JRSBRT 7.3, p. 213-221

The impact of unscheduled gaps and iso-centre sequencing on the biologically effective dose in Gamma knife radiosurgery
Thomas Klinge, Marc Modat, Jamie R. Mcclelland, Alexis Dimitriadis, Ian Paddick, John W. Hopewell, Lee Walton, Jeremy Rowe, Neil Kitchen and Sébastien Ourselin

Purpose: Establish the impact of iso-centre sequencing and unscheduled gaps in Gamma Knife® (GK) radiosurgery on the biologically effective dose (BED).

Methods: A BED model was used to study BED values on the prescription iso-surface of patients treated with GK Perfexion™ (Vestibular Schwannoma). The effect of a 15 min gap, simulated at varying points in the treatment delivery, and adjustments to the sequencing of iso-centre delivery, based on average dose-rate, was quantified in terms of the impact on BED.

Results: Depending on the position of the gap and the average dose-rate profiles, the mean BED values were decreased by 0.1% to 9.9% of the value in the original plan. A heuristic approach to iso-centre sequencing showed variations in BED of up to 14.2%, relative to the mean BED of the original sequence.

Conclusion: The treatment variables, like the iso-centre sequence and unscheduled gaps, should be considered during GK radiosurgery treatments.

Keywords: Biologically effective dose (BED), radiosurgery, iso-centre sequencing

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