Real-world intrafraction motion assessment of Stereotactic Radiosurgery using HyperArcTM
PO-2254
Abstract
Real-world intrafraction motion assessment of Stereotactic Radiosurgery using HyperArcTM
Authors: Laura Barry1, Erica Bennett1, Theresa O'Donovan2, Paul Kelly1
1Bon Secours Radiotherapy Cork in partnership with UPMC Hillman Cancer Centre, Radiotherapy, Cork, Ireland; 2University College Cork, Radiation Therapy, School of Medicine, Cork, Ireland
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Purpose or Objective
• To quantify the intrafraction motion (IFM) for patients receiving HyperArcTM Stereotactic Radiosurgery (SRS)
• To determine whether treatment verification imaging using post-treatment cone-beam computed tomography (CBCT) can be safely omitted
Material and Methods
A retrospective analysis of isocentre displacements documented at each treatment fraction was conducted. Matched pre- and post-treatment CBCT was compared to determine the magnitude of IFM recorded in 6 degrees of freedom. The margins to compensate for IFM were calculated using the van Herk margin formula.
Results
19 patients comprising 65 fractions were analysed. The median number of SRS fractions per patient was 3 [range 3-5]. The most common dose fractionation was 27Gy in 3 fractions using HyperArcTM plans with 3-4 non-coplanar arcs on a Varian Edge Linear Accelerator. The mean residual error was 0.02mm (SD:0.02) (range -0.03 - 0.07) in anterior-posterior direction, 0.02mm (SD:0.04) (range:-0.07 - 0.09) in superior-inferior direction and 0.02mm (SD:0.03) (range:-0.11-0.07) in left-right direction. The mean pitch, roll and rotation residual errors were 0.24° (SD: 0.36) (range -0.6 -1.4), 0.20° (SD: 0.24) (range -0.3-1.1) and 0.21° (SD:0.27) (range -0.4 – 1.2) respectively. The margin compensation for IFM was less than 1 mm for the QFix EncompassTM immobilisation device.
Conclusion
Sub-millimetre accuracy was confirmed for the QFix EncompassTM immobilisation device during Stereotactic Radiosurgery using HyperArcTM. Post-treatment CBCT is now being eliminated after fraction one during multifraction HyperArcTM SRS treatment deliveries. A detailed analysis of the data to identify trends in patient demographics (ECOG, BMI, Age, Sex, Number of Lesions) and treatment related factors such as treatment time is warranted.