PODSE: A computer program for optimal design of trials with discrete-time survival endpoints
Utrecht University, The Netherlands. Electronic address: .Computer methods and programs in biomedicine (Impact Factor: 1.9). 04/2013; 111(1). DOI: 10.1016/j.cmpb.2013.02.005
In experimental settings, one or more groups of subjects receive a treatment and they are compared to a group of subjects that receives a standard treatment or no treatment at all. These compared groups might have an equal number of subjects or some of the groups might have more participants relative to the other groups. Moreover, subjects in these groups can be followed over a short or a long period. To conduct experiments in a sufficient way, researchers should find a good design in the planning phase of the trial. The optimal design for experimental studies on event occurrence with discrete-time survival endpoints where two treatment groups are followed over time, is an optimal combination of the number of time periods, the total number of participants in the trial and the proportion of subjects in the experimental group. It is easy to find the best design for such studies using the PODSE program.
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ABSTRACT: The aim of event history analysis is to study the occurrence and timing of events, such as premature psychotherapy termination or drinking onset, and to relate the probability of event occurrence to relevant covariates. In the social sciences, the timing of the event is often measured discretely by using time intervals, which implies the exact timing of event occurrence is unknown. The optimal number of subjects and time intervals need to be decided upon in the design stage of a trial with discrete-time survival endpoints. This paper shows how the optimal design depends on the underlying survival function and the costs to include a subject relative to the costs to take a measurement. Furthermore, the effects of attrition on the optimal design are studied. An example on drinking onset illustrates the proposed methodology. (PsycINFO Database Record (c) 2014 APA, all rights reserved)Zeitschrift für Psychologie 01/2013; 221(3):160. DOI:10.1027/2151-2604/a000144 · 1.57 Impact Factor
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ABSTRACT: Purpose: The accuracy of dose delivery and the evaluation of differences between calculated and delivered dose distributions, has been studied by several groups. The aim of this investigation is to extend the gamma index by including radiobiological information and to propose a new index that we will here forth refer to as the gamma plus (γ+). Furthermore, to validate the robustness of this new index in performing a quality control analysis of an IMRT treatment plan using pure radiobiological measures such as the biologically effective uniform dose (D) and complication-free tumor control probability (P+). Material and methods: A new quality assurance index, the (γ+), is proposed based on the theoretical concept of gamma index presented by Low et al. (1998). In this study, the dose difference, including the radiobiological dose information (biological effective dose, BED) is used instead of just the physical dose difference when performing the γ+ calculation. An in-house software was developed to compare different dose distributions based on the γ+ concept. A test pattern for a two-dimensional dose comparison was built using the in-house software platform. The γ+ index was tested using planar dose distributions (exported from the treatment planning system) and delivered (film) dose distributions acquired in a solid water phantom using a test pattern and a theoretical clinical case. Furthermore, a lung cancer case for a patient treated with IMRT was also selected for the analysis. The respective planar dose distributions from the treatment plan and the film were compared based on the γ+ index and were evaluated using the radiobiological measures of P+ and D. Results: The results for the test pattern analysis indicate that the γ+ index distributions differ from those of the gamma index since the former considers radiobiological parameters that may affect treatment outcome. For the theoretical clinical case, it is observed that the γ+ index varies for different treatment parameters (e.g. dose per fraction). The dose area histogram (DAH) from the plan and film dose distributions are associated with P+ values of 50.8% and 49.0%, for a D to the target of 54.0 Gy and 53.3 Gy, respectively. Conclusion: The γ+ index shows advantageous properties in the quantitative evaluation of dose delivery and quality control of IMRT treatments because it includes information about the expected responses and radiobiological doses of the individual tissues.Computer methods and programs in biomedicine 04/2014; 114(1). DOI:10.1016/j.cmpb.2014.01.005 · 1.90 Impact Factor
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