Quality assurance of the dose delivered by small radiation segments

The use of intensity modulation with multiple static fields has been suggested by many authors as a way to achieve highly conformal fields in radiotherapy. However, quality assurance of linear accelerators is generally done only for beam segments of 100 MU or higher, and by measuring beam profiles once the beam has stabilized. We propose a set of measurements to check the stability of dose delivery in small segments, and present measured data from three radiotherapy centres. The dose delivered per monitor unit, MU, was measured for various numbers of MU segments. The field flatness and symmetry were measured using either photographic films that are subsequently scanned by a densitometer, or by using a diode array. We performed the set of measurements at the three radiotherapy centres on a set of five different Philips SL accelerators with energies of 6 MV, 8 MV, 10 MV and 18 MV. The dose per monitor unit over the range of 1 to 100 MU was found to be accurate to within +/-5% of the nominal dose per monitor unit as defined for the delivery of 100 MU for all the energies. For four out of the five accelerators the dose per monitor unit over the same range was even found to be accurate to within +/-2%. The flatness and symmetry were in some cases found to be larger for small segments by a maximum of 9% of the flatness/symmetry for large segments. The result of this study provides the dosimetric evidence that the delivery of small segment doses as top-up fields for beam intensity modulation is feasible. However, it should be stressed that linear accelerators have different characteristics for the delivery of small segments, hence this type of measurement should be performed for each machine before the delivery of small dose segments is approved. In some cases it may be advisable to use a low pulse repetition frequency (PRF) to obtain more accurate dose delivery of small segments.     

A new approach for the calculation of photon dose conversion factors in the PMMA slab phantom

A new simple method using the computer code MCNP is proposed for calculation of photon dose conversion factors in the PMMA slab phantom. Absorbed dose is calculated by multiplying fluence buildup in the PMMA slab phantom by virtual energy deposition in the ICRU tissue substance. This method does not need auxiliary calculations to determine the dose conversion factors, such as calculation of backscatter factors in the ICRU tissue cube and the PMMA slab phantoms. The discrepancies between the results of the direct method presented here and a more conventional indirect method is less than 2%, except for low energy photons (<100 keV) at large depths. As the direct method reduces the number of calculational steps, the results are more reliable than those of the indirect method.     

Quality assurance of brachytherapy by means of interactive computer-assisted planning of the dose distribution using visual optimization (author's transl)

Not earlier than with present generation of afterloading apparatuses,--efficient, reliable and appropriate for many purposes,--it was possible in brachytherapy to give up the previous impractical application techniques. Brachytherapy thus has found the widespread use it merits because of its good results. Additional utilization of a computer for the planning of dose distributions will guarantee the quality possible now in brachytherapy. To that end, a method of computer-assisted planning is described. It can be used for different application techniques. Further improvement of the results obtained till now is discussed in detail.     

Energy and dose rate dependence of a diamond detector in the dosimetry of 4-25 MV photon beams

Motion of the left ventricular cavity center during the cardiac cycle was compared using transthoracic and intracardiac echocardiography. Rotation was comparable for the 2 methods, however, translation of the left ventricular cavity area center was greater with intracardiac echocardiography.     

Training of new coworkers in the intensive care unit as a means for quality assurance

Among patients with bone marrow failure, differentiating acquired aplastic anemia (AA) from hypocellular refractory anemia (hypo RA) can be a difficult and challenging task. Morphological, cytochemical, immunocytochemical, and cytogenetic studies may provide tools for discriminating between both entities. In addition, differences in the pattern of proliferation and apoptosis of bone marrow cells in AA and in the myelodysplastic syndrome have been reported. Because of the correlation between p53 and apoptosis, we examined the overexpression of p53 on bone marrow biopsies in RA and AA. Our study included 14 patients with hypo RA, 14 patients with hypercellular (hyper) RA, ten patients with classic acquired AA, and 37 hematologically normal individuals. p53 was overexpressed in eight (57%) hypo RA patients and 11 (79%) hyper RA patients. All normal individuals and patients with AA showed no overexpression of p53 in their marrow. These results were statistically significant:p < 0.01 (AA vs hypo RA), p<0.001 (AA vs hyper RA), while the difference between hypo RA and hyper RA was not statistically significant. We conclude that p53 overexpression in bone marrow biopsies is a valuable tool for studying bone marrow failure and may provide additional information to help differentiate hypo RA from acquired AA.     

