Central Shield Research Articles

High-dose-rate intracavitary brachytherapy (HDR-IC) in treatment of cervical carcinoma: 5-year results and implication of increased low-grade rectal complication on initiation of an HDR-IC fractionation scheme

Purpose : To report the treatment results and rectal/bladder complications of cervival carcinoma radically treated with high-dose-rate intracavitary brachytherapy (HDR-IC). The current policty of using three-fraction scheme was examined. Methods and Materials : Between November 1987 and August 1990, 173 patients with cervical carcinoma were treated with curative-intent radiation therapy. Whole pelvic irradiation was administered with 10-MV X ray. Dose to the central cervix was 40–44 Gy in 20–22 fractions, following by pelvic wall boost 6–14 Gy in three to seven fractions with central shielding. 60Co sources were used for HDR-IC, and 7.2 Gy was given to Point A for three applications, 1–2 weeks apart. Duration of follow-up was 5–7.8 years. Results : Twenty-eight patients (16%) developed central-regional recurrences. Overall 5-year actuarial pelvic control rate was 83%. By stage, 5-year actuarial pelvic control rates were 94%, 87%, and 72% for Stages IB + IIA, IIB + IIIA, and IIIB + IVA, respectively. Thirty-one patients (18%) developed distant metastasis. Overall 5-year actuarial survival rate was 58%. By stage, 5-year actuarial survival rates were 79%, 59%, and 41% for Stages IB + IIA, IIB + IIIA, and IIIB + IVA, respectively. Sixty-six (38%) and 19 patients (11%) developed rectal and bladder complications, respectively. For rectal complication, the overall actuarial rate was 38% at 5 years. By grade, 5-year actuarial rectal complication rates were 24%, 15%, 4%, and 3% for GRades 1–4, respectively. Overall prevalence of rectal complications was 37% and 14% at 2 and 5 years, respectively. Prevalence of low-grade rectal complication (Grades 1 and 2) was dominant at 2 years (30%), but declined to 8% at 5 years. Prevalence of high-grade, severe rectal complication (Grade 3 and 4) remained steady at 2 and 5 years (7% and 6%, respectively). Five-year actuarial bladder complication was 9%. Five-year prevalence of bladder complication was 2%. Conclusion : Using a three-fraction scheme, survival rate appeared comparable with the existing results of the low-dose-rate technique. The incidence of rectal complication with this scheme remained relatively high. The increased part of rectal complication was predominantly low grade. This result suggested that therapeutic gain with this scheme may not be good enough to circumvent its biologic disadvantage. Number of fractions > 3 must be considered in future trials.

155 Cervix carcinoma: Treatment and results

In 1984 we treated 391 patients with cervix carcinoma of all stages (FIGO: st. I—108, st. II—144, st. III—136 and st. IV 3) using Cathetron (HDR Co-60) for brachytherapy and Linear accelerator (10 MeV) for external beam therapy. The treatment regimen were: Cathetron: (a) radical irradiation—4 × 1000 cGY/.A. 1 fraction/week, (b) irradiation after surgery—4 × 750 cGy/0.5 cm, 1 fraction/week. Linear accelerator: (a) radical irradiation—4600 cGy, 22 fractions, 2 opposite fields with central lead shields after 2000 cGy, (b) irradiation after surgery—3600 cGy, 18 fractions, 2 opposite field without central shields. The 5-year survival of patients was: st. I—89/108 (82.4%), st. II—104/144 (72.2%), st. III—55/136 (40.4%), st. IV—0/3 (0.0%) and all stages—248/391 (63.4%). Late post-irradiation sequelae were: 41/391 (10.5%). Local recurrences were: 35/391 (9.0%). Distant metastases: 6.75%.

Ring currents and magnetisability in C 60

A distributed-origin coupled Hartree-Fock method is used to compute the current density induced in C 60 by an external magnetic field, and hence to plot the π ring currents and obtain ab initio values of the total magnetisability and nuclear magnetic shielding. Paramagnetic ring currents are associated with pentagons, and interpreted as consequences of strong, local circulations about the formal double bonds of the C 60 framework. The calculated total magnetisability of −370 cgs ppm is strongly diamagnetic and in agreement with the previous extrapolated ab initio result and with an experimental measurement. The calculated central shielding of +12 ppm is in qualitative agreement with the previous extrapolation and the measured encapsulation shift for 3He in C 60. It is concluded that C 60 is diagmagnetic, but that the interpretation of this diamagnetism as a sing of three-dimensional aromaticity is problematic.

