Conductance of Graphene Nanoribbon Junctions and the Tight Binding Model.

Planar carbon-based electronic devices, including metal/semiconductor junctions, transistors and interconnects, can now be formed from patterned sheets of graphene. Most simulations of charge transport within graphene-based electronic devices assume an energy band structure based on a nearest-neighbour tight binding analysis. In this paper, the energy band structure and conductance of graphene nanoribbons and metal/semiconductor junctions are obtained using a third nearest-neighbour tight binding analysis in conjunction with an efficient nonequilibrium Green's function formalism. We find significant differences in both the energy band structure and conductance obtained with the two approximations.

Multiplexing of polarization-maintaining photonic crystal fiber based Sagnac interferometric sensors.

Three multiplexing schemes are presented for polarization-maintaining photonic crystal fiber based Sagnac interferometric sensors. The first technique is wavelength division multiplexing using coarse wavelength division multiplexers (CWDMs) to distinguish signals from each multiplexed sensor in different wavelength channels. The other two schemes are to multiplex sensors in series along a single fiber link and in parallel by using fiber-optic couplers. While for the CWDM scheme, the multiplexed sensing signal can be obtained by direct measurement; for the other two multiplexing techniques, the sensing signal is more complex and cannot be easily demultiplexed. Thus, some signal processing methods are required. In this regard, two mathematical transformations, namely the discrete wavelet transform and Fourier transform, have been independently and successfully implemented into these two schemes. The operating principles, experimental setup, and overall performance are discussed.

The use of gel dosimetry for verification of electron and photon treatment plans in carcinoma of the scalp.

In recent years there has been a large amount of research into the potential use of radiation sensitive gels for three-dimensional verification of clinical radiotherapy doses. In this paper we report the use of a MAGIC gel dosimeter (Fong et al 2001 Phys. Med. Biol. 46 3105) for the verification of a specific patient's radiation therapy dose distribution. A 69-year-old male patient presented with a squamous cell carcinoma extending approximately 180 degrees across the top of the scalp (anterior to posterior) and from just over midline to 90 degrees left of the skull. The patient's treatment was commenced using two electron fields. For gel dosimetry, phantoms were produced in which the outer surface spatially corresponded to the outer contours of the patient's anatomy in the region of irradiation. The phantoms were treated with either electrons or intensity modulated radiation therapy (IMRT) with photons. The results identified a hot spot between the matched electron fields and confirmed the more homogeneous dose distribution produced by the IMRT planning system. The IMRT plan was then clinically implemented. The application of a clinical dose to a phantom shaped to a specific patient as well as the ability to select a slice at will during phantom imaging means that gel dosimetry can no longer be considered to simply have potential alone, but is now in fact a useful dosimetric tool.

Comparison of a lung fitting algorithm with CT data for tangential fields in radiotherapy of the breast.

A method of estimating the shape and position of the lung in tangential breast fields is presented for patients who have not been CT scanned. Using the Osiris system, the external contour is obtained optically, and an estimated lung structure superimposed on the transverse outlines based on the measured lung depth in the tangential fields and an analysis of the typical lung shapes obtained from CT images. The accuracy of this fit was determined by comparison with a set of 64 CT images imported into the Osiris system. Dose distributions were calculated by two treatment planning systems: ADAC Pinnacle and GE Target2. The computed dose distributions for 6 MV photons were compared against measured doses in a specialized breast phantom. For the worst case of lung fit compared with CT, the dosimetric error (based upon ADAC Pinnacle calculations) was 2.0% in the shadow of the lung. For the complete patient data set, the relative dose errors to these points were reduced from a mean value of 8.4% and standard deviation (SD)=1.8% (no lung correction) to a mean of 0.2% and SD=1.0% (lung correction using fitted lung). It was also found that for every 1 cm of lung path length the dose to the breast along that path length increased by approximately 1%. The results of these investigations indicated that the lung fit model was satisfactory for routine clinical use, so that good dosimetric results can be obtained using lung correction without the need for CT imaging.

Calibration of CT Hounsfield units for radiotherapy treatment planning of patients with metallic hip prostheses: the use of the extended CT-scale.