Interfering with the central executive by means of a random interval repetition task

Four dual-task experiments are reported in which a short-term memory task is performed concurrently with a random interval repetition task, which was designed to interfere with functions normally attributed to the central executive in the working memory model of Baddeley and Hitch (1974). The task was found to interfere with supra-span serial recall and with backward memory span, but did not disrupt performance on a forward-memory-span task. The effects were observed in dissociation with effects of articulatory suppression and matrix tapping, so that the locus of the effects of the new task is not due to the slave systems. In addition, single-task random-interval repetition performance was sampled and compared to performance in the dual-task conditions of all four experiments. Although quality of tapping performance differed between the single-task and the dual-task conditions, it was not related to recall performance. All the results are discussed with reference to the working memory model.     

Quality assurance from the viewpoint of medical management by health insurance

Legal requirements of SGB V make provisions for quality assurance (QA) activities in relation to inpatient and outpatient care. Available contracts between health providers and institutions covering costs presently regulate QA in three distinct areas in surgery: inpatient and outpatient care, Fallpauschale (fee for case) and Sonderentgelte (fee for service), and out-patient surgical treatment. MDK as a medical counselling and review agency working on behalf of health insurance companies has a more or less well defined role in the organization (board membership) and actual work (evaluation and probing) of external QA. Its participation and competence derive from legal authorization (SGB V) and hence from its given assignments: review of indication, economical aspects and quality of services provided--each on a single case basis and on a more general basis, nursing care, hospital budgets and finally planning capacity for hospital care.     

A technique for the fast calculation of three-dimensional photon dose distributions using the superposition model

Techniques for reducing computation time in 3D photon dose calculations are addressed with specific emphasis given to the convolution/superposition approach. A single polyenergetic superposition model calculating absorbed dose per incident photon fluence (Gy cm2) was developed in terms of TERMA and a total energy deposition kernel (a total point spread function). A novel approach was devised for reducing calculation time. The method, named the CF method, was based on the use of a conventional, fast model (here a modified power-law method was used) for the generation of 3D dose distributions on a fine dose matrix. Superposition calculations were carried out on a coarse matrix and calculation speed was increased simply by reducing the number of calculations. A set of correction factors was derived on the coarse grid from the ratio of the dose values from superposition to those from the conventional algorithm. These were interpolated onto the fine matrix and used to modify the dose calculation from the conventional algorithm. The method was tested in a worst-case example where large dose gradients were present and in a clinically relevant irradiation geometry. It is shown that the time required for the generation of a 3D matrix with superposition can be reduced by at least a factor of 100 with no significant loss in accuracy.     

Prediction of the lithium ratio in man by means of an in vitro test

The movement of the lithium ion (Li+) across the membrane of intact erythrocytes incubated in vitro was assessed under two different experimental conditions in which such transfer occurred primarily due to the activity of a lithium-sodium countertransport system. The 13 subjects on whom the in vitro procedures were done subsequently received lithium carbonate for 14 to 56 days, and the extent of accumulation of Li+ by erythrocytes in vivo was measured. While both in vitro procedures yielded data that correlated with the extent of accumulation of Li+ by erythrocytes in vivo, a system measuring the efflux of Li+ from Li+-loaded cells produced a much higher correlation (0.976). The magnitude of this correlation suggests that this in vitro system can be used for further investigations into the relevance of the erythrocyte accumulation of Li+ to the pathogenesis and treatment of affective disorders.     

Quality assurance and continuous quality improvement--assessment of the current status of physician self-control for quality assurance in medicine 1955-1995

In April 1996 the working group of the leading statutory health service officials (Arbeitsgemeinschaft der Leitenden Medizinalbeamten der L?nder [AGLMB]) organised a hearing in the course of which the German Medical Association and the National Association of CHI Physicians presented a joint stocktaking of their activities in the discipline of quality assurance during 1955 to 1995. On the basis of this analysis 10 theses have been evolved to develop quality assurance in Germany: (1) quality assurance and quality improvement are in the interest of the medical care of patients. (2) The main task of quality assurance and quality improvement is not the improvement of efficiency. (3) Quality assurance schemes must be problem-orientated and coordinated; there must not be a difference in the quality of out-patient and in-patient medical care. (4) There has to be a systematic evaluation of the suitability of quality assurance schemes. (5) Transparency, communication and cooperation are preconditions for a successful quality assurance and quality improvement. (6) Continuous quality improvement is based on an extensive internal quality assurance. (7) The initiative for the priority development of internal quality assurance procedures must come from external quality assurance. (8) Quality assurance has only a chance of being realised if the individual is convinced and anxious to provide high-quality services, to continuously review and improve his services and to compare them with other services. (9) Quality has its price. (10) Quality assurance and continuous quality improvement are the cornerstones of a quality policy in the health care system. The article concludes with extracts from the checkup and the relevant literature.     

