Monte Carlo verification of intensity modulated radiotherapy treatments using EPIDS

Purpose: Electronic Portal Imaging Devices (EPIDs) are available with most linear accelerators (Amonuk, 2002), the current technology being amorphous silicon flat panel imagers. EPIDs are currently used routinely in patient positioning before radiotherapy treatments. There has been an increasing interest in using EPID technology tor dosimetric verification of radiotherapy treatments (van Elmpt, 2008). A straightforward technique involves the EPID panel being used to measure the fluence exiting the patient during a treatment which is then compared to a prediction of the fluence based on the treatment plan. However, there are a number of significant limitations which exist in this Method: Resulting in a limited proliferation ot this technique in a clinical environment. In this paper, we aim to present a technique of simulating IMRT fields using Monte Carlo to predict the dose in an EPID which can then be compared to the measured dose in the EPID. Materials: Measurements were made using an iView GT flat panel a-SI EPfD mounted on an Elekta Synergy linear accelerator. The images from the EPID were acquired using the XIS software (Heimann Imaging Systems). Monte Carlo simulations were performed using the BEAMnrc and DOSXVZnrc user codes. The IMRT fieids to be delivered were taken from the treatment planning system in DICOMRT format and converted into BEAMnrc and DOSXYZnrc input files using an in-house application (Crowe, 2009). Additionally. all image processing and analysis was performed using another in-house application written using the Interactive Data Language (IDL) (In Visual Information Systems). Comparison between the measured and Monte Carlo EPID images was performed using a gamma analysis (Low, 1998) incorporating dose and distance to agreement criteria. Results: The fluence maps recorded by the EPID were found to provide good agreement between measured and simulated data. Figure 1 shows an example of measured and simulated IMRT dose images and profiles in the x and y directions. "A technique for the quantitative evaluation of dose distributions", Med Phys, 25(5) May 1998 S. Crowe, 1. Kairn, A. Fielding, "The Development of a Monte Carlo system to verify Radiotherapy treatment dose calculations", Radiotherapy & Oncology, Volume 92, Supplement 1, August 2009, Pages S71-S71.

No hiding place

As public and private space becomes a focus for development values, contests occur between the unequal parties having a stake in the use of public space, such as central and local government, young people, communities and site developers. It is within the monitoring, recording and control procedures that young people’s use of public space is constructed as a threat to social order in need of surveillance and exclusion. This forms a major and contemporary feature in shaping thinking about urban and rural working class young people in the UK.

Automated proofs of computational indistinguishability

We present a tool for automatic analysis of computational indistinguishability between two strings of information. This is designed as a generic tool for proving cryptographic security based on a formalism that provides computational soundness preservation. The tool has been implemented and tested successfully with several cryptographic schemes.

Sun, sea, sex, sand and soap

A recent issue of Young People Now (November 1995) mentioned the new (UK) Channel 4 television soap opera Hollyoaks by Phil Redmond, which raises the issue of the role of ‘soaps’ in the daily lives of young people. Australian soaps are especially popular in Britain and of interest to those who work with young people, because they have a high proportion of youthful looking actors and actresses and frequently depict scenes involving young people and apparent ‘real’ teenage dilemmas.

Young people, public space and new urbanism

The first of three articles in this issue addressing the public space topic considers public space and young people in the light of a range of papers delivered at the 27th International Conference on 'Making Cities Livable', held in Vienna, Austria, in July 2000. Under the overarching concept of the "liveable city" the conference themes of 'Rediscovery of public space' and 'Cities for the wellbeing of children' attracted a broad mix of those interested in the planning, design and management of urban space. A number of themes percolated through the conference which stimulated the writers to examine the nexus between urban development, young people and public space. There is an ongoing need to examine the meaning of public space in the face of powerful urban development trends. A model of public space practice is required which incorporates a vision of inclusive public spaces, fosters the interactivity of design, planning, social policy and management, and resources for greater communication and strategic action between stake holders from the most local of levels to those at state and international levels. The speed and magnitude of contemporary urban development makes community input and influence difficult, particularly for those impacted on by the exclusionary tendencies of much urban development. It is critical that a range of meaningful and sustainable mechanisms are developed which allow young people’s conceptions of what constitutes youth-friendly space to be directly made and taken account of.

