• World Neurosurg · Apr 2023

    Improving the accuracy of biologically effective dose (BED) estimates, from a previously published study, after radiosurgery for acoustic neuromas.

    • John W Hopewell, Joshua Moore, Conrad J Villafuerte, Ian Paddick, Bleddyn Jones, Mark A Hill, and Derek S Tsang.
    • Green Templeton College, University of Oxford, Oxford, UK; Department of Oncology, University of Oxford, Oxford, UK. Electronic address: john.hopewell@gtc.ox.ac.uk.
    • World Neurosurg. 2023 Apr 1; 172: e130e143e130-e143.

    ObjectiveTo recalculate biological effective dose values (BED) for radio-surgical treatments of acoustic neuroma from a previous study. BEDs values were previously overestimated by only using beam-on times in calculations, so excluding the important beam-off-times (when deoxyribonucleic acid repair continues) which contribute to the overall treatment time. Simple BED estimations using a mono-exponential approximation may not always be appropriate but if used should include overall treatment time.MethodsTime intervals between isocenters were estimated. These were especially important for the Gamma Knife Model 4C cases since manual changes significantly increase overall treatment times. Individual treatment parameters, such as iso-center number, beam-on-time, and beam-off-time, were then used to calculate BED values using a more appropriate bi-exponential model that includes fast and slow components of DNA damage repair over a wider time range.ResultsThe revised BED estimates differed significantly from previously published values. The overestimates of BED, obtained using beam-on-time only, varied from 0%-40.3%. BED subclasses, each with a BED range of 5 Gy2.47, indicated that revised values were consistently reduced when compared with originally quoted values, especially for 4C compared with Perfexion cases. Furthermore, subdivision of 4C cases by collimator number further emphasized the impact of scheduled gap times on BED. Further analysis demonstrated important limitations of the mono-exponential model. Target volume was a major confounding factor in the interpretation of the results of this study.ConclusionsBED values should be estimated by including beam-on and beam-off times. Suggestions are provided for more accurate BED estimations in future studies.Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.

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