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1.
Reporting of the clinical relevant dose to organs at risk (OR) and other normal tissues is crucial in trials and protocols where the aim is to assess late complications and to increase the therapeutic ratio for external beam radiotherapy. The dose distribution in normal tissues and ORs are, however, most often heterogeneous, at least when more than two opposing beams are applied. To decide the most clinical relevant dose with respect to late occurring complications is therefore not a straight forward problem. In this work we discuss what parameters characterise the dose-volume-histogram (DVH) best by calculating normal tissue complication probabilities (NTCPs) by using the Lyman model and various sets of statistical parameters drawn out from the DVHs. These NTCPs are compared to NTCPs calculated from the full DVHs, when the sets of parameters are evaluated. Our calculations indicate that the NTCP based on the Lyman model is best correlated to the Dmax value, for serially organised tissues such as the spinal cord. For organs, described largely as tissues organised in parallel, the Dmedian or Dmean of the DVH may be applied. Our calculations reveal that Dmean is the parameter of choice when Dmeclian is quite small, but when the two parameters approach each other, Dmediarl will be a better choice, using a unity volume fraction. For ORs characterised by a mixed serial and parallel functional structure, as the heart, neither Dmax, Dmedian, nor Dmi,an may predict the actual NTCP. 相似文献
2.
Cyclodextrin formulation of dorzolamide and its distribution in the eye after topical administration. 总被引:2,自引:0,他引:2
Hakon H Sigurdsson Einar Stefánsson Elínborg Gudmundsdóttir Thór Eysteinsson Margrét Thorsteinsdóttir Thorsteinn Loftsson 《Journal of controlled release》2005,102(1):255-262
Due to limited aqueous solubility of dorzolamide at physiologic pH, the pH of Trusopt eye drops (cont. 2% dorzolamide) has to be kept at about 5.65, and to increase the topical bioavailability of the drug from Trusopt the contact time of the drug with the eye surface is increased by increasing the viscosity of the eye drops to 100 cps. This low pH and high viscosity can lead to local irritation. In this study, dorzolamide hydrochloride was formulated as 2% and 4% low viscosity solutions (viscosity 3 to 5 cps) containing randomly methylated beta-cyclodextrin at pH 7.45. These formulations were evaluated in rabbits. The animals were sacrificed at various time points after topical administration of the drug and the dorzolamide concentration determined in the different parts of the eye. Trusopt was used as a reference standard. The topical availability of dorzolamide from the cyclodextrin-containing eye drops appeared to be comparable to that from Trusopt and the drug reached retina and optic nerve to give measurable concentrations for at least 8 h after administration of the eye drops. 相似文献
3.
Between 1944 and 1947 the mortality statistics for the Danish population show an epidemic increase of liver diseases: subacute necrosis and cirrhosis. The epidemic only affected female mortality rates. Mortality due to cirrhosis remained at a higher rate for women than men until 1970 as a result of an excess mortality in the cohort of women who in 1945 were over the age of 45. Up to 1981 this group showed an excess of 4,000 fatalities. A reevaluation of medico-statistical data shows that the disease cannot be explained by the epidemic hepatitis occurring in 1942-1944 or by increased consumption of alcohol. Possible causes could be pharmaceutical products or additives, perhaps hormone preparations. 相似文献
4.
Leif Ivar Havelin Nils Roar Gjerdet Ole Dankert Lunde Milan Rait Einar Sudmann 《Acta orthopaedica》1986,57(5):419-422
The wear was examined in 39 Christiansen total hip prostheses, which were removed because of mechanical loosening after being used 5 (3-11) years. In the polyacetal acetabular cups, the head had made an eccentric defect, the mean volume of which was 680 (180-3310) mm3. The mean penetration of the head into the wall of the cup was 0.8 (0.1-3.2) mm. In two additional cups the head had penetrated right through the wall of the cup. In three prostheses the polyacetal sleeve of the trunnion was so worn that the head bore directly on the stem. There was a positive correlation between wear and the time the prostheses had been used before symptoms of loosening presented. 相似文献
5.
Divers' lung function: small airways disease? 总被引:3,自引:0,他引:3
E Thorsen K Segadal B Kambestad A Gulsvik 《British journal of industrial medicine》1990,47(8):519-523
Pulmonary function was measured in 152 professional saturation divers and in a matched control group of 106 subjects. Static lung volumes, dynamic lung volumes and flows, transfer factor for carbon monoxide (T1CO), transfer volume per unit alveolar volume (KCO), delta-N2, and closing volume (CV) were measured and compared with reference values from recent Scandinavian studies, British submariners, and the European Community for Coal and Steel (ECCS) recommended reference values. Diving exposure was assessed as years of diving experience, total number of days in saturation and depth, and as the product of days in saturation and mean depth. Divers had significantly lower values for forced expired volume in one second (FEV1), FEV1/forced vital capacity (FVC) ratio, FEF25-75%, FEF75-85%, FEF50%, FEF75%, T1CO, and KCO compared with the controls and a significantly higher CV. There was a positive correlation between diving exposure and CV, whereas the other variables had negative correlations with diving exposure. Values for the control group were not different from the predictive values of Scandinavian reference studies or British submariners, although the ECCS standard predicted significantly lower values for the lung function variables both in divers and the control group. The pattern of the differences in lung function variables between the divers and controls is consistent with small airways dysfunction and with the transient changes in lung function found immediately after a single saturation dive. The association between reduced pulmonary function and previous diving exposure further indicates the presence of cumulative long term effects of diving on pulmonary function. 相似文献
6.
