Clinical dosimetry using MOSFETs

PURPOSE

The use of metal oxide-silicon field effect transistors (MOSFETs) as clinical dosimeters is demonstrated for a number of patients with targets at different clinical sites.

METHODS AND MATERIALS

Commercially available MOSFETs were characterized for energy response, angular dependency of response, and effect of accumulated dose on sensitivity and some inherent properties of MOSFETs. The doses determined both by thermoluminescence dosimetry (TLD) and MOSFETs in clinical situation were evaluated and compared to expected doses determined by calculation.

RESULTS

It was observed that a standard calibration of 0.01 Gy/mV gave MOSFET determined doses which agreed with expected doses to within 5% at the 95% confidence limit for photon beams from 6 to 25 MV and electron beams from 5 to 14 MeV. An energy-dependent variation in response of up to 28% was observed between two orientations of a MOSFET. The MOSFET doses compared very well with the doses estimated by TLDs, and the patients tolerated MOSFETs very well. A standard deviation of 3.9% between expected dose and MOSFET determined dose was observed, while for TLDs the standard deviation was 5.1%. The advantages and disadvantages of using MOSFETs for clinical dosimetry are discussed in detail.

CONCLUSION

It was concluded that MOSFETs can be used as clinical dosimeters and can be a good alternative to TLDs. However, they have limitations under certain clinical situations.

Reversible focal ischemia in the rat: effects of halothane, isoflurane, and methohexital anesthesia

Barbiturates and the volatile anesthetic isoflurane reduce CMR to similar values. If the mechanism of barbiturate protection against focal ischemic injury is due to a reduction in cellular energy requirements, then isoflurane should similarly reduce ischemic injury. To evaluate this, spontaneously hypertensive rats underwent 2 h of reversible middle cerebral artery occlusion (MCAO) while receiving deep methohexital, isoflurane, or halothane anesthesia. Ninety-six hours postischemia, neurologic deficits were present but without a difference between groups. Mean +/- SD infarct volume, as assessed by triphenyl tetrazolium chloride staining and computerized planimetry, was significantly less in the methohexital group (n = 8; 166 +/- 74 mm3) than in either the halothane (n = 9; 249 +/- 71 mm3; p less than 0.04) or the isoflurane (n = 9; 243 +/- 62 mm3; p less than 0.03) groups. One possible explanation for the lack of protective effect for isoflurane might be related to its vasodilative properties, which could result in a cerebral vascular steal. To examine this possibility, rats anesthetized with methohexital or isoflurane underwent autoradiographic determination of CBF with or without MCAO. In isoflurane-anesthetized sham rats (n = 5; no ischemia), CBF was approximately three times greater than in methohexital-treated (n = 5) sham rats. During ischemia, although a regional reduction in flow was noted in both anesthetic groups, mean flow remained greater in the isoflurane group.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of API 20C and ID 32C systems for identification of common and rare clinical yeast isolates

The abilities of the API 20C and ID 32C yeast identification systems to identify 123 common and 120 rare clinical yeast isolates were compared. API 20C facilitated correct identification of 97% common and 88% rare isolates while ID 32C facilitated correct identification of 92% common and 85% rare isolates.

The use of radiochromic film in treatment verification of dynamic stereotactic radiosurgery

Standard silver-based films are usually too sensitive to be used as direct indicators of dose in dynamic radiosurgery because of optical saturation. This paper describes the use of a new radiochromic film to measure 6-MV radiosurgery doses and dose distributions in a head phantom. Dose calibration of the radiochromic film was performed in the range of 2.3-50.2 Gy using light of 632- and 530-nm wavelengths. Radiosurgery dose distributions were measured using the radiochromic film in a head phantom undergoing the same treatment as a patient, and were compared with the planned distributions. For an example case (nominal 2.0-cm-diam cone), film measurement verified the calculated dose distribution in one plane. The simple measurement technique described led to experimental uncertainties of +/- 0.1 cm for the 90% and 50% isodose lines, +/- 0.3 cm for the 20% line, and +/- 0.5 cm for the 10% line. Isocenter dose was measured with an uncertainty of +/- 3%. Refinements to the technique should allow more precise measurements. It is concluded that the radiochromic film, with some limitations, is a convenient and useful tool for dynamic radiosurgery quality assurance.