Heterogeneity corrections for radiotherapy dose calculations are based on the electron density of the disturbing heterogeneity. However, when CT planning a radiotherapy treatment, where metallic hip implants are present, considerable artefacts are seen in the images. Often, an additional problem arises whereby no information regarding the artificial hip's composition and geometry is available. This study investigates whether the extended CT range can be used to determine the composition (hence electron density) of artificial hips in radiotherapy patients. Two CT-calibration methods were evaluated, one based on material substitution, the other a stoichiometric calibration. We also evaluate whether the physical dimensions of metal prostheses can be accurately imaged for subsequent use in treatment planning computers. Neither calibration method successfully predicted electron densities. However, the limited range of implant-materials used in patients means that the extended CT range can still successfully distinguish between implant densities. The physical dimensions can be determined to +/-2 mm by establishing the required windowing of displays for each material. The cross-sectional area of the prosthesis and the presence of other high-density objects in a CT slice can influence the generated CT number and careful design of calibration phantoms is essential.

Commissioning and quality assurance of the Pinnacle(3) radiotherapy treatment planning system for external beam photons.

The commissioning of a Pinnacle(3) treatment planning system is described. Four Elekta linear accelerators were commissioned for external beam photons. Measured data were used to derive parameter values for the Pinnacle(3) beam model by (1). fitting a Monte Carlo model of the accelerator head to measured data and then extracting the parameters for the Pinnacle(3) beam model, and by (2). using the auto-modelling facility within Pinnacle(3). Both of these methods yielded dose distributions in accord with published recommendations. A separate small-field beam model, customized for an in-house compact blocking system, was also created, which satisfied appropriate acceptance criteria for stereotactically guided conformal brain treatments. Inhomogeneous, oblique, asymmetrical and irregular fields were also assessed, with calculated and measured doses agreeing to within +/-3%. Dose-volume histogram calculation was found to be accurate to within +/-5% dose or volume for a grid size of 4 mm x 4 mm x 4 mm, with better accuracy being achieved for finer grids. Isocentric doses were compared between Pinnacle(3)'s collapsed cone convolution algorithm and the Bentley-Milan algorithm within the Target-2 treatment planning system. Dose differences were generally less than 3% in the dose prescribed, with larger values for breast plans, where the Pinnacle(3) algorithm calculated scatter more accurately. Pelvic and thoracic plans were also verified using an anthropomorphic phantom, with local dose differences between calculated and delivered dose of up to 8%, but mainly less than 3%, and with no systematic difference. Ionization chamber verifications using START and RT-01 trial procedures demonstrated differences between calculated and measured doses of less than 2%. Following satisfactory performance in the commissioning process, Pinnacle(3) has now been introduced into routine clinical use.

A systematic review of stapled hemorrhoidectomy.

HYPOTHESIS: Use of circular stapled hemorrhoidectomy will result in the same or improved safety and efficacy outcomes as those of the conventional methods for hemorrhoidectomy in patients with hemorrhoids. DATA SOURCES: Studies on stapled hemorrhoidectomy were identified using PREMEDLINE and MEDLINE (June 1966-June 2001), EMBASE (January 1980-June 2001), Current Contents (June 1993-June 2001), Ovid HEALTHSTAR (January 1975-June 2001), the National Institutes of Health Clinical Trials database (searched June 13, 2001), and The National Coordinating Centre for Health Technology Assessment database (searched June 14, 2001). The search terms were as follows: haemorrhoid* and (stapl* or convent*) or hemorrhoid* and (stapl* or convent*). The Cochrane Library (2001, issue 2) was searched using the search terms haemorrhoid* or hemorrhoid*. STUDY SELECTION: Articles detailing randomized controlled trials were included if they compared circular stapled with conventional hemorrhoidectomy and provided relevant safety and efficacy outcome information. DATA EXTRACTION: Data from all included studies were extracted using standardized data extraction tables that were developed a priori. In addition, the randomized controlled trials were examined with respect to the adequacy of allocation concealment, handling of those unavailable for follow-up, and any other aspect of the study design or execution that may have introduced bias. DATA SYNTHESIS: Seven randomized controlled trials met the inclusion criteria. A meta-analysis was conducted when the studies had comparable outcomes, inclusion criteria, and follow-up. There was reasonably clear evidence in favor of the stapled procedure for bleeding at 2 weeks (relative risk, 0.55; 95% confidence interval, 0.37-0.82) and length of hospital stay (weighted mean difference, -0.89 days; 95% confidence interval, -1.42 to -0.36). Other less robust results in favor of the stapled hemorrhoidectomy related to pain, bleeding, anal discharge, wound healing, tenderness to per rectal examination, incontinence scores, earlier return of bowel function, analgesic requirement, and resumption of normal activities. One trial showed that prolapse occurred at significantly higher rates in the stapled hemorrhoidectomy group. However, the outcomes were poorly reported and generally showed statistically significant heterogeneity. CONCLUSIONS: Stapled hemorrhoidectomy may be at least as safe as conventional hemorrhoidal surgical techniques. However, the efficacy of the stapled procedure compared with the conventional techniques could not be determined. More rigorous studies with longer follow-up periods and larger sample sizes need to be conducted.