The functional residues and their representation by a hypothetical 3D model of silkworm eclosion hormone

We have previously reported that an insect neuropeptide, eclosion hormone contained an alpha-helix in the N-terminal region and the helix was likely to play an important role in constructing an active globular structure. Furthermore, Met24 and Phe25 were found to be indispensable for the biological activity. On the other hand, no strict structure at the C-terminal side was found. In this paper, we predicted the secondary structure in the C-terminal side and analyzed the functional residues by a Gly-substitution technique. As a result, we speculated that the eclosion hormone contains three alpha-helices throughout the molecule which are essential for an active peptide structure. Moreover, we found four residues important for the biological activity of silkworm eclosion hormone: Phe29, Ile55, Phe58 and Leu59. In order to understand these results stereochemically, we have constructed a 3D structure using computer aided molecular modelling. The hypothetical 3D model showed that Phe25 and Phe58 interact together in a hydrophobic manner to keep a globular form. Met24, Phe29, and Ile55 are exposed to solvent to have a hydrophobic interaction with an eclosion hormone receptor. Leu59 can also play an important role by forming a functional conformation with Phe29 and Ile55.     

New algorithm for analysis of data obtained by means of circular dichroism titration method

Ulcerative lichen planus (ULP) is a rare variant of lichen planus. It is resistant to all therapeutic modalities, and most of the patients with this disorder described in the literature have been successfully treated only by surgical skin grafting. We report a case with ULP successfully treated with etretinate.     

Further evidence for a central role of adipose tissue in the antihyperglycemic effect of metformin

OBJECTIVE: To evaluate further the relative roles played by liver and adipose tissue in the therapeutic response to metformin in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: A total of 11 patients with diet-treated type 2 diabetes were given metformin for approximately 3 months. Measurements were made before and after treatment of 1) fasting and postprandial plasma glucose, insulin, and free fatty acid (FFA) concentrations; 2) glucose appearance (Ra) and disappearance (Rd) rates measured overnight with 3-[3H]glucose; and 3) plasma FFA concentrations during a 195-min infusion period at relatively low insulin (approximately 12-24 microU/ml) concentrations. RESULTS: Mean +/- SEM fasting plasma glucose concentration was significantly lower (175 +/- 11 vs. 224 +/- 15 mg/dl; P < 0.01) after treatment with metformin. Mean +/- SEM insulin concentrations measured from 8:00 A.M. to 5:00 P.M. did not change with treatment. However, both glucose and FFA concentrations were significantly lower (P < 0.01) when measured over the same time period, and the decreases in plasma FFA and glucose concentration were highly correlated (r = 0.81; P = 0.03). Overnight glucose turnover studies indicated that neither Ra (hepatic glucose production [HGP]) nor Rd changed significantly with treatment in association with metformin treatment. Since plasma glucose concentration was much lower after metformin treatment, the overnight glucose metabolic clearance rate (MCR) was significantly lower (P < 0.01). Finally, the ability of insulin to inhibit isoproterenol-stimulated increases in plasma FFA concentration was enhanced in metformin-treated patients (P < 0.05). CONCLUSIONS: Metformin treatment was associated with significantly lower fasting plasma glucose concentrations and lower day-long plasma glucose and FFA concentrations. Although overnight HGP was unchanged after treatment with metformin, the overnight glucose MCR was significantly increased, and the antilipolytic activity of insulin was also enhanced. Given these findings, it is suggested that at least part of the antihyperglycemic effect of metformin is due to a decrease in release of FFA from adipose tissue, leading to lower circulating FFA concentrations and an increase in glucose uptake.     

The detection of chicken meat in meat products by means of the anserine/carnosine ratio

10 patients with their first AMI were studied within the first 48 hours and again after 3 weeks. Central and peripheral haemodynamics (CI, SV, SW, TPR) were examined, including indices of contractility (dp/dtmax) and wall stiffness (deltaP/deltaV, relation deltaP/deltaV to P) of the left ventricle. In the early phase CI and SW, as well as LV dp/dtmax were depressed in accordance with symptoms of LV failure. deltaP/deltaV was increased. Elevation of LVEDP correlated well with ventricular gallop rhythm, but less consistently with LV functional disturbance. During convalescence CI increased uniformly, both in digitalized and non-digitalized individuals. In contrast heart rate, aortic pressure, LVEDP and dp/dtmax remained unchanged. The increase of CI, SV and SW was accompanied by a fall of TPR and deltaP/deltaV. LV wall stiffness was still elevated above normal after 3 weeks. The improvement of cardiac pumping during infarct convalescence may have been effected through a fall of TPR and LV wall stiffness. Recovery of depressed contractile performance was generally not observed, and does therefore not seem to contribute to recuperation.