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gamma(+) index: A new evaluation parameter for quantitative quality assurance
Stockholm University, Faculty of Science, Department of Physics. Karolinska Institute, Sweden.
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2014 (English)In: Computer Methods and Programs in Biomedicine, ISSN 0169-2607, E-ISSN 1872-7565, Vol. 114, no 1Article in journal (Refereed) Published
Abstract [en]

Purpose: The accuracy 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 (gamma(+)). Further more, 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) over bar) and complication-free tumor control probability (P+). Material and methods: A new quality assurance index, the (gamma(+)), 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 gamma(+) calculation. An in-house software was developed to compare different dose distributions based on the gamma(+) concept. A test pattern for a two-dimensional dose comparison was built using the in-house software platform. The gamma(+) 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 gamma(+) index and were evaluated using the radiobiological measures of P+ and (D) over bar. Results: The results for the test pattern analysis indicate that the gamma(+) 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 gamma(+) 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) over bar to the target of 54.0 Gy and 53.3 Gy, respectively. Conclusion: The gamma(+) 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.

Place, publisher, year, edition, pages
2014. Vol. 114, no 1
Keyword [en]
Gamma index, gamma(+) index, Quality assurance, IMRT
National Category
Physical Sciences
URN: urn:nbn:se:su:diva-102947DOI: 10.1016/j.cmpb.2014.01.005ISI: 000332528900006OAI: diva2:715031


Available from: 2014-04-30 Created: 2014-04-25 Last updated: 2014-04-30Bibliographically approved

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Mavroidis, Panayiotis
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