Performance Evaluation Of The Extend™ Relocatable Head Frame For Linac And Perfexion™ Intra-cranial Stereotactic RadiotherapyMark Ruschin1, Nazanin Nayebi2, Per Carlsson3, Kevin Brown3, Messeret Tamerou2, Winnie Li2, Young-Bin Cho2, Cynthia Ménard2, David Jaffray21Toronto, Canada 2Princess Margaret Hospital 3 Elekta SA Keywords: Extend, radiotherapy, gamma knife, stereotactic frame, Fractionated radiosurgeryInteractive ManuscriptAsk Questions of this Manuscript: What is the background behind your study? What is the purpose of your study?The purpose of this study is to evaluate the geometric positioning and immobilization performance of the relocatable head frame (RHF) system from eXtend™ for linac and Perfexion™ (PFX) stereotactic radiotherapy (SRT). Describe your patient group.Fourteen patients prospectively enrolled on a clinical trial received image-guided linac based SRT using the RHF for setup and immobilization. A second cohort are currently enrolled on a phase 1 dose escalation clinical trial investigating hypofractionated and adaptive PFX stereotactic radiotherapy (SRT) for large brain metastases; where a treatment plan is generated for each fraction based on repeat CT and MRI one day prior. Describe what you did.The linac patients received a median number of 30 daily treatment fractions whereas the PFX patients receive 3 fractions of radiation over 21 days. Daily positional displacements are determined using a repositioning check tool (RCT), which acts like a depth-helmet. For the linac patients, where the RCT-reported displacement was <1mm (action level) offline-CBCT was used to quantify positioning and immobilization (intra-fraction) displacement in stereotactic coordinates. For the PFX patients, the RCT yields positioning displacement in stereotactic coordinates directly. Describe your main findings.The mean 3D positioning displacement was 1.3mm, with an inter-patient and inter-fraction variation (1 SD) of 0.9mm and 0.4mm respectively. The mean 3D intra-fraction motion was 0.4mm. The group mean setup displacement was {0.3mm;-0.5mm;-0.7mm} along {Right; Superior; Anterior}. For two patients treated to date on PFX, the mean difference between CT-planning position and PFX position was {0.2mm;-0.9mm;-0.8mm}. These results indicated that for both the linac and PFX cohort, patients tended to be setup within the RHF inferiorly and posteriorly compared to CT. The mean difference between successive PFX positions and between successive CT positions was {0.1mm; 0.3mm; 0.2mm} and {0.1mm; 0.0mm; 0.0mm} respectively. The larger setup uncertainty observed between CT and PFX may be due to differences in couch types or RHF components used at CT versus PFX. Describe the main limitation of this study.This is a retrospective study. Describe your main conclusion.While the RHF provides excellent immobilization, a mean and patient-to-patient variation of 1.3mm and 0.9mm, respectively, in 3D positioning has been measured and must be considered when designing treatment plans. Describe the importance of your findings and how they can be used by others.Systematic treatment setup displacements in the inferior and posterior directions were observed for linac and PFX. The purpose of this study is to evaluate the geometric positioning and immobilization performance of the relocatable head frame (RHF) system from eXtend™ for linac and Perfexion™ (PFX) stereotactic radiotherapy (SRT). Fourteen patients prospectively enrolled on a clinical trial received image-guided linac based SRT using the RHF for setup and immobilization. A second cohort are currently enrolled on a phase 1 dose escalation clinical trial investigating hypofractionated and adaptive PFX stereotactic radiotherapy (SRT) for large brain metastases; where a treatment plan is generated for each fraction based on repeat CT and MRI one day prior. The linac patients received a median number of 30 daily treatment fractions whereas the PFX patients receive 3 fractions of radiation over 21 days. Daily positional displacements are determined using a repositioning check tool (RCT), which acts like a depth-helmet. For the linac patients, where the RCT-reported displacement was <1mm (action level) offline-CBCT was used to quantify positioning and immobilization (intra-fraction) displacement in stereotactic coordinates. For the PFX patients, the RCT yields positioning displacement in stereotactic coordinates directly. The mean 3D positioning displacement was 1.3mm, with an inter-patient and inter-fraction variation (1 SD) of 0.9mm and 0.4mm respectively. The mean 3D intra-fraction motion was 0.4mm. The group mean setup displacement was {0.3mm;-0.5mm;-0.7mm} along {Right; Superior; Anterior}. For two patients treated to date on PFX, the mean difference between CT-planning position and PFX position was {0.2mm;-0.9mm;-0.8mm}. These results indicated that for both the linac and PFX cohort, patients tended to be setup within the RHF inferiorly and posteriorly compared to CT. The mean difference between successive PFX positions and between successive CT positions was {0.1mm; 0.3mm; 0.2mm} and {0.1mm; 0.0mm; 0.0mm} respectively. The larger setup uncertainty observed between CT and PFX may be due to differences in couch types or RHF components used at CT versus PFX. This is a retrospective study. While the RHF provides excellent immobilization, a mean and patient-to-patient variation of 1.3mm and 0.9mm, respectively, in 3D positioning has been measured and must be considered when designing treatment plans. Systematic treatment setup displacements in the inferior and posterior directions were observed for linac and PFX. Project Roles:
M. Ruschin (), N. Nayebi (), P. Carlsson (), K. Brown (), M. Tamerou (), W. Li (), Y. Cho (), C. Ménard (), D. Jaffray ()
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