Heat flow and thermal structure of the lithosphere across the Baltic Shield and northern Tornquist Zone

Terrestrial heat-flow data from Archean and Proterozoic Provinces of the Baltic Shield, its southwestern margin, and the tectonic transition to the younger tectonic units of Central Europe (northern segment of the European Geotraverse) are compiled and examined for local and regional variations. A 2-D numerical lithospheric temperature and heat-flux model is presented covering 1800 km of the deep seismic Fennolora profile across the Baltic Shield and 500 km of Eugeno-s/ northern Eugemi seismic lines across the northern Tornquist Zone and the Danish and North German basins. Thermal lithosphere, defined as the outer layer with relatively low temperatures ( T < 1200–1400° C) in which heat transfer is dominantly by conduction, is found to vary markedly in thickness from 85–110 km beneath basins and Tornquist Zone to about 150 km in central shield areas, and 200–250 km in areas of low heat flow along the northern shield profile. These results are in very good agreement with seismological information from surface wave dispersion analysis and the refraction / wide-angle seismic interpretation of Fennolora data. The combined thermal and seismologic evidence indicates that the uppermost mantle region stratified in seismic velocity is restricted to the upper, relatively cold thermal layer, which is interpreted to constitute shield lithosphere. Local and to some extent regional variations in surface heat flow are found to be closely related to variations in near-surface radiogenic heat production. For the southern Baltic Shield a heat-flow / heat-production relationship of q 0 = 32.8 + 7.6 H 0 is derived. Regional increase in heat flow from northern and central shield provinces to the shield margin and the Tornquist Zone is interpreted to be related partly to differences in upper-crustal heat generation, partly, and in southernmost areas mainly, to an increased heat flux from the upper mantle. Upper-mantle heat flux is estimated at 20–25 mW m −2 along the northern and central shield transect, increasing to 30–40 mW m −2 beneath the shield margin, basins, and Tornquist Zone. Lithospheric thickness variations in this region of northern Europe are found to be closely associated with variations in heat flux from the uppermost mantle and perhaps to a large extent controlled by geodynamically determined lateral differences in upper-mantle heat flux. Earthquake focal depth data and information on crustal strength show Baltic Shield seismicity to be limited generally to the upper 20–25 km brittle part of the crust at temperatures less than 300–400°C. Maximum source depth of magnetic anomalies at temperatures near 600°C is in the deepest part of the crust near the crust-mantle boundary in the southern region (about 25 km depth along the Tornquist Zone and about 35–40 km in southern shield areas) and in the uppermost mantle (60–70 km depth) in the northern shield areas. Some petrologic implications are discussed. The present deep crust is supposed to be at lower temperature-pressure conditions than at early stages of formation. However, also the present deepest parts of the shield crust (> 35–40 km) are within the stability field of eclogites. The general absence of significant gravity anomalies in areas of marked crustal thickness variations indicate high-density eclogites to be present in significant amounts in the deep shield crust.

The role of lymphangiography in designing fields for elective pelvic node irradiation in Hodgkin's disease

Purpose: We attempted to design a standard pelvic nodal treatment field such that all lymph nodes usually visualized on lymphangiogram would be irradiated with optimal midline blocking of normal tissues. Methods and Materials: Two standard fields for treatment of pelvic lymph nodes were designed, based on bony landmarks. The standard fields were applied to the anterior-posterior view of 35 pretherapy lymphangiograms, and the fields were then assessed for inclusion of visible lymph nodes. Measurements were done on the lymphangiograms to assess the amount of additional midline blocking that could be added. Results: All visualized nodes were included in 30 patients (86%) using Standard Field I and in 33 patients (94%) using Standard Field 11, but visualized nodes plus a 1.5-cm minimum margin were included in only two patients (6%) with Field I and 24 patients (69%) with Field 11. The most frequent sites of close margins were the lateral and medial borders adjacent to the external iliac nodes. Based on the lymphangiograms, a mean of 1.6 cm in male patients and 3.1 cm in female patients could be added to the width of the midline blocks. Conclusion: Lymph angiography is useful in designing fields for pelvic node irradiation, both to improve coverage of nodes with a 1.5 cm margin and to increase the amount of central shielding of normal tissues.

