• 대한방사선치료학회지
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• 제24권1호
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• pp.1-10
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• 2012

목 적: 동적다엽콜리메이터를 이용한 세기변조방사선 치료 시 선량률 임의 변경 되었을 경우 선량 분포 차와 변화를 평가하고자 한다. 대상 및 방법: 소조사야와 대조사야의 두 가지 세기변조방사선치료계획을 임상적 치료계획시스템(Eclipse, Varian, Palo Alto, CA)을 이용하여 계획하였다. 각각의 치료계획은 선량률 100, 400, 600 MU/min으로 변화시켜 조사야별 세 종류로 치료계획을 하였다. 측정기 2D-Array (2D-Array Seven729, PTW-Freiburg)는 측정 깊이 0.5 cm를 고려하여 위로 Solid water phantom ($30{\times}30{\times}4.5cm$)와 아래로 후방산란을 고려한 Solid water phantom 5 cm 사이에 위치 시켰다. MLC-120엽을 갖춘 에너지 6 MV 선형가속기(Clinac 21EX, Varian, Palo Alto, CA)를 사용하여 실험하였다. 첫 번째로 선량률 100, 400, 600 MU/min의 치료 계획한 것을 같은 선량률로 측정 하여 각각의 기준값을 얻었다. 1) 선량률 100 MU/min일 때 임의로 200, 300, 400, 500, 600 MU/min로 변화하고, 2) 400 MU/min일 때 100, 200, 300, 500, 600 MU/min으로 변화시켰으며, 3) 600 MU/min일 때 100, 200, 300, 400, 500 MU/min를 측정하였다. 끝으로 분석 프로그램(Verisoft 3.1, PTW-Freiburg)을 이용하여 기준 값과 선량률 변화 시의 선량차와 분포를 평가 하였다. 결 과: 치료 계획한 선량률 100 MU/min, 400 MU/min, 600 MU/min을 치료 계획한 대로 측정한 기준 값은 미세한 선량차를 보였고 선량분포도 일치하였다. 이를 기준 값으로 하여 소조사야에 대해 측정한 결과 100 MU/min에서는 200, 300, 400, 500, 600MU/min으로 변경하며 측정 시 -0.8, -1.1, -1.3, -1.5, -1.6%로 선량차가 있었으며, 400 MU/min (소조사야)에서 100, 200, 300, 500, 600 MU/min일 때 +0.9, +0.3, +0.1, -0.2, -0.2%의 선량변화가 있었고, 선량률 600 MU/min (소조사야)에서는 100, 200, 300, 400, 500 MU/min으로 변경 시 +1.4, +0.8, +0.5, +0.3, +0.2%로 나타났다. 다른 한편, 대조사야에서 100 MU/min(대조사야)는 -1.3, -1.6, -1.8, -2.0, -2.4%로 조금 더 큰 감소를 보였고, 400 MU/min (대조사야)는 +2.0, +1.8, +0.5, -1.2, -1.6%의 선량변화가 있었다. 600 MU/min (대조사야)에서는 +1.5, +1.9, +1.7, +1.9, +1.2%였다. 선량률 변화에 따른 선량 차는 -2.4~+2.0%로 측정되었다. 결 론: 120-MLC를 갖춘 선형가속기를 사용하여 측정한 세기변조방사선 치료 시 선량률 변화에 따른 선량분포는 거의 변화가 없었으며 선량 차는 ${\pm}3%$ 미만이었다.

• Asia pacific journal of information systems
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• 제20권2호
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• pp.63-86
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• 2010