Caught on camera

The emergence of shopping malls in Europe, the UK and Australia over the last thirty years or so, raises questions about the disruptive effects of such capital intensive developments on local area shopping facilities, transport and other infrastructures and the maintenance of artificially high prices for goods, whereby the promised greater choice of shops and prices is rarely a genuine free market of competition leading to lower prices. A central question to be addressed is whom these centres represent and belong to. While many claim to exist to ‘serve the community’ almost all malls and centres are private property and the community of shoppers has few, if any rights compared with the conventional high street, which is a public thoroughfare. This permits the management of the centres through their own private security staff, to observe, follow, eject and refuse further admission to anyone considered to be ‘undesirable’. What is different about the newest shopping centres is the routine use of increasingly sophisticated CCTV surveillance equipment to observe and record, for later evidential and entry restriction use, the movements of centre visitors.

Predicate encryption for multi-inner-products

Predicate encryption is a new primitive that supports flexible control over access to encrypted data. We study predicate encryption systems, evaluating a wide class of predicates. Our systems are more expressive than the existing attribute-hiding systems in the sense that the proposed constructions support not only all existing predicate evaluations but also arbitrary conjunctions and disjunctions of comparison and subset queries. Toward our goal, we propose encryption schemes supporting multi-inner-product predicate and provide formal security analysis. We show how to apply the proposed schemes to achieve all those predicate evaluations.

ASICS : authenticated key exchange security incorporating certification systems

Most security models for authenticated key exchange (AKE) do not explicitly model the associated certification system, which includes the certification authority (CA) and its behaviour. However, there are several well-known and realistic attacks on AKE protocols which exploit various forms of malicious key registration and which therefore lie outside the scope of these models. We provide the first systematic analysis of AKE security incorporating certification systems (ASICS). We define a family of security models that, in addition to allowing different sets of standard AKE adversary queries, also permit the adversary to register arbitrary bitstrings as keys. For this model family we prove generic results that enable the design and verification of protocols that achieve security even if some keys have been produced maliciously. Our approach is applicable to a wide range of models and protocols; as a concrete illustration of its power, we apply it to the CMQV protocol in the natural strengthening of the eCK model to the ASICS setting.

Counterfeiting attacks on block-wise dependent fragile watermarking schemes

In this paper, we present three counterfeiting attacks on the block-wise dependent fragile watermarking schemes. We consider vulnerabilities such as the exploitation of a weak correlation among block-wise dependent watermarks to modify valid watermarked %(medical or other digital) images, where they could still be verified as authentic, though they are actually not. Experimental results successfully demonstrate the practicability and consequences of the proposed attacks for some relevant schemes. The development of the proposed attack models can be used as a means to systematically examine the security levels of similar watermarking schemes.

Count-min sketches for estimating password frequency within Hamming distance two

The count-min sketch is a useful data structure for recording and estimating the frequency of string occurrences, such as passwords, in sub-linear space with high accuracy. However, it cannot be used to draw conclusions on groups of strings that are similar, for example close in Hamming distance. This paper introduces a variant of the count-min sketch which allows for estimating counts within a specified Hamming distance of the queried string. This variant can be used to prevent users from choosing popular passwords, like the original sketch, but it also allows for a more efficient method of analysing password statistics.

Children and young people using public space : models of rights, optimism and wellbeing

This presentation discusses topics and issues that connect closely with the Conference Themes and themes in the ARACY Report Card. For example, developing models of public space that are safe, welcoming and relevant to children and young people will impact on their overall wellbeing and may help to prevent many of the tensions occurring in Australia and elsewhere around the world. This area is the subject of ongoing international debate, research and policy formation, relevant to concerns in the ARACY Report Card about children and young people’s health and safety, participation, behaviours and risks and peer and family relationships.

Young people and the social exclusion of their public and private space

This paper explores the concept of social exclusion as it impacts on young people within their local communities and the wider British, European and Australian context in terms of surveillance and other control measures.

Young people, children and their social and spatial citizenship rights

The use of public space by young people and children is a major issue in a number of countries and a range of measures are deployed to to control public space which restrict their social and spatial citizenship rights.