Dosimetry of centrally shielded electron beams

In electron beams, the dose in phantom under the central shielding depends on electron-beam energy, depth in phantom, and shield area and thickness. In our experiments, all shield thicknesses were larger than the range of electrons in the shield material. At a given depth, the dose under the shield never exceeds the open field value; however, it can attain quite a large proportion of the open field value despite a shield thickness which exceeds the range of electrons in the shield material. The effects of shield area on the dose under the central shields were studied in detail and dose distributions are given as a function of shield lateral dimensions and electron-beam energy. It is shown that in clinical use of central shielding, the best approach to dose estimation under the shield is direct measurement in phantom under conditions of the actual clinical setup.

Regional Rock Quality Designation (RRQD) of the West Central Arabian Shield

Engineering and hydrogeological behaviors of rock masses are intimately related to the intensity, extension and orientation of discontinuities hosted by the rock. Qualitative descriptions of such discontinuities provides general base information about any type of engineering structure such as dams, highways, pressure tunnels, airports, etc. However, more significantly, their quantitative descriptions are of prime importance especially concerning design variables. One of the most used indices in this regard is the Rock Quality Designation (RQD). So far in the literature only one-dimensional assessments of RQD are available along scanlines such as tunnel axis or along highway rock cuttings. This paper extends the concept of RQD into two dimensions which helps to assess the rock quality on a regional basis. The technique proposed herein is based on lying a regular mesh over the study area and calculating the regional RRQD values at nodal points by considering two orthogonal directions along which conventional RQD9s are obtained. Based on these nodal points contour maps or three-dimensional appearances of RQD within the region are presented.

Crustal helium fluxes and heat flow in the Great Artesian Basin, Australia

New measurements of the He concentration in bore waters from the Great Artesian Basin (Australia) show: (1) a regional increase in the 4He flux over the Central Shield, where high heat flow has been attributed to increased U, Th and K in the crust; and (2) a reduced 4He flux and enhanced 3He flux in eastern Australia, where high heat flow is attributed to volcanism or underplating during the Cenozoic. These observations suggest correlations between (1) the crustal 4He flux and the component of heat flow attributed to crustal U and Th (and K), as well as (2) the 3He flux and recent volcanic activity. However, the specific relations between the heat flux and the He flux can be considerably modified by transport processes and source fractionation. It is suggested that time-dependent tectonic models of heat and mass (He) transport in the crust may be used to constrain either the components of heat flow or the bulk rate of mass transport in the Earth's crust.

In-situ sputtering of YBCO films for microwave applications

RF magnetron sputtering from a single YBCO target onto a heated substrate ( approximately=700 degrees C) was used to obtain c-axis-oriented 1-2-3 films that are superconducting without a subsequent annealing or oxygenation step, with T/sub c/(R=0) as high as 88 K on MgO and LaAlO/sub 3/ substrates. This process uses an 8-in-diameter target in the sputter-up configuration, with a central grounded shield to eliminate negative ion bombardment. It can reproducibly and uniformly cover substrates as large as 3-in across at rates exceeding 1 AA/s. Maintaining film composition very close to stoichiometry is essential for obtaining films with good superconducting properties and surface morphology. Optimum films have critical currents of approximately=1 MA/cm/sup 2/ at 77 K. Measurements of microwave surface resistance based on a stripline resonator indicate low surface resistance for unpatterned YBCO ground planes, but excess loss and a strong power dependence in a patterned center strip.

Simuliidae (Diptera: Culicomorpha) in Brazil. X. Description of Simulium (Psaroniocompsa) guaporense sp.n

É descrita uma nova espécie para o subgênero Simulium (Psaroniocompsa) Enderlein: S. (P.) guaporense proveniente da Província Hidrogeológica do Escudo Central, pertencente ao grupo "siolii" (S. siolii, S. lourencoi, S. damascenoi) descrito por Py-Daniel (1988).