Personalized services directly and indirectly acquire personal data, in part, to provide customers with higher-value services that are specifically context-relevant (such as place and time). Information technologies continue to mature and develop, providing greatly improved performance. Sensory networks and intelligent software can now obtain context data, and that is the cornerstone for providing personalized, context-specific services. Yet, the danger of overflowing personal information is increasing because the data retrieved by the sensors usually contains privacy information. Various technical characteristics of context-aware applications have more troubling implications for information privacy. In parallel with increasing use of context for service personalization, information privacy concerns have also increased such as an unrestricted availability of context information. Those privacy concerns are consistently regarded as a critical issue facing context-aware personalized service success. The entire field of information privacy is growing as an important area of research, with many new definitions and terminologies, because of a need for a better understanding of information privacy concepts. Especially, it requires that the factors of information privacy should be revised according to the characteristics of new technologies. However, previous information privacy factors of context-aware applications have at least two shortcomings. First, there has been little overview of the technology characteristics of context-aware computing. Existing studies have only focused on a small subset of the technical characteristics of context-aware computing. Therefore, there has not been a mutually exclusive set of factors that uniquely and completely describe information privacy on context-aware applications. Second, user survey has been widely used to identify factors of information privacy in most studies despite the limitation of users' knowledge and experiences about context-aware computing technology. To date, since context-aware services have not been widely deployed on a commercial scale yet, only very few people have prior experiences with context-aware personalized services. It is difficult to build users' knowledge about context-aware technology even by increasing their understanding in various ways: scenarios, pictures, flash animation, etc. Nevertheless, conducting a survey, assuming that the participants have sufficient experience or understanding about the technologies shown in the survey, may not be absolutely valid. Moreover, some surveys are based solely on simplifying and hence unrealistic assumptions (e.g., they only consider location information as a context data). A better understanding of information privacy concern in context-aware personalized services is highly needed. Hence, the purpose of this paper is to identify a generic set of factors for elemental information privacy concern in context-aware personalized services and to develop a rank-order list of information privacy concern factors. We consider overall technology characteristics to establish a mutually exclusive set of factors. A Delphi survey, a rigorous data collection method, was deployed to obtain a reliable opinion from the experts and to produce a rank-order list. It, therefore, lends itself well to obtaining a set of universal factors of information privacy concern and its priority. An international panel of researchers and practitioners who have the expertise in privacy and context-aware system fields were involved in our research. Delphi rounds formatting will faithfully follow the procedure for the Delphi study proposed by Okoli and Pawlowski. This will involve three general rounds: (1) brainstorming for important factors; (2) narrowing down the original list to the most important ones; and (3) ranking the list of important factors. For this round only, experts were treated as individuals, not panels. Adapted from Okoli and Pawlowski, we outlined the process of administrating the study. We performed three rounds. In the first and second rounds of the Delphi questionnaire, we gathered a set of exclusive factors for information privacy concern in context-aware personalized services. The respondents were asked to provide at least five main factors for the most appropriate understanding of the information privacy concern in the first round. To do so, some of the main factors found in the literature were presented to the participants. The second round of the questionnaire discussed the main factor provided in the first round, fleshed out with relevant sub-factors. Respondents were then requested to evaluate each sub factor's suitability against the corresponding main factors to determine the final sub-factors from the candidate factors. The sub-factors were found from the literature survey. Final factors selected by over 50% of experts. In the third round, a list of factors with corresponding questions was provided, and the respondents were requested to assess the importance of each main factor and its corresponding sub factors. Finally, we calculated the mean rank of each item to make a final result. While analyzing the data, we focused on group consensus rather than individual insistence. To do so, a concordance analysis, which measures the consistency of the experts' responses over successive rounds of the Delphi, was adopted during the survey process. As a result, experts reported that context data collection and high identifiable level of identical data are the most important factor in the main factors and sub factors, respectively. Additional important sub-factors included diverse types of context data collected, tracking and recording functionalities, and embedded and disappeared sensor devices. The average score of each factor is very useful for future context-aware personalized service development in the view of the information privacy. The final factors have the following differences comparing to those proposed in other studies. First, the concern factors differ from existing studies, which are based on privacy issues that may occur during the lifecycle of acquired user information. However, our study helped to clarify these sometimes vague issues by determining which privacy concern issues are viable based on specific technical characteristics in context-aware personalized services. Since a context-aware service differs in its technical characteristics compared to other services, we selected specific characteristics that had a higher potential to increase user's privacy concerns. Secondly, this study considered privacy issues in terms of service delivery and display that were almost overlooked in existing studies by introducing IPOS as the factor division. Lastly, in each factor, it correlated the level of importance with professionals' opinions as to what extent users have privacy concerns. The reason that it did not select the traditional method questionnaire at that time is that context-aware personalized service considered the absolute lack in understanding and experience of users with new technology. For understanding users' privacy concerns, professionals in the Delphi questionnaire process selected context data collection, tracking and recording, and sensory network as the most important factors among technological characteristics of context-aware personalized services. In the creation of a context-aware personalized services, this study demonstrates the importance and relevance of determining an optimal methodology, and which technologies and in what sequence are needed, to acquire what types of users' context information. Most studies focus on which services and systems should be provided and developed by utilizing context information on the supposition, along with the development of context-aware technology. However, the results in this study show that, in terms of users' privacy, it is necessary to pay greater attention to the activities that acquire context information. To inspect the results in the evaluation of sub factor, additional studies would be necessary for approaches on reducing users' privacy concerns toward technological characteristics such as highly identifiable level of identical data, diverse types of context data collected, tracking and recording functionality, embedded and disappearing sensor devices. The factor ranked the next highest level of importance after input is a context-aware service delivery that is related to output. The results show that delivery and display showing services to users in a context-aware personalized services toward the anywhere-anytime-any device concept have been regarded as even more important than in previous computing environment. Considering the concern factors to develop context aware personalized services will help to increase service success rate and hopefully user acceptance for those services. Our future work will be to adopt these factors for qualifying context aware service development projects such as u-city development projects in terms of service quality and hence user acceptance.