Flow cytometry antifungal susceptibility testing of pathogenic yeasts other than Candida albicans and comparison with the NCCLS broth microdilution test

Candida species other than Candida albicans frequently cause nosocomial infections in immunocompromised patients. Some of these pathogens have either variable susceptibility patterns or intrinsic resistance against common azoles. The availability of a rapid and reproducible susceptibility-testing method is likely to help in the selection of an appropriate regimen for therapy. A flow cytometry (FC) method was used in the present study for susceptibility testing of Candida glabrata, Candida guilliermondii, Candida krusei, Candida lusitaniae, Candida parapsilosis, Candida tropicalis, and Cryptococcus neoformans based on accumulation of the DNA binding dye propidium iodide (PI). The results were compared with MIC results obtained for amphotericin B and fluconazole using the NCCLS broth microdilution method (M27-A). For FC, the yeast inoculum was prepared spectrophotometrically, the drugs were diluted in either RPMI 1640 or yeast nitrogen base containing 1% dextrose, and yeast samples and drug dilutions were incubated with amphotericin B and fluconazole, respectively, for 4 to 6 h. Sodium deoxycholate and PI were added at the end of incubation, and fluorescence was measured with a FACScan flow cytometer (Becton Dickinson). The lowest drug concentration that showed a 50% increase in mean channel fluorescence compared to that of the growth control was designated the MIC. All tests were repeated once. The MICs obtained by FC for all yeast isolates except C. lusitaniae were in very good agreement (within 1 dilution) of the results of the NCCLS broth microdilution method. Paired t test values were not statistically significant (P = 0.377 for amphotericin B; P = 0.383 for fluconazole). Exceptionally, C. lusitaniae isolates showed higher MICs (2 dilutions or more) than in the corresponding NCCLS broth microdilution method for amphotericin B. Overall, FC antifungal susceptibility testing provided rapid, reproducible results that were statistically comparable to those obtained with the NCCLS method.

Rapid flow cytometric susceptibility testing of Candida albicans

A rapid flow cytometric assay for in vitro antifungal drug susceptibility testing was developed by adapting the proposed reference method for broth macrodilution testing of yeasts. Membrane permeability changes caused by the antifungal agent were measured by flow cytometry using propidium iodide, a nucleic acid-binding fluorochrome largely excluded by the intact cell membrane. We determined the in vitro susceptibility of 31 Candida albicans isolates and two quality control strains (Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258) to amphotericin B and fluconazole. Amphotericin B MICs ranged from 0.03 to 2.0 microg/ml, while fluconazole MICs ranged from 0.125 to 128 microg/ml. This method results in clear-cut endpoints that were reproducible. Four-hour incubation was required for fluconazole, whereas a 2-h incubation was sufficient for amphotericin B to provide MICs comparable to the reference macrodilution method developed by the National Committee for Clinical Laboratory Standards Subcommittee on Antifungal Susceptibility Tests. Results of these studies show that flow cytometry provides a rapid and sensitive in vitro method for antifungal susceptibility testing of C. albicans.

Molds in onychomycosis

BACKGROUND

Onychomycosis is a major cause of nail dystrophy. The causative organisms in onychomycosis are dermatophytes, Candida and molds. A variety of molds have been isolated from nails.

METHODS

Nail scrapings and clippings were collected from 100 cases and inoculated on slants containing SDA with cycloheximide 0.5 mg/mL, chloramphenicol 0.05 mg/mL, and SDA with chloramphenicol 0.05 mg/mL.

RESULTS

The culture positivity rate for molds was 22%. The predominant mold isolates were Aspergillus species (86.4%, Fusarium oxysporum (4.5%), Curvularia species (4.5%) and Penicillium species (4.5%).

CONCLUSION

Primary invasion of nails by molds can cause onychomycosis.