Geology and petrogenesis of lavas from San Cristobal Island, Galapagos Archipelago

Volcanism became emergent on San Cristobal Island 2.3 m.y. B.P. in the eruption of floods of alkaline basalt. Volcanism then coalesced in a central shield volcano, which erupted continually until 0.6 m.y. B.P. At 0.9 m.y. B.P., activity began to jump to the northeast, and the style of volcanism changed to fissure-fed eruptions that have continued almost to historical time. Three distinct magma series occur on San Cristobal: an alkaline series, a series of MORB-like tholeiites, and a series of incompatible-element–enriched tholeiites that are typical of oceanic islands. Each series is represented by very primitive basalts that have been little modified since segregation from their sources. Each series also has more-evolved lavas, which range from low-Mg basalts to hawaiites and icelandites. These evolved lavas are the result of simple fractional crystallization of magmas which produces major- and compatible-element compositions similar to those of observed primitive lavas. The isotope and trace-element data suggest that the different series are generated by different degrees of partial melting and mixing of both a depleted and an enriched source. The first source is thought to be the depleted asthenosphere which generates the MORB9s of the Galapagos Spreading Center, and the enriched source is the mantle plume associated with the Galapagos hotspot.

Stratigraphy and palaeogeography of the Siham group:direct evidence for a late Proterozoic continental microplate and active continental margin in the Saudi Arabian Shield

The presence of ancient continental crust in the Afif terrane of the Arabian Shield has been indicated by radiometric data. Detailed mapping in the central Shield reveals a volcano-sedimentary succession older than one of the final cratonizing events of the Shield and unconformable upon high grade paragneisses, providing direct evidence for a western continental margin to the Afif terrane in late Proterozoic times. The basement gneisses were metamorphosed to almandine-sillimanite amphibolite facies and preserve evidence of a deformation not seen in any other rocks of the area. The Siham group, unconformable upon this basement, was metamorphosed to upper greenschist facies. It has been divided into six formations which provide an E–W section through the group. The lower members are volcanic and are absent in the easternmost formation. Their clastic content increases eastward. A carbonaceous shale with exhalative chert and marble, tuffs and associated volcanogenic massive sulphides is associated with the volcanics. It is absent in the east where shallow marine marbles and quartzites lie unconformably upon basement. Rhyolite and conglomerate complete the succession. In the west, the base of the group is not seen but the shale is associated with numerous sheet-like bodies of mafic and ultramafic rock emplaced in an extensional tectonic setting. Other plutonic rocks are calc-alkaline and are emplaced mainly in the west. Deep water oceanic conditions prevailed in the west and a shallow marine continental shelf environment existed in the east, with deposition of the group across this continental margin. The stratigraphy of the Siham group is particularly akin to the Mesozoic of Peru. Magmatic arc and marginal basin were coincident in space and time, and the marginal basin was probably extensional. There is some limited evldence that it was ensialic. The Siham group is bounded to the west by a N-S suture zone formed in one of the final collisional events in the cratonization of the Shield. This event caused the deformation of the Siham group and marked the termination of the magmatic are.

The structural evolution of the Tibchi ring-complex: a case study for the Nigerian Younger Granite Province

In the Tibchi Complex, an initial gas build-up in the ascending felsic magma was most probably accompanied by updoming of the overlying basement rocks. Paroxysmal volcanic eruptions followed and culminated in a central shield volcano whose conduit was eventually sealed. Magmatic activity was renewed, with consequent increase in magma pressure but the volcano's load effect hindered a new central updoming or reopening of the already welded volcanic neck. Instead there resulted a peripheral stress concentration around the volcano to form a master cone-fracture that was apparently complete as a ring-fracture and which in attitude was inward-dipping at depth, steepening towards the ground surface. Fluidization along the ring-fracture brought about surface cauldron subsidence of the early volcanic edifice, and intra-caldera extrusion of crystal-rich ignimbrites. Fluidization waned as the magma became depleted in gas; the feeders to the crystal-rich ignimbrites were frozen in the ring-fracture as quartz porphyries. Gas-poor magma corresponding to the present granite porphyry ring-dyke displaced the frozen quartz porphyries by ring-fracture stoping and marked the transition to the plutonic phase of intrusion.

