Systematic evaluation and plan quality assessment of the Leksell® gamma knife® lightning dose optimizer

Abstract

To compare stereotactic radiosurgery (SRS) plan quality metrics of manual forward planning (MFP) and Elekta Fast Inverse Planning TM (FIP)-based inversely optimized plans for patients treated with Gamma Knife®. Clinically treated, MFP SRS plans for 100 consecutive patients (115 lesions; 67 metastatic and 48 benign) were replanned with the FIP dose optimizer based on a convex linear programming formulation. Comparative plans were generated to match or exceed the following metrics in order of importance: Target Coverage (TC), Paddick Conformity Index (PCI), beam-on time (BOT), and Gradient Index (GI). Plan quality metrics and delivery parameters between MFP and FIP were compared for all lesions and stratified into subgroups for further analysis. Additionally, performance of FIP for multiple punctate ( < 4 mm) metastatic lesions on a subset of cases was investigated. A Wilcoxon signed-rank test for non-normal distributions was used to assess the statistical differences between the MFP and FIP treatment plans. Overall, 76% (87/115) of FIP plans showed a statistically significant improvement in plan quality compared to MFP plans. As compared to MFP, FIP plans demonstrated an increase in the median PCI by 1.1% ( p < 0.01), a decrease in GI by 3.7% ( p < 0.01), and an increase in median number of shots by 74% ( p < 0.01). TC and BOT were not statistically significantly different between MFP and FIP plans ( p > 0.05). FIP plans showed a statistically significant increase in use of 16 mm ( p < 0.01) and blocked shots ( p < 0.01), with a corresponding decrease in 4 mm shots ( p < 0.01). Use of multiple shots per coordinate was significantly higher in FIP plans ( p < 0.01). The FIP optimizer failed to generate a clinically acceptable plan in 4/115 (3.5%) lesions despite optimization parameter changes. The mean optimization time for FIP plans was 5.0 min (Range: 1.0 -10.0 min). In the setting of multiple punctate lesions, PCI for FIP was significantly improved ( p < 0.01) by changing the default low-dose/BOT penalty optimization setting from a default of 50/50 to 75-85/40. FIP offers a significant reduction in manual effort for SRS treatment planning while achieving comparable plan quality to an expert planner-substantially improving overall planning efficiency. FIP plans employ a non-intuitive increased use of blocked sectors and shot-in-shot technique to achieve high quality plans. Several FIP plans failed to achieve clinically acceptable treatments and warrant further investigation.

Clinical Evaluation of the Inverse Planning System Utilized in Gamma Knife Lightning

“…Wieczorek et al. ( 11 ) compared inverse plans optimized by GK Lightning with manual forward plans on 115 lesions and demonstrated that the inverse plans were comparable or superior to forward plans with regard to plan quality metrics. Spaniol et al.…”

“…More recently, a new inverse planning technology has become clinically available in the latest GK Lightning TPS which enables an automatic workflow for GK treatment planning with minimum manual inputs ( 10 ). While the initial study performed by the vendor has demonstrated encouraging results, only two independent studies on GK Lightning have been recently published ( 11 , 12 ), and independent evaluations of the inverse planning technology with broader clinical relevance are still in need. In the current manuscript, we aim to evaluate this new inverse planning technology by comparing the inversely optimized plan generated with this technology to clinically approved forward-based plans for a variety of disease types.…”

OptImal Gamma kNife lIghTnIng sOlutioN (IGNITION) score to characterize the solution space of the Gamma Knife FIP optimizer for stereotactic radiosurgery

“…In our previous study, we showed that the FIP optimizer was shown to significantly reduce the efforts for treatment planning while achieving comparable plan quality of an expert planner 12 . The FIP treatment plans were generated at a default optimization setting of 0.5/0.5 (Range: 0–1) followed by minor tweaks to the plan to achieve a target coverage of 100% and minimize PCI.…”

Clinical validation of novel lightning dose optimizer for gamma knife radiosurgery of irregular‐shaped arteriovenous malformations and pituitary adenomas

“…In contrast to this offline planning software, LDO is implemented in the GammaPlan platform, hence, is much more time efficient. At the time of this manuscript preparation, Wieczorek and colleagues 20 published a paper in the Medical Dosimetry Journal showing the plan quality metrices of the Leksell GK LDO for multiple sites of the brain disease, including AVM's. They have reported the target coverage, conformity, GI, number of shots, and beam‐on time; however, no dose to normal brain and dose to critical organs were presented.…”