A Dose–Response Study of the Influence of Propofol on Cerebral Blood Flow, Metabolism and the Electroencephalogram in the Rabbit

This experiment was designed to study the effect of progressively increasing blood propofol concentrations on cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), and the electroencephalogram (EEG). Nine New Zealand White rabbits were anesthetized with morphine (10 mg kg bolus and 2 mg/kg/h infusion) and 70% N2O. Both normothermia and normocarbia were maintained throughout the study. A 300 mum diameter platinum electrode and a 20 gauge sampling needle were inserted into the confluence of venous sinuses to permit the measurement of forebrain CBF and CMRO2. Cerebral blood flow was determined using the H2 clearance method and CMRO2 was calculated as CBF x arteriovenous O2 content difference. A single bifrontal EEG signal was also recorded. After baseline data were collected, a propofol infusion was begun, and the dose increased in a stepwise fashion from 0.28 to 1.11 mg/kg/min over 90 min (total dose 62.6 mg/kg). Every 22.5 min CBF, CMRO2, and EEG were recorded and arterial blood was sampled for the determination of propofol concentrations (by high-performance liquid chromatography). Angiotensin II was used to maintain mean arterial pressure >/=80 mm Hg. Eight animals completed the protocol. Blood propofol concentrations rose progressively in all animals, reaching a mean of 34 +/- 12 microg/ml (+/-SD) at the end of 90 min. Electroencephalogram changes during the early stages of the infusion were extremely variable. However, concentrations above approximately 20 microg/ml were associated with progressive EEG suppression, and isoelectricity developed in two animals, at blood concentrations of 41 and 52 microg/ml. There was a progressive dose-related decrease in CBF, which reached a value of approximately 62% of baseline at a concentration of 40 microg/ml (as predicted by a polynomial curve fitted to a plot of CBF versus blood concentration). The CMRO2 also decreased progressively, reaching approximately 57% of baseline at 40 microg/ml. A plot of CMRO2 versus EEG total power suggests that isoelectricity should be associated with a CMRO2 approximately equal to 53% of baseline. We conclude that propofol produces a dose-related decrease in CBF and CMRO2. The relationship between EEG suppression and CMRO2 is qualitatively similar to that seen with barbiturates.

Low effluent nutrient technologies for wastewater treatment

The USEPA (2001) water quality nutrient criteria will have a significant impact on water pollution control industry due to stringent N and P requirements. This paper presents an update of findings on successful total N (TN) and total P (TP) technologies being implemented at existing wastewater treatment plants (WWTP) to achieve low TN and TP effluents and some key challenges in achieving lower levels. Plants consistently achieving <5 mg TN/L and < 0.5 mg TP/L were identified from a worldwide literature search and plant data collection. Technology gaps and research needs to improve successful technologies to achieve very low TN and TP effluents are summarised in this paper. The dissolved and colloidal organic N have been identified as major challenges in achieving very low levels of TN. Technical and economic challenges to achieve very low TP effluents include alkalinity deficiency, high chemical usage, high sludge production and lack of sufficient influent BOD for biological P uptake.

Generalized lymphangiomatosis and chylothorax in the pediatric age group

Four patients with generalized lymphangiomatosis presenting with chylothoraces are described. All four had bone involvement, two had involvement of the spleen, and one of the pericardium. The diagnosis was confirmed by typical radiology, histology, and in three patients by immunohistochemistry. Treatment was mainly palliative. Three patients died within 1/2 to three years of presentation.

Radiosurgery for arteriovenous malformations: the University of Toronto experience

BACKGROUND

From July 1989 to February 1996, 130 patients underwent stereotactic radiosurgery. We report the results of the first 50 patients eligible for a minimum of three years of follow-up.

METHODS

Twenty women and 30 men, (mean age: 37.5 years) were treated by dynamic rotation on a 6 MV linear accelerator. Prior treatment was embolization in seventeen, surgery in three and embolization and surgery in six. All had DSA and enhanced CT scanning, while some had MRI. Forty-seven treatments used a single isodose. Restricting eloquent normal tissue to 15 Gy, margin doses (at 50-90% isodose) were 12 Gy (one patient); 15 Gy (sixteen patients); 20 Gy (31 patients); 25 Gy (two patients). Maximum diameters were: < 1.5 cm (12 patients); < 2.0 cm (nine patients); < 2.5 cm (twelve patients); < 3.0 cm (thirteen patients; 3.0 cm (four patients).