Stereo X ray photogrammetry applied for prevention of sigmoid-colon damage caused by radiation from intrauterine sources

Radiation therapy of cervix carcinoma is applied in this Institute by means of a modified Stockholm method in combination with external beam irradiation. In 1968, parametrial portals were replaced by large planparallel opposed fields extending cranially to LIII/LIV with central shielding in order to avoid overdosage in the area of intracavitary treatment. This resulted in a marked increased incidence of severe sigmoid-colon radiation lesions from 0.25% to 4%; predominantly in Stage I and It patients. Therefore two measures have been introduced: beginning in 1972 measures were taken to prevent the cranial displacement of the uterus during intracavitary treatment in order to shortening the distance between the radioactive sources and the sigmoid-colon; from 1973 stereo X ray photogrammetry (SRM) was applied for dose determinations at points of the sigmoid-colon, which were seen to be located close to the applicator. When SRM data indicated that a high dose at the sigmoid-colon might occur, treatment modifications enabled prevention of radiation damage. Change of position of the applicator was the first to be considered. In the last seven years no surgical intervention had to be performed because of a sigmoid-colon lesion resulting from an unexpected high radiation dose delivered by intrauterine sources. The local recurrence rate was not increased following treatment modifications for prevention of sigmoid-colon radiation damage.

Preliminary correlations of MAGSAT anomalies with tectonic features of Africa

An overview of the MAGSAT scalar anomaly map for Africa has suggested a correlation of MAGSAT anomalies with major crustal blocks of uplift or depression and different degrees of regional metamorphism. The strongest MAGSAT anomalies in Africa are closely correlated spatially with major tectonic features. Although a magnetic anomaly caused by a rectangular crustal block would be offset from the block's center by the effects of magnetic inclination, an anomaly caused by real crustal blocks of varying uplift, depression, and degree of regional metamorphism would be located nearer to the locus of greatest vertical movement and highest grade of metamorphism. Thus, the Bangui anomaly may be caused by a central old Precambrian shield, flanked to the north and south by two relatively young sedimentary basins.

An investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the United States in the 0.5-4 Hz band

Summary. Studies of teleseismic P-and S-wave amplitudes and spectra in the 0.5–4 Hz band show large variations in the attenuative properties of the upper mantle under the United States. The data indicate that attenuation is greatest under the south-western United States including, but not confined to, the Basin and Range province. The lowest attenuation prevails under the north central shield regions. The north-eastern part of the country, consisting of New England and possibly including a larger area along the eastern seaboard, is characterized by moderate attenuation in the mantle. The level of the high-frequency energy in short-period seismic waves and the differences between Q values derived from short-and long-period data indicate that Q is frequency dependent. The form of frequency dependence of t* compatible with the data in the 0.5–4 Hz range does not allow a rapid decrease of t* with increasing frequency. Rather it supports a gradual decrease covering the broader 0.1–4 Hz range. The curves of t* versus frequency, for shield-to-shield and mixed shield-to-western United States type paths are parallel with an average difference of 0.2 s in t* in the short-period band, but may diverge towards the long-period band. For both curves t*p is below 1 s. For shield-to-shield paths t*p must be below 0.5 s at 1 Hz.

Petrochemistry of lavas from the Central Arabian shield

Petrochemistry of lavas from the Central Arabian shield

Antimony-121 nuclear magnetic resonance study of hexahaloantimonate anions

The seven hexahaloantimonate anions in the series [SbClnBr6−n]− have been prepared and their antimony-121 nmr spectra show that for [SbCl4Br2]−, [SbCl3Br3]−, and [SbCl2Br4]−, only the cis isomers are present in acetonitrile solution. The pairwise additivity model for central atom shielding has been used for configuration assignments. Models relevant to the higher incidence of cis over trans isomers are discussed. The nuclear shielding of 121Sb is the most sensitive to halogen substitution of all the elements whose halide chemical shifts have been studied. Antimony shieldings exhibit normal halogen dependence, with bromine substitution causing upfield shifts relative to chlorine substitution.