Voice gains following thyroplasty may improve over time.

Type I thyroplasty for unilateral vocal fold paralysis restores voice. The purpose of this study was to evaluate measures of voice before thyroplasty, and at 3 months and 1 year after surgery. Of interest was whether vocal improvement in the first weeks after surgery was maintained or even enhanced over time. A total of 40 patients with unilateral paralysis underwent type I thyroplasty with or without arytenoid adduction. Perceptual, acoustic and aerodynamic measures of voice were studied. Perceptual analysis determined that optimal postoperative voice quality evolved over the first year. Acoustic indices of perturbation demonstrated progressive improvement over 12 months, whereas pitch and intensity ranges were increasingly extended. Postoperative glottal flow rates were normalized and phonation times were significantly longer, with benefits maintained over time. All perceptual, aerodynamic and acoustic measures of voice were improved 3 months after thyroplasty, with many measures further improved at 1 year. Such findings provide evidence that voice outcome progressively evolves over the first 12 months after surgery.

Modelling to solve odour problems.

The use of dispersion modelling is a powerful tool to establish levels of treatment required to remove odour complaints. Odour is an extremely sensitive issue and is key to the public perception of wastewater environmental protection. This paper describes a case study of the successful resolution of long-standing odour problems at the East Worthing Wastewater Treatment Works (WTW), on the South Coast of England, utilising modelling and appropriate treatment technologies. A number of odour surveys have been conducted on the site to identify the major sources on the works, which were found to be the sludge press house and the primary settlement tanks, situated only 10 metres from the nearest properties. As a result attempts to resolve the odour problem have been made including the covering of identified sources, treating extract using activated carbon filters and installing perfume sprays. During the site development all sources were contained and ventilated to a 60,000 m3/hr Jones & Attwood ODORGARD unit. Its requirement was to ensure that no receptor was exposed to a concentration in excess of 4 ouEm3 (Odour units), in accordance with the odour planning condition. Dispersal modelling was performed to determine the maximum permissible outlet concentration. The results of the modelling exercise established that emissions from the odour control plant should not exceed 675 ouEm3 to ensure that the receptor standard was attained. An optimisation programme was conducted to ensure that the unit was providing the optimum level of treatment prior to taking the olfactometry samples. Following the plant's optimisation the results of the olfactometry analysis confirmed that the discharge levels were below the required 670 ouEm3. Since completion of the sludge treatment centre scheme there have been no registered odour complaints directed at the East Worthing WTW, and the local air quality has been greatly improved for the residents surrounding the works.

Voice outcome following lateral laryngotomy to remove teflon granuloma.

Formation of a Teflon granuloma may lead to progressive dysphonia and airway compromise. Excision of the granuloma by lateral laryngotomy allows preservation of the uninvolved lamina propria. A sternothyroid muscle flap or Silastic implant to medialize the vocal fold restores a straight glottal edge and optimizes voice production. Fifteen patients underwent removal of a Teflon granuloma via a lateral approach. Analysis of data revealed improved acoustic and aerodynamic parameters of voice following surgery. Indices of acoustic perturbation were reduced, and vocal pitch normalized. While the dynamic pitch range was unchanged, the capacity to vary loudness was enhanced. Flow rates in speech, abnormally elevated before surgery, normalized after the procedure, and phonation times were significantly longer. Perceptual and stroboscopic data confirmed that voices were improved, but not normal.

A quantitative treatment planning study evaluating the potential of dose escalation in conformal radiotherapy of the oesophagus.

