Plenary Oral Presentations - Macquarie University Hospital

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16 th International Meeting of the Leksell Gamma Knife ® SocietyMarch 2012, Sydney, AustraliaPH-191Inter- and intra-fraction performance of the Gamma KnifeExtend System for patient positioning and immobilizationDavid Schlesinger, Chun-Po Yen, Zhiyuan Xu, Jason Sheehan<strong>University</strong> of VirginiaObjective: The Gamma Knife Extend System makes possible multi-fraction Gamma Knife treatments.The Extend System consists of a vacuum-monitored immobilization frame and a positioning measurementsystem to determine the location of the patient’s head within the frame at the time of simulationimaging and before each treatment fraction. The measurement system consists of a RepositioningCheck Tool (RCT) that attaches to the Extend frame, and associated digital measuring gauges. Thepurpose of this study is to evaluate the pre-fraction repositioning and intra-fraction immobilizationperformance of the Extend System for the first ten patients (n=36 fractions) treated at the <strong>University</strong>of Virginia.Methods: For each patient, the RCT was used to acquire a set of reference measurements of thepatient’s position at the time of CT simulation. Before each fraction repositioning measurements wereacquired, and the patient position was adjusted until the residual radial difference from the referenceposition measurements were less than 1mm (if possible). After treatment, position measurements wereacquired and the difference from the pre-fraction position was calculated as a measure of immobilizationcapability.Analysis of patient setup and immobilization performance included calculation of group mean, standarddeviation (SD), and distribution of systematic (components affecting all fractions) and random(per-fraction) uncertainty components.Results: Across all patients and fractions, the achieved mean radial setup difference from the referencemeasurements was 0.65mm, SD=0.24mm. The distribution of systematic uncertainty was 0.17mm.The distribution of random uncertainty was 0.16mm. The RMS differences for each plate wereright=0.35mm; left=0.41mm; superior=0.28mm; anterior=0.20mm.The mean intrafractional positional difference across all treatments was 0.46mm, SD=0.30mm. Thedistribution of systematic uncertainty was 0.19mm. The distribution of random uncertainty was0.22mm. One treatment fraction was excluded from the analysis because the vacuum monitoringinterlock detected patient motion, requiring mid-fraction repositioning.Conclusions: With appropriate patient selection, the Extend system can be used to reposition patientswith sub-millimeter precision, and appears to have adequate immobilization capability. However, careshould be taken to acquire measurements that can implicitly account for rotations of the patient’shead. Further work is required to determine the sensitivity of the vacuum interlock to detect patientmotion.60
16 th International Meeting of the Leksell Gamma Knife ® SocietyMarch 2012, Sydney, AustraliaPH-199Comparison of radiosurgical treatment parameters betweenthe Perfexion and previous Gamma Knife modelYong-Seok Im, Kwang-Mook Park, Jung-Il LeeDepartment of Neurosurgery, Samsung Medical Center, Seoul, KoreaObjective: We compared radiosurgical treatment parameters between the Leksell Gamma Knife(LGK)Perfexion(PFX) and previous models(LGK B/C).Methods: At our center, 495 patients were treated with the LGK B(Jan. 2002 – Feb. 2004). 3,102patients were treated with the LGK C(Mar. 2004 – May 2010). 803 patients were treated with thePFX(Jun. 2010 – Jul. 2011). Treatment parameters were evaluated and compared by measuring thegradient index(GI), conformity index(CI), Paddick conformity index(PCI), selectivity index(SI), beamon time(BT), treatment time, treatment position type, and collision risk.Analysis of patient setup and immobilization performance included calculation of group mean,standard deviation (SD), and distribution of systematic (components affecting all fractions) andrandom (per-fraction) uncertainty components.Results: In the similar dose rate (range 3.1~3.4Gy/min), the median total time in the treatmentroom per patient was 56min (BT=53min) for PFX, 77min (BT=40min) for LGK C(C), and 96min(BT=35min) for LGK B(B). In the whole population, The collision check was predicted byGammaPlan for at least one shot in 5.4% of the patients treated with PFX and in 58.8% of thepatients treated with C. The collision risk requiring technical adjustment(lateral position mode) wasobserved in 4.9% of the patients treated with C, and 2.4% of the patients treated with B. Technicalfailures for at least one shot occurred in 0.4% of the patients with PFX, 1.0% of the patients with C,and 1.0% of the patients with B. In vestibular schwannoma, the median values of GI in PFX, C andB were 2.65, 2.75 and 2.68, respectively. The CI in PFX, C and B were 1.17, 1.32 and 1.25. The PCIin PFX, C and B were 0.79, 0.73 and 0.76. The SI in PFX, C and B were 0.83, 0.75 and 0.78. Thecoverage and conformity indices were similar with both units.Conclusions: LGK PFX proved a high efficiency in treatment delivery by comparison with previousmodels. The clinical setting time and the QA procedure were reduced by the PFX.61
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Plenary Oral Presentations - Macquarie University Hospital

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