90 ophthalmic applicators are commonly used for the treatment of superficial eye disorders. Although a variety of dosimetric devices such as film, thermoluminescent dosimeters (TLD's), ion chambers, and radiochromic foils have been used to measure the peak dose at the applicator surface, there is no internationally agreed upon calibration procedure. Recently, large discrepancies among calibrations of the same applicator at three institutions have been reported. Here we describe a technique to obtain the peak dose rate at the applicator surface using LiF TLD's. The technique can be used for the calibration of flat as well as curved surface applicators. Results for two flat and three concave applicators are presented. Our measurement of the surface dose rate for one of the flat applicators is compared with those obtained by four other institutions, each using different dosimetric devices.     

人工真皮复合自体薄皮移植治疗皮肤软组织缺损

背景：修复皮肤软组织缺损自体或异体植皮治疗,往往需要多次植皮。而国内临床上应用人工真皮较少,应用经验亦不足。 目的：评价人工真皮治疗皮肤软组织缺损的疗效。 方法：收集因皮肤软组织缺损,行人工真皮结合自体薄皮移植修复创面的22例患者,其中骨外露6例,肌腱外露2例,表皮肿瘤切除3例,其他11例。一期清创移植人工真皮,2~4周后局部肉芽组织生长良好,外露肌腱、骨组织被类真皮组织覆盖,二期移植自体薄层皮片。观察取皮部位、损伤部位、操作性能、密封性、不良反应情况,结合评价临床效果及综合评价。 结果与结论：20例患者人工真皮结合二期自体薄皮移植全部存活,至二期植皮所需时间(18.50±4.27) d,其中1例患者因感染再次手术,2例患者行人工真皮后未行二期植皮,而自动上皮化;随访至3个月,21例损伤部位表皮生长性、外观性均良好、无瘢痕增生,1例因感染而致瘢痕增生严重、外观不良,但生长性良好;20例患者取皮部位无明显的色素沉着及色素脱出,无严重增生性瘢痕,上皮形成时间为(15.35±4.67) d。说明人工真皮结合自体薄皮移植修复皮肤软组织缺损,操作简便,创面愈合质量高,供皮区损伤轻微,至二期植皮时间较长,总体临床效果良好。     

Smectic-A liquid single crystal elastomers – strain induced break-down of smectic layers

The mechanical response of a smectic-A liquid-crystalline side-chain polymer network with macroscopically ordered layers (smectic-A liquid single crystal elastomer) to extensive stress applied parallel to the layer normal is described. By stress-strain measurements a characteristic threshold strain of about 3% is observed, at which the elastic modulus changes dramatically. In the regime of small deformation the elastomer remains optically transparent possessing a large Young modulus. The macroscopically ordered smectic-A structure is conserved, probably showing some layer undulation. Above the threshold strain, however, the monodomain structure breaks down and the elastomer becomes completely opaque showing a much smaller elastic modulus. By strain dependent X-ray scattering measurements the structure of the polydomain is analysed. A splitting of the small angle reflection into four maxima is observed, indicating a layer rotation. The intensities of these reflections, however, decrease drastically with strain suggesting a partial distortion of the smectic layers toward a nematic like structure.     

Dual-energy tissue cancellation in mammography with quasi-monochromatic x-rays

Dual-energy radiography has not evolved into a routine clinical examination yet due to intrinsic limitations of both dual-kVp imaging and single-exposure imaging with conventional x-ray sources. The recent introduction of novel quasi-monochromatic x-ray sources and detectors could lead to interesting improvements, especially in mammography where the complex structure of healthy tissues often masks the detectability of lesions. A dual-energy radiography technique based on a tissue cancellation algorithm has been developed for mammography, with the aim of maximizing the low intrinsic contrast of pathologic tissues while being able to minimize or cancel the contrast between glandular and fat tissues. Several images of a plastic test object containing various tissue equivalent inserts were acquired in the energy range 17-36 keV using a quasi-monochromatic x-ray source and a scintillator-coated CCD detector. Images acquired at high and low energies were nonlinearly combined to generate two energy-independent basis images. Suitable linear combinations of these two basis images result in the elimination of the contrast of a given material with respect to another. This makes it possible to selectively cancel certain details in the processed image.