Monte Carlo simulations of the imaging performance of metal plate/phosphor screens used in radiotherapy

The imaging performance of metal plate/phosphor screens which are used for the creation of portal images in radiotherapy is investigated by using Monte Carlo simulations. To this end the modulation transfer function, the noise power spectrum and the detective quantum efficiency [DQE(f)] are calculated for different metals and phosphors and different thicknesses of metal and phosphor for a range of spatial resolutions. The interaction of x-rays with the metal plate/phosphor screen is modeled with the EGS4 electron gamma shower code. Optical transport in the phosphor is modeled by simulating scattering and reabsorption events of individual optical photons. It is shown that metals with a high atomic number perform better than lighter metals in maximizing the DQE(f). It is furthermore shown that the DQE(f) for the metal plate/phosphor screen alone is nearly x-ray quantum absorption limited up to spatial frequencies of 0.4 cycles/mm. In addition, it is argued that the secondary quantum sink of optical photons imposed by the optical chain (mirror, lenses and video camera) leads to a significant degradation of the signal-to-noise ratio at spatial frequencies which are most important for successful registration of portal images. Therefore, the conclusion is that a replacement of the optical chain by a flat array of photodiodes placed directly under the phosphor will lead to a substantial improvement in image quality of portal images.

[Comparison of knee and functional outcomes of patients lost to follow-up with patients remaining in a prospective total knee arthroplasty study]

PURPOSE

Survival analysis is correct when patients lost to follow-up are as healthy as patients still being followed. Therefore, the results of patients who missed the follow-up visits were determined and compared with the results of the patients still in the study. Revision surgery and the reasons for failing to reattend the follow-up visits were recorded.

METHODS

Of 680 unconstrained total knee arthroplasties implanted between 1989 and 1994 with yearly patient evaluation according to the Knee Society 53 patients with 60 implants died, 17 patients with 19 implants could not be used for the study and 21 patients with 24 implants were interviewed by telephone. 56 patients with 61 implants lost to follow-up were examined by visiting them at their homes (drop-outs) and compared to the 460 patients with 516 implants still in the study.

RESULTS

The drop-outs were older at surgery and had more medical infirmity than the remaining patients. Drop-outs had a lower mean function score and a tendency to a lower mean knee score at follow-up compared with the patients in the study. No revision surgery was performed in drop-out knees. Reasons for not reattending the follow-up were mainly long travel and health.

CONCLUSIONS

Patients reattending a study are healthier than drop-outs. This censoring mechanism limits correct survival analysis. A complete follow-up of patients and separate assessment of knee and functional status with reliable and valid instruments is required.

Kawan bronchial brush/cell block technique. Facilitation of the routine diagnosis of bronchial neoplasms

OBJECTIVE

To evaluate cell block preparations as a tool for the diagnosis of pulmonary malignancy and to correlate the findings with those from brush cytology and histology from forceps biopsy.

STUDY DESIGN

One hundred twenty consecutive samples from patients with primary or metastatic lung cancer were routinely processed and stained for cytologic and histologic examination. In addition to smears, a cell block was prepared from each brushing sample. Brush smears, cell blocks and biopsy specimens were compared and evaluated for their diagnostic accuracy.

RESULTS

Brush cytology samples were interpreted as positive for malignancy in all 120 cases. In 42 cases immunohistochemistry performed on cell blocks led to the final precise type diagnosis. Owing to technical problems (stenosis, bleeding, peripheral location), forceps biopsy specimens were obtained from only 51 patients.

CONCLUSION

In addition to lower patient risk, cell block preparation yields high diagnostic accuracy and may thus be considered an improvement in quality assurance.

Multiple fistulas and tracheobronchial stenoses require extensive stenting of the central airways and esophagus in squamous-cell carcinoma

We report here on two cases of double airway and esophageal stenting in patients with multiple esophagotracheal fistulas and stenoses of the airways and esophagus due to squamous-cell carcinoma. Dumon stents and a Strecker device were used for tracheobronchial stenting. Covered Gianturco Z-stents were implanted into the esophagus. In one case, extrinsic compression of the trachea and tumor progression required recanalization by Nd:YAG laser. Clinical improvement led to discharge of the patients within two weeks after the procedure. The results show that simultaneous implantation of stents in the central airways and covered Gianturco Z-stents in the esophagus is an effective therapeutic strategy in patients with tracheal and esophageal obstructions and esophagorespiratory fistulas. Further systematic studies evaluating double stenting are warranted.