BACKGROUND AND PURPOSE: This study aims to evaluate the reduction in radiation dose to normal thoracic structures through the use of conformal radiotherapy techniques in the treatment of oesophageal cancer, and to quantify the resultant potential for dose escalation. MATERIALS AND METHODS: Three different CT-derived treatment plans were created and compared for each of ten patients. A two-phase treatment with conventional straight-edged fields and standard blocks (CV2), a two-phase conformal plan (CF2), and a three-phase conformal plan where the third phase was delivered to the gross tumour only (CF3), were considered for each patient. Escalated dose levels were determined for techniques CF2 and CF3, which by virtue of the conformal field shaping, did not increase the mean lung dose. The resulting increase in tumour control probability (TCP) was estimated. RESULTS: A two-phase conformal technique (CF2) reduced the volume of lung irradiated to 18 Gy from 19.7+/-11.8 (1 SD) to 17.1+/-12.3% (P=0.004), and reduced the normal tissue complication probability (NTCP) from 2.4+/-4.0 to 0.7+/-1.6% (P=0.02) for a standard prescribed dose of 55 Gy. Consequently, technique CF2 permitted a target dose of 59.1+/-3.2 Gy without increasing the mean lung dose. Technique CF3 facilitated a prescribed dose of 60.7+/-4.3 Gy to the target, the additional 5 Gy increasing the TCP from 53. 1+/-5.5 to 68.9+/-4.1%. When the spinal cord tolerance was raised from 45 to 48 Gy, technique CF3 allowed 63.6+/-4.l Gy to be delivered to the target, thereby increasing the TCP to 78.1+/-3.2%. CONCLUSIONS: Conformal radiotherapy techniques offer the potential for a 5-10 Gy escalation in dose delivered to the oesophagus, without increasing the mean lung dose. This is expected to increase local tumour control by 15-25%.

The delivery of intensity modulated radiotherapy to the breast using multiple static fields.

BACKGROUND AND PURPOSE: To develop a method of using a multileaf collimator (MLC) to deliver intensity modulated radiotherapy (IMRT) for tangential breast fields, using an MLC to deliver a set of multiple static fields (MSFs). MATERIALS AND METHODS: An electronic portal imaging device (EPID) is used to obtain thickness maps of medial and lateral tangential breast fields. From these IMRT deliveries are designed to minimize the volume of breast above 105% of prescribed dose. The deliveries are universally-wedged beams augmented with a set of low dose shaped irradiations. Dosimetric and planning QA of this method has been compared with the standard, wedged treatment and the corresponding treatment using physical compensators. Several options for delivering the MSF treatment are presented. RESULTS: The MSF technique was found to be superior to the standard technique (P value=0.002) and comparable with the compensated technique. Both IMRT methods reduced the volume of breast above 105% dose from a mean value of 12.0% of the total breast volume to approximately 2.8% of the total breast volume. CONCLUSIONS: This MSF method may be used to reduce the high dose volume in tangential breast irradiation significantly. This may have consequences for long-term side effects, particularly cosmesis.

Ultrasound-modulated twin-fluid atomization of a liquid jet.

A resonant liquid capillary wave theory which extends Taylor's dispersion relation to include the sheltering effect of liquid surface inclination caused by air flow is presented. The resulting dispersion curves are compared to new experimental results of how drop-size and size distributions vary with surface tension and air velocity in both airblast and ultrasound-modulated twin-fluid atomization of liquids with a constant kinematic viscosity of 2 cSt. Good agreements between the theoretical predictions of relative growth rates of the capillary waves and the experimental results of drop-size and size distributions led to the conclusion that Taylor-mode breakup of capillary waves plays a very important role in twin-fluid (airblast) atomization of a liquid jet. Thus, the ultrasound-modulated twin-fluid atomization not only verifies the capillary wave mechanism but also provides a means for controlling the drop-size and size distributions in twin-fluid atomization, which has a variety of applications in fuel combustion, spray drying, and spray coating.

A comparison of conventional and conformal radiotherapy of the oesophagus: work in progress.

A retrospective treatment planning study was carried out in five patients to assess the effectiveness of conformal radiotherapy of the oesophagus. A two-phase conventional treatment plan was created for each patient, with a prescribed dose of 55 Gy. This plan was compared with a single-phase conformal plan consisting of the same field arrangement as the second phase of the conventional treatment, but with conformal blocks shaped to the beam's eye view of the planning target volume. A further comparison was made between the conventional plan and a two-phase plan using the same beam angles and weights as the conventional plan, but with conformal field shapes. The effectiveness of each treatment plan was assessed using dose--volume histograms and normal tissue complication probabilities for the lungs. On average, the single-phase conformal technique increased the mean lung dose from 22.5% (+/- 6.2 SD) of the prescribed dose to 29.5% (+/- 5.2 SD) compared with the conventional technique (p = 0.0001). This indicates that this technique did not offer any benefit in terms of reducing the risk of pneumonitis. However, the two-phase conformal technique reduced the mean lung dose from 22.5% (+/- 6.2 SD) of the prescribed dose to 19.8% (+/- 4.6 SD)(p = 0.03), showing that this technique should reduce the risk of pneumonitis. Further work is underway to study more patients and to investigate tumour control probability and dose escalation.