RESULTS

Forty-five patients were evaluable at three years, with thirty-nine having angiography. Twenty-five had angiographically confirmed obliterations; two had parenchymal AVMs obliterated but with residual dural components; four had MRI evidence of obliteration (refused angiography). One patient acutely had a seizure; one patient (with hemorrhages, resection, and embolizations preceding two applications of radiosurgery, separated by 3.5 years) had worsening of memory.

CONCLUSIONS

Our uncorrected (five patients unevaluable at three years) and corrected angiographically confirmed obliteration rates are 54% and 60% respectively. Our follow-up (98% accounting of cohort; 78% angiographic rate) and explicit derivation of denominators help delineate the efficacy of radiosurgery at these doses.

Conformational studies on cyclic dipeptides

An analysis of 11 crystal structures of cyclic dipeptides so far reported in the literature is made, with main reference to the internal parameters of these molecules. Preferred conformations of the side chains of cyclic dipeptides with different alpha-amino acid residues have been studied by classical energy calculations. The possible conformations of the DKP ring are also studied. The significance of the non-bonded interaction in deciding the pathway for conformational change has also been investigated. The agreement between theoretical results and experimental observations is quite good, both with respect to the conformation of these molecules as well as the enthalpy difference as estimated from n.m.r. studies between different conformers.

A QA phantom for dynamic stereotactic radiosurgery: quantitative measurements

A spherical acrylic phantom was designed for quality assurance measurements of dynamic radiosurgery. The phantom consists of two mating hemispheres mounted on a base plate. The interhemispheric plane may be oriented at any angle to the base, the angle being identified by visible marks on the base plate of the phantom. The phantom has a set of replaceable, radiologically identifiable markers, suitable for Computed Tomography (CT), Magnetic Resonance (MR), and Digital Subtraction Angiography (DSA) imaging. The frame coordinates of each marker are calculated from its known positions with respect to the center of the sphere. The measured errors of these positions using CT and MR images, were within the voxel size of the displayed image, while for DSA images the error was greater than 2.5 mm at the periphery of the image. The calculated depths from the planning software, for various beam intersection points to the isocenter, agreed within 0.6 mm with the known depths. A variation of 3.6 +/- 2.6 mm in the calculated depths was observed between using MR and CT image data. This difference results in a 1% variation in Tissue Maximum ratio (TMR) calculations. Comparisons of measured and known volumes resulted in differences of 8%-10%.

Conformations of simple disulfides and L-cystine

abinitio Molecular orbital calculations at the STO-3G and STO-3G* levels on H2S2, (CH3)2S2, (CH3CH2)2S2, and L-cystine show that the minimum energy conformation occurs at the angle at which the S—S overlap population is at a maximum. In agreement with experiment, the calculations favour a disulfide dihedral angle close to 90°. The variation of the S—S overlap population is essentially independent of substituents, whereas the cis barrier to rotation about the S—S bond increases relative to the trans barrier as the size of the substituents increases. These observations lead to the conclusion that electronic effects determine the disulfide dihedral angle and that both steric and electronic effects control the relative magnitude of the cis and trans barriers.

Ultrasound-guided needle aspiration of amoebic liver abscess

This prospective study was carried out on 200 patients with clinically, ultrasonographically and serologically confirmed amoebic liver abscess. The role of ultrasound-guided needle aspiration in addition to medications was evaluated compared to drug treatment alone. Both the groups were monitored clinically and sonographically for up to 6 months after diagnosis. The initial response (after 15 days) was better in the aspirated group (P < 0.05) but resolution of abscess after 6 months were similar. There was a more rapid clinical response in the aspirated group, particularly in those with larger (> 6 cm) abscesses and there were no complications. Percutaneous ultrasound-guided needle aspiration is a safe diagnostic and therapeutic approach which enhances clinical recovery, accelerates resolution, especially in large abscesses, and prevents complications.