Ivar Rønnestad Einar Thorsen Kåre Segadal Arvid Hope 《European journal of applied physiology》1994,69(1):32-35
In diving, pulmonary mechanical function is limited by the increased density of the gas breathed. Breathing cold and dry gas may cause an additional increase in airways resistance. We have measured forced vital capacity, forced expired volume in 1 s (FEV1) and forced midexpiratory flow rate (FEF25%–75%) before and after breathing dry or humid gas at 29–32°C during a standardized exercise intensity on a cycle ergometer at an ambient pressure of 3.7 MPa. The atmosphere was a helium and oxygen mixture with a density of 6.8 kg · m–3. Six professional saturation divers aged 26–37 years participated in the study. There were no significant differences in convective respiratory heat loss between the exposures. The mean evaporative heat loss was 67 W (range 59–89) breathing dry gas and 37 W (range 32–43) breathing humid gas, corresponding to water losses of 1.7 g · min–1 (range 1.5–2.2) and 0.9 g · min–1 (range 0.8–1.1), respectively. There was a significant reduction in FEV1 of 4.6 (SD 3.6)% (P<0.05), and in FEF25%–75% of 5.8 (SD 4.7)% (P<0.05) after breathing dry gas. There were no changes after breathing humid gas. By warming and humidifying the gas breathed in deep saturation diving bronchoconstriction may be prevented. 相似文献
7.
8.
Leslie K Jacobsen Kenneth R Pugh Robert T Constable Michael Westerveld W Einar Mencl 《Neuropsychopharmacology》2007,61(1):31-40
BACKGROUND: Cannabis remains the most widely used illicit substance by adolescents and is typically consumed by this population in the context of ongoing tobacco use. Human studies have shown that both cannabis and tobacco exert effects on cognitive function; however, little is known about possible interacting effects of these drugs on brain function and cognition during adolescent development. METHODS: Verbal learning and memory were assessed in 20 adolescent users of tobacco and cannabis and 25 adolescent tobacco users with minimal history of cannabis use. Functional magnetic resonance imaging was used to examine brain function and functional connectivity while a subset of these subjects performed a verbal working memory task. RESULTS: Delayed recall of verbal stimuli deteriorated during nicotine withdrawal among cannabis users but not among comparison subjects. During high verbal working memory load, nicotine withdrawal selectively increased task-related activation of posterior cortical regions and was associated with disruption of frontoparietal connectivity in adolescent cannabis users relative to comparison subjects. CONCLUSIONS: These observations suggest that cannabis use during adolescent development may disrupt neurocircuitry supporting verbal memory formation and that deficits associated with disruption of these neurocircuits are unmasked during nicotine withdrawal. 相似文献
9.
Kjetil G. Brurberg Ilana C. Benjaminsen Liv M.R. Dørum Einar K. Rofstad 《Magnetic resonance in medicine》2007,58(3):473-481
Temporal heterogeneity in blood perfusion is a common phenomenon in tumors, but data characterizing the nature of the blood flow fluctuations are sparse. This study investigated the occurrence of blood flow fluctuations in A-07 melanoma xenografts by using gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced MRI (DCE-MRI). Each tumor was subjected to two DCE-MRI acquisitions separated by 1 hour. The data were processed by Kety analysis and resulted in two E.F images (E is the initial extraction fraction of Gd-DTPA and F is the perfusion) and two lambda images (lambda is the partition coefficient of Gd-DTPA) for each tumor. The E . F images were used to determine the changes in blood perfusion arising in the time between the two imaging sequences. The lambda images were used to control the reproducibility of the experimental procedure. The study showed that DCE-MRI with subsequent Kety analysis is a useful method for detection of blood flow fluctuations in A-07 tumors, and strongly suggested that the peripheral regions of A-07 tumors are more exposed to temporal changes in blood perfusion than are the central regions. 相似文献
10.
Daniel Klase Stefan Gottschalk Erich Reusche Christian Hagel Einar Goebel Volker Tronnier Alf Giese 《Child's nervous system》2007,23(8):907-912
CASE REPORT: The reported female patient underwent sub-total resection of an intra-medullary cervicothoracic astrocytoma classified as WHO grade II in 1984 at the age of 18 months and received local irradiation. In 1989, a local recurrence was diagnosed and a partial resection was performed. Sixteen years later, a small recurrent cervicothoracic tumour was found and spinal seeding to the equine nerve roots and the left cerebellar cortex was apparent on MRI. The patient was implanted with a ventriculoperitoneal shunt for a pseudo-tumour cerebri producing papilloedema, which eventually lead to amaurosis. After an extended biopsy, the invasive lumbosacral tumour was classified as glioblastoma multiforme. Two months later, the patient died after rapid progression of the caudal cranial nerve dysfunction. DISCUSSION AND CONCLUSION: Anaplastic progression and dissemination of spinal astrocytomas even two decades after initial diagnosis and treatment are rare. Therapies and diagnostic follow-up strategies are discussed. 相似文献