Retention of antibacterial activity and bacterial colonization of antiseptic-bonded central venous catheters

We determined how long antiseptic impregnation with silver sulphadiazine and chlorhexidine (SCC) on polyurethane central venous double- or triple-lumen catheters is retained in vivo. A total of 116 antiseptic catheters were tested for antibacterial activity in an in-vitro bioassay after various periods of iv catheterization. Segments from the subcutaneous (sc) and intravenous (iv) portions of the catheters were cultured. The results of test antiseptic catheters were compared with those from 117 noncoated control (c) catheters. Retention of antibacterial activity followed an exponential curve and lasted for up to 520 h after catheter insertion. Significant differences (P = 0.0001) between SSC and C catheters were noticed with regard to the quantitative level of bacterial colonization (SSC-sc 87 +/- 34 vs C-sc 584 +/- 122; SSC-iv 52 +/- 17 vs C-iv 286 +/- 57; all values are given as mean cfu +/- S.E.M.), and the frequency of bacterial colonization (SSC-sc 20.7% vs C-sc 38.5%, P = 0.0047; SSC-iv 18.1% vs C-iv 30.8%, P = 0.0361). There was no significant difference between the incidence of catheter-related bacteraemia in the test (n = 0) and control groups (n = 3) (P = 0.2573). Further prospective studies are required to delineate the role of antiseptic catheters in preventing catheter-related infections.

How much brushing is enough for the diagnosis of lung tumors?

BACKGROUND

Bronchoscopic investigations of lung tumors require high diagnostic accuracy. Sometimes the combination of brush biopsy with cytologic and histologic examination of forceps-obtained biopsy specimens fails to diagnose tumors. Techniques with a minimum risk and low cost when repeated several times could increase the efficiency of tumor diagnosis and help to avoid rebronchoscopy.

METHODS

Repeated brush biopsies were done during one bronchoscopic examination in 270 patients with pulmonary neoplasias using a flexible fiberoptic bronchoscope guided by radiographic video fluoroscopy. The results of up to five brush biopsies were compared for their diagnostic sensitivity.

RESULTS

Singly, 68-77% of the specimens showed malignant findings. With repeated brushing, the sensitivity of the diagnostic accuracy increased to 89.6%. In the periphery of the bronchial tree, the sensitivity of brush biopsy was slightly lower in bronchoscopically invisible tumors. In 222 of 242 (91.7%) patients with positive results of brush biopsy, there was agreement in the final typing of tumor morphology.

CONCLUSION

For routine bronchoscopy, repeated brush biopsy should be done to obtain the highest diagnostic yield.

[Acinar cell carcinoma of the salivary glands]

Between 1972 and 1985, eleven cases of acinic cell carcinoma were treated at the ENT clinic of the University Hospital Geneva. Eight of them were located in the parotid gland, three in minor salivary glands, two of these on the hard palate and one on the lower lip. Local recurrence occurred in four cases: two were recurrences of a parotid gland carcinoma and two of a minor salivary gland carcinoma. Three patients developed metastases, two in cervical lymph nodes and one in the lungs. Two tumours presented a very aggressive local development. Hence, the acinic cell carcinoma has a significant tendency to recur, to produce metastases, and may have an aggressive evolution. Radical treatment by surgery is necessary.

Proteolytic activity of Candida albicans and other yeasts

Clinical isolates of C. albicans (75 strains) and other yeasts (20 strains) were evaluated for their ability to produce a carboxyl acid proteinase in an effort to assess its potential role as a virulence factor. Yeasts were categorized as to the infectious process present in the patient: (1) isolates from patients with invasive disease, (2) isolates from patients with possible invasive disease, (3) isolates from superficially infected patients and (4) isolates from noninfected, colonized patients. Yeasts were grown for 7 days in medium containing bovine serum albumin (BSA) as the sole nitrogen source. The amount of extracellular proteinase was measured at pH 3.2, using BSA as substrate. The majority (97%) of C. albicans isolates produced a detectable proteinase. Some non-C. albicans isolates produced proteinase; however, the amount of activity was generally less than for C. albicans. No correlation was found between the amount of proteolytic activity and the degree of invasiveness of the strains.

