Monte Carlo simulation and patient dosimetry for a kilovoltage cone-beam CT unit.

PURPOSE: The purpose of this work is to characterize the x-ray volume imager (XVI), the cone-beam computed tomography (CBCT) unit mounted on the Elekta Synergy linac, with F1 bowtie filter and to calculate the three-dimensional dose delivered to patients using volumetric acquisition. METHODS: The XVI is modeled in detail using a new Monte Carlo (MC) code, BEAMPP, under development at the National Research Council Canada. In this investigation, a new component module is developed to accurately model the unit's bowtie filter used in conjunction with the available beam collimators at the clinical energy of 120 kV. The modeling is compared against percentage depth dose (PDD) and profile measurements. Kilovoltage radiation beams' phase space files are also analyzed. The authors also describe a method for the absolute dose calibration of the MC model of the CBCT unit when used in a clinical volumetric acquisition mode. Finally, they calculate three-dimensional patient dose from CBCT image acquisition in three clinical cases of interest: Pelvis, lung, and head and neck. RESULTS: The agreement between measurement and MC is shown to be very good: Within +/- 2% for the PDD and within +/- 3.5% inside the radiation field for all the collimators with the F1 bowtie filter. A full account of the absolute calibration method is given and dose calculation is validated against ion chamber measurements in different locations of a plastic phantom. Calculations and experiments agree within +/- 2% or better in both at the center and the periphery of the phantom, with worst agreement of 4.5% at the surface of the phantom and for one specific combination of collimator and filter. Patient dose from CBCT scan reveals that dose to tissue is between 2 and 2.5 cGy for a pelvis or a lung full acquisition. For H&N dose to tissue is 5 cGy, with the unit presets used in this work. Dose to bony structures can be two to three times higher than dose to tissue. CONCLUSIONS: The XVI CBCT unit has been fully modeled including the F1 bowtie filter. Absolute dose distribution from the unit has been successfully validated. Full MC patient dose calculation has shown that the three-dimensional dose distribution from CBCT is complex. Patient dose from CBCT exposure cannot be completely accounted for by using a numerical factor as an estimate of the dose at the center of the body. Furthermore, additional dose to bone should be taken into account when adopting any IGRT strategy and weighed vs the unquestionable benefits of the technique in order to optimize treatment. Full three-dimensional dose calculation is recommended if patient dose from CBCT is to be integrated in any adaptive planning strategy.

Simulating oblique incident irradiation using the BEAMnrc Monte Carlo code.

A new source for the simulation of oblique incident irradiation has been developed for the BEAMnrc Monte Carlo code. In this work, we describe a method for the simulation of any component that is rotated at some angle relative to the central axis of the modelled radiation unit. The performance of the new BEAMnrc source was validated against experimental measurements. The comparison with ion chamber data showed very good agreement between experiments and calculation for a number of oblique irradiation angles ranging from 0 degrees to 30 degrees . The routine was also cross-validated, in geometrically equivalent conditions, against a different radiation source available in the DOSXYZnrc code. The test showed excellent consistency between the two routines. The new radiation source can be particularly useful for the Monte Carlo simulation of radiation units in which the radiation beam is tilted with respect to the unit's central axis. To highlight this, a modern cone-beam CT unit is modelled using this new source and validated against measurement.

Molecular epidemiology of multi- and extensively-drug-resistant Mycobacterium tuberculosis in Ireland, 2001-2014.

OBJECTIVES: The primary objective of this work was to examine the acquisition and spread of multi-drug resistant (MDR) tuberculosis (TB) in Ireland. METHODS: All available Mycobacterium tuberculosis complex (MTBC) isolates (n = 42), from MDR-TB cases diagnosed in Ireland between 2001 and 2014, were analysed using phenotypic drug-susceptibility testing, Mycobacterial-Interspersed-Repetitive-Units Variable-Number Tandem-Repeat (MIRU-VNTR) genotyping, and whole-genome sequencing (WGS). RESULTS: The lineage distribution of the MDR-TB isolates comprised 54.7% Euro-American, 33.3% East Asian, 7.2% East African Indian, and 4.8% Indo-Oceanic. A significant association was identified between the East Asian Beijing sub-lineage and the relative risk of an isolate being MDR. Over 75% of MDR-TB cases were confirmed in non-Irish born individuals and 7 MIRU-VNTR genotypes were identical to clusters in other European countries indicating cross-border spread of MDR-TB to Ireland. WGS data provided the first evidence in Ireland of in vivo microevolution of MTBC isolates from drug-susceptible to MDR, and from MDR to extensively-drug resistant (XDR). In addition, they found that the katG S315T isoniazid and rpoB S450L rifampicin resistance mutations were dominant across the different MTBC lineages. CONCLUSIONS: Our molecular epidemiological analyses identified the spread of MDR-TB to Ireland from other jurisdictions and its potential to evolve to XDR-TB.