Whole body doses from linear accelerator-based stereotactic radiotherapy.

PURPOSE: The objective of this work was to measure whole body radiation doses in a humanoid phantom from linear accelerator-based cranial stereotactic radiosurgery/therapy (SRS/T), using different beam arrangements. METHODS AND MATERIALS: A standard noncoplanar five-arc beam arrangement and a four-arc technique without a sagittal arc were used to deliver 20 Gy in a single fraction to a midline spherical target volume in the corpus callosum region of an Alderson-Rando anthropomorphic phantom using (i) a 20-mm and (ii) a 40-mm circular collimator. Whole body dose measurements were made using lithium fluoride thermoluminescent dosimetry. Whole body isodose plots in the sagittal and coronal planes and organ doses were compared for the two arcing beam arrangements. An ionization chamber was used to record the exit dose at intervals along the length of the phantom at midline and 4.5 cm off-axis for (i) a single fixed field and (ii) a solitary 90 degrees sagittal arc using a 40-mm circular collimator. RESULTS: The sagittal arc was the major contributor to neck and trunk doses when the five- and four-arc arrangements were compared, with fourfold greater thyroid dose. The gonad dose was increased by the sagittal arc, but was largely due to leakage radiation. The dose from a fixed field exiting down the long axis of the phantom was tenfold greater than that from a solitary 90 degrees sagittal arc. When the fixed field or arc traversed the lung or exited through the pharynx and major upper airways, the dose measurements below the diaphragm were 30-40% higher than those along the exit path of maximum soft tissue density. CONCLUSION: When SRS/T is used in nonmalignant conditions such as cranial arteriovenous malformations or benign tumors the exit paths of arcing beams or fixed fields should be taken into account when deciding upon the final treatment plan. Such consideration should minimize the risk of radiation-induced malignancy, notably in the thyroid gland of younger patients.

Effects of morning phototherapy on circadian markers in seasonal affective disorder.

BACKGROUND: The suppression of melatonin by light at 00.30 hours has been shown to be greater in winter than in summer on patients with seasonal affective disorder (SAD) but not in matched normal controls. METHOD: In this study 12 patients with SAD and 12 matched normal controls were exposed to morning light therapy in the winter. Melatonin profiles and sensitivity to light were measured before and after treatment. RESULTS: The SAD but not the normal group showed a phase advance of melatonin rhythms in response to phototherapy. There was an association between phase position and phase shift in the SAD but not in the normal group. CONCLUSIONS: There may be instability of circadian rhythms in SAD mediated by a high-amplitude phase response curve, rather than a fixed phase abnormality as had been previously suggested. This instability may be secondary to impaired serotoninergic function in the afferent pathways to the suprachiasmatic nuclei.

Surgical management of cutaneous infection caused by atypical mycobacteria after penetrating injury: the hidden dangers of horticulture.

We identified two patients in a 12-month period who presented with cutaneous infection and secondary lymph node involvement from atypical mycobacterial infection after minor gardening injuries. One patient had a coinfection with Nocardia asteroides. Both patients required multiple surgical interventions, despite appropriate antibiotic therapy, before resolution of the disease. The course of the infection was characterized by chronic relapses with complete healing at 12 to 18 months after the original injury. The identification and management of this clinical problem are reviewed.

A quality assurance procedure for the Varian multi-leaf collimator.

A quick, simple set of tests has been devised to assess and record the quality assurance aspects of the Varian multi-leaf collimator (MLC) when used for clinical treatments on a regular basis. Pre-treatment, daily and weekly checks are performed by the radiographers while more detailed quality assurance is carried out at monthly and quarterly intervals by physicists.

Case report: giant choledochal cyst.

We report an adult female with a rare giant choledochal cyst. The patient presented following a normal pregnancy with the classical triad of an abdominal mass associated with jaundice and right upper quadrant abdominal pain. The cyst was excised using an intramural technique and biliary reconstruction achieved with a Roux-en-Y hepaticojejunostomy. Our patient has remained well with no evidence of malignancy over a 12 year review period. The aetiology and current management of this condition are discussed.