Long-term results of prosthetic ureteral replacement in minipigs

In a 3-year study, silicone rubber prostheses were implanted in 6 minipigs as ureteric replacement. A Dacron velour cuff was applied for the proximal anastomosis and a disc of the same material implanted into the bladder wall to anchor the prosthesis distally. The silicone tube incorporated a metal spiral to prevent kinking. On autopsy all anastomoses were firm and resistant to tearing except in 1 animal where the proximal end of the prosthesis had loosened without further complications. Incrustation or leakage never occurred. On histology dense ingrowth of collagen fibres into the meshes of Dacron velour was evident. Malignant cells could never be demonstrated. The findings are compared with a previous 12-month study. The growth of polypoid structures occluding the prosthesis was found to be a new problem with long-term alloplastic ureteric replacement. The best results were achieved with unilateral prostheses after contralateral nephrectomy.

Protection of mice against 7,12-dimethylbenz(a)anthracene-induced skin tumors by immunization with a fluorinated analog of the carcinogen

5-Fluoro-12-methylbenzanthryl-7-acetic acid (5-FMBAAA) is an analog of the carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) with little or no carcinogenic activity. CD-1 mice immunized with 5-FMBAAA conjugated to bovine serum albumin (BSA) developed serum antibodies capable of binding DMBA. As a means of testing whether this immunization protected against DMBA-induced tumors, a low-dose carcinogenesis model system was developed, entailing the repeated skin application of 25 ng DMBA in dodecane alternating with applications of the tumor promoter, phorbol myristate acetate. Mice immunized with the 5-FMBAAA:BSA conjugate and subsequently exposed to this low-dose regimen for 40 weeks developed significantly fewer skin tumors (0.23 papilloma/mouse) than did unimmunized mice, mice immunized with BSA, or mice immunized with an unconjugated mixture of BSA and 5-FMBAAA (0.47 to 0.54 papilloma/mouse). Immunization did not reduce tumor incidence in mice treated with phorbol myristate acetate alone. The results suggest that, when mice are exposed to a carcinogen at doses low enough to approach environmental levels, immunization against the carcinogen can provide specific protection.

Behaviour of the different oxidation states of As, Sb, Se an Sn using dithiocarbamates for their separation from environmental, food and drug samples

The mentioned elements are known to occur in the environment in different oxydation states with different biological activities. Speciation of the oxydation state by selective enrichment can lead to relevant information for the toxicologist. A sample treatment procedure is described that --allows to discriminate between the oxidation states of the mentioned elements --converts the elements to the optimum oxydation state for enrichment from the sample --brings the elements in an ideal form for their determination by x-ray fluorescence analysis using coprecipitation with the dibenzyl-ammoniumsalt of dibenzyldithiocarbamic acid. An outline of the method, instrumentation used and applications to organic, biological and environmental samples is given.

Formation of adherent monolayers of murine lymphocytes in vitro: the use of serum-free medium and concanavalin A-coated surfaces to promote adherence

Murine thymus and spleen cells formed adherent monolayers in polystyrene tissue culture flasks when plated in serum-free medium. In the presence of 2% serum, thymus cells adhered poorly, but adherence was greatly enhanced if the flasks had been coated noncovalently with the lectin, concanavalin A. Adherence of leukemic lymphocytes (L1210) required both serum-free medium and concanavalin A-coated flasks; the extent of attachment was proportional to the concentration of the lectin used to coat the flasks at concentrations up to 0.1 mg/ml. Once L1210 cells had attached, they could not be removed by exposure to serum, ethylenediamine tetraacetic acid, trypsin, or alpha-methyl mannoside. Adherent L1210 cells remained capable of metabolism and proliferation during intervals of up to 7 days. The use of adherent monolayers for cytotoxicity assays was demonstrated by an assay for Pseudomonas aeruginosa toxin in EL4 murine leukemia cells.