Improving the Accuracy of Biologically Effective Dose 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; Derek S Tsang

doi:10.1016/j.wneu.2022.12.119

Improving the Accuracy of Biologically Effective Dose Estimates, from a Previously Published Study, After Radiosurgery for Acoustic Neuromas

World Neurosurg. 2023 Apr:172:e130-e143. doi: 10.1016/j.wneu.2022.12.119. Epub 2022 Dec 29.

Authors

John W Hopewell¹, Joshua Moore², Conrad J Villafuerte³, Ian Paddick⁴, Bleddyn Jones⁵, Mark A Hill⁶, Derek S Tsang⁷

Affiliations

¹ Green Templeton College, University of Oxford, Oxford, UK; Department of Oncology, University of Oxford, Oxford, UK. Electronic address: john.hopewell@gtc.ox.ac.uk.
² School of Mathematics, Cardiff University, Cardiff, UK.
³ Radiation Oncology Department, The Medical City, Pasig City, Philippines.
⁴ Queen Square Gamma Knife Centre, National Hospital for Neurology and Neurosurgery, London, UK.
⁵ Green Templeton College, University of Oxford, Oxford, UK; Department of Oncology, University of Oxford, Oxford, UK.
⁶ Department of Oncology, University of Oxford, Oxford, UK.
⁷ Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada.

PMID: 36587897
DOI: 10.1016/j.wneu.2022.12.119

Abstract

Objective: To 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.

Methods: Time 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.

Results: The 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 Gy_2.47, 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.

Conclusions: BED values should be estimated by including beam-on and beam-off times. Suggestions are provided for more accurate BED estimations in future studies.

Keywords: Acoustic neuroma; Biologically effective dose; Brain oedema; Radiation volume related effects; Radiosurgery; Vestibular schwannoma.

MeSH terms

Humans
Neuroma, Acoustic* / radiotherapy
Neuroma, Acoustic* / surgery
Radiosurgery* / methods
Radiotherapy Dosage