The quaternary uplift of the rhenish shield in germany

Abstract The Rhenish shield in Central Europe is made up by a series of slates, quartzites and limestones of dominantly Devonian age which were strongly folded by the Hercynian orogeny. The area has been uplifted to about 300 m since the Pliocene. Rates of uplift increased during the last 600,000 years as shown in the uplifted terraces of the Rhine river. The drainage pattern was forced to erode deep antecedent river valleys in the uplifted plateau. Two late Quaternary volcanic fields have developed on the Rhenish shield: The West Eifel, covering an area of some 500–600 km2 with c. 220 eruptive centers; and, about 25 km to the east, the smaller East Eifel (Laacher See area) with some 70 volcanic centers distributed over c. 400 km2. Magmas of both fields are moderately potassic. Most West Eifel magmas are nephelinites and leucitites and have high CaO/Al2O3-ratios (up to about 1.45) and 87 86 Sr-ratios (0.7039–0.7044); in contrast, intermediate (tephritic) and highly differentiated (phonolitic) magmas are common in the East Eifel, where magma chambers of different compositions have developed at varying depths in the crust, as evidenced by a variety of crustal xenoliths. Primitive East Eifel magmas are dominantly basanites with Mg numbers 87 86 Sr-ratios (0.7041–0.7047). The Quaternary Eifel magmas must have come from a different mantle area than the Tertiary magmas, whose 87 86 Sr-ratio ranges from 0.7035–0.7040. Most of the existing seismic-refraction profiles in the Rhenish shield have been reinterpreted using travel time and amplitude information. The general pattern of observed phases can be divided into three types: (1)Throughout the central shield a strong P-phase reflection from the crust—mantle boundary is recorded. The average crustal thickness is 28–29 km and the average crustal velocity is 6.2–6.3 km/sec. (2)Beneath the southern part of the shield strongly reflected phases show clear intracrustal and Moho discontinuities. Along profiles crossing major volcanic features the Mdiscontinuity is disrupted and an intermediate intracrustal boundary at about 20 km depth forms the main reflector. Beneath this boundary the velocity increases gradually from about 7 km/sec to upper-mantle velocities. (3)For profiles crossing the northern Rhinegraben area as well as for a line east of the Lower Rhine embayment, the observed phases indicate only one major seismic boundary at a depth of about 23 km where the velocity increases to 7.3 km/sec. Below this boundary the velocity increases gradually with depth reaching 8 km/sec at 27–28 km. The Rhenish shield is part of an incoherent block mosaic of the Alpine foreland. The Alps are under rapid Holocene uplift and sideward extension. Between the Alps and the Rhenish shield there is a major foreland block which is shifted northwestward to be sheared along the Rhinegraben rift with a sinistral polarity. The northern apex of this block wedges in the Rhenish shield and provokes an axial deformation and, conditioned by that, a split-up of the northwestward frame of the shield. It is shown that the shield uplift evolved as a consequence of horizontal deformations of the unit. Subcrustal rift propagation under the tectonically incompetent crustal unit of the Rhenish shield had favored magmatic activity, thermal rise and subsequent plateau uplift.

An Axi-Symmetric High Flux Muon Channel

This paper reports the results of a design study of an axi-symmetric high flux muon channel which consists of three coaxial coils. A primary beam strikes a thick production target located on the axis near the midplane of the first coil. Annular slits are located between the first and second coil to define the range of take-off angles relative to the axis and the momentum range of the secondary particles that are accepted. The accepted particles spiral in the axial magnetic field and return to the axis to strike a degrader located near the midplane of the second coil. The muon beam leaving the degrader has its momentum range separated from the momentum range of the electrons and pions leaving the degrader. Annular slits are placed between the second and third coils to transmit the muons and stop the pions and electrons. A beam spot suitable for experiments with stopping muons is produced downstream of the third coil. A central shielding plug and a spiral baffle stop neutrons and secondary particles of the opposite sign. Such a system will have a peak solid angle of acceptance off the production target ? l sr and will accept a momentum range > ± 3%. With a suitably chosen degrader material, the channel can alternatively produce a pure pion beam. A fourth coil can be included in the channel to produce a volume of uniform field suitable for the operation of a time projection chamber.