Abstract
PurposeThe aim of this study was to provide a comprehensive assessment of patient intrafraction motion in linac‐based frameless stereotactic radiosurgery (SRS) and radiotherapy (SRT).MethodsA retrospective review was performed on 101 intracranial SRS/SRT patients immobilized with the Klarity stereotactic thermoplastic mask (compatible with the Brainlab frameless stereotactic system) and aligned on a 6 Degree of Freedom (DoF) couch with the Brainlab ExacTrac image guidance system. Both pretreatment and intrafraction correction data are provided as observed by the ExacTrac system. The effects of couch angle and treatment duration on positioning outcomes are also explored.ResultsInitial setup data for patients is shown to vary by up to ±4.18 mm, ±2.97°, but when corrected with a single x‐ray image set with ExacTrac, patient positions are corrected to within ±2.11 mm, ±2.27°. Intrafraction patient motion is shown to be uniformly random and independent of both time and couch angle. Patient motion was also limited to within approximately 3 mm, 3° by the thermoplastic mask.ConclusionsOur results indicate that since patient intrafraction motion is unrelated to couch rotation and treatment duration, intrafraction patient monitoring in 6 DoF is required to minimize intracranial SRS/SRT margins.
Highlights
Our analysis of patient positioning for intracranial stereotactic radiosurgery (SRS) treatments is divided into three components: (a) patient setup, (b) patient intrafraction motion, and (c) the effects of treatment times on patient positioning
The largest bias is observed in the vertical translations whereby the mean value is −1.03 mm
We propose that IR monitoring of the mask has significant limitations in situations where single isocenters are employed for multiple metastases, as the IR system only registers the patient position in 3 Degree of Freedom (DoF) and will not account for any rotation discrepancies
Summary
The aim of this study was to provide a comprehensive assessment of patient intrafraction motion in linac‐based frameless stereotactic radiosurgery (SRS) and radiotherapy (SRT)
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