The prevention of 'dry socket' with topical metronidazole in general dental practice.

OBJECTIVE: The purpose of the study was to determine if the intra-alveolar application of topical metronidazole gel could reduce the incidence of alveolar osteitis (dry socket) following routine tooth extraction in molar and premolar extraction sites. DESIGN: This was a multicentre, double blind, randomised, placebo-controlled clinical trial. A total of 302 patients took part, of which 23 returned with alveolar osteitis. Of these, eight had received the metronidazole gel and 15 the placebo. SETTING: The study was carried out in three general dental practices by general dental practitioners working in England over the period 2000-2003. MAIN OUTCOME MEASURES: Following extraction of either a molar or premolar tooth, either a 25% metronidazole gel or KY Jelly was syringed gently into the socket. A painful post operative complication was recorded if either a dry socket was present or the patient returned with pain. RESULTS AND CONCLUSIONS: The difference in the incidence of alveolar osteitis between the placebo and the active gel groups was not significant and it was concluded that 25% topical metronidazole gel was not effective in reducing the incidence of alveolar osteitis. It was found that the incidence of alveolar osteitis reduced with increasing age and was more likely to occur in a patient with a previous history of the condition.

Successful web searching.

This section of the series introduces the topic of WWW search engines and directory sites; showing you how to find information using a search engine and a directory. It also covers other ways of searching for information on the internet.

E-mail: what is e-mail?

This third part of the series explains what e-mail is and why it is the most widely used service on the internet. The principles behind sending and receiving e-mail messages are described. Also the various uses of e-mail are discussed.

An introduction to the Internet.

This is the first of a multipart series on the internet aimed at dental practitioners. In this part I will try to answer the questions 'What is the Internet?' and 'How does it work?', the historical background of the internet will be discussed, and reasons will be given as to why dentists should consider connecting to the internet.

Efficient use of the Internet.

This section explains how to make most of your time on-line by providing tips on how to reduce the cost of using the internet. Suggestions are given on how to get the best from your existing hardware and software. There are also recommendations for some additional hardware and software.

The evaluation of SafeQuest--a computer-assisted learning program on cross-infection control for the dental team.

OBJECTIVE: Evaluation of a computer-assisted learning (CAL) program (authored by a general dental practitioner-GDP) on cross-infection control (CIC) for the dental team. The aims of the evaluation were to determine how easy the program was to use, to determine if users found the information useful, to ensure that the content was accurate and to see what improvements could be made. METHODS: 96 questionnaires were distributed to dentists, 57 of whom responded (60%). 66% of the respondents were GDPs. RESULTS: Compared with earlier evaluations of hospital-produced CAL programs, SafeQuest was equally well received. 96% of respondents found it easy to use and 93% gave a positive score for their overall impression. 64% felt that the program had extended their knowledge, despite the fact that 74% rated their knowledge on CIC as being good/excellent before using SafeQuest. Suggestions on how the content and presentation of the program could be improved led to changes to the final version. CONCLUSIONS: The SafeQuest program on cross-infection control could be useful as a learning resource in general dental practice. The program, authored and produced by a GDP, compares favourably with those written in dental schools.

High-performance computing for Monte Carlo radiotherapy calculations.

We report on the RTGrid project, which investigates approaches for using high-performance computing infrastructures, such as the grid, in order to reduce the turnaround time of Monte Carlo (MC) simulation-based radiotherapy treatment planning. The main aim of this project is to render accurate dose calculations using MC simulations clinically feasible. To this end, we have successfully implemented and deployed the RTGrid distributed simulation framework for MC dose calculations. In this paper, we present the main experimental findings.

Introduction to the world wide web.

The World Wide Web used to be nicknamed the 'World Wide Wait'. Now, thanks to high speed broadband connections, browsing the web has become a much more enjoyable and productive activity. Computers need to know where web pages are stored on the Internet, in just the same way as we need to know where someone lives in order to post them a letter. This section explains how the World Wide Web works and how web pages can be viewed using a web browser.

An introduction to the Internet.

The aim of this multipart series is to show members of the dental team why the Internet is becoming an essential tool and to encourage colleagues to 'get online'. The various ways of connecting to the Internet are discussed, comparing the advantages and disadvantages of each. How to use email and browse the World Wide Web is covered in some detail. There are plenty of practical tips on how to use the Internet safely and efficiently. The amount of information available on the Internet is vast and the series gives practical illustrations on how to be successful in searching for relevant information. There is an introduction on how to create a practice website and the final part looks at how to put all these skills together to make the most use of the Internet in the practice of dentistry.