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

Abstract

ObjectivesThe purpose of this study is to independently compare the performance of the inverse planning algorithm utilized in Gamma Knife (GK) Lightning Treatment Planning System (TPS) to manual forward planning, between experienced and inexperienced users, for different types of targets.Materials and MethodsForty patients treated with GK stereotactic radiosurgery (SRS) for pituitary adenoma (PA), vestibular schwannoma (VS), post-operative brain metastases (pBM), and intact brain metastases (iBM) were randomly selected, ten for each site. Three inversely optimized plans were generated for each case by two experienced planners (OptExp1 and OptExp2) and a novice planner (OptNov) using GK Lightning TPS. For each treatment site, the Gradient Index (GI), the Paddick Conformity Index (PCI), the prescription percentage, the scaled beam-on time (sBOT), the number of shots used, and dosimetric metrics to OARs were compared first between the inversely optimized plans and the manually generated clinical plans, and then among the inversely optimized plans. Statistical analyses were performed using the Student’s t-test and the ANOVA followed by the post-hoc Tukey tests.ResultsThe GI for the inversely optimized plans significantly outperformed the clinical plans for all sites. PCIs were similar between the inversely optimized and clinical plans for PA and VS, but were significantly improved in the inversely optimized plans for iBM and pBM. There were no significant differences in the sBOT between the inversely optimized and clinical plans, except for the PA cases. No significant differences were observed in dosimetric metrics, except for lower brain V12Gy and PTV D98% in the inversely optimized plans for iBM. There were no noticeable differences in plan qualities among the inversely optimized plans created by the novice and experienced planners.ConclusionInverse planning in GK Lightning TPS produces GK SRS plans at least equivalent in plan quality and similar in sBOT compared to manual forward planning in this independent validation study. The automatic workflow of inversed planning ensures a consistent plan quality regardless of a planner’s experience.

A study on inter‐planner plan quality variability using a manual planning‐ or Lightning dose optimizer‐approach for single brain lesions treated with the Gamma Knife® Icon™

“…In this study, FIP plans achieved lower GI than MFP plans for all three groups except MFP plans generated by the Senior for the BM intact (Figure 2[d-f]). This result is consistent with the findings of Spaniol et al, Wieczorek et al, and Cui et al 5,8,9 The FIP optimizer tends to use various combinations of the collimators. 8,9 The FIP optimizer optimizes such that shots are well distributed, shots have various beam shapes by combinations of the collimators and notably, multiple shots with different beam shapes are placed at the same isocenter (reusing isocenter) to achieve high PCI, low GI, and short BOT for lesions.…”

“…5 Cui et al concluded that the FIP optimizer produced equivalent plans with similar BOT compared with clinical MFP plans. 9 Their findings are similar to our findings demonstrating that all three planners' FIP plans are comparable or superior to the clinical plans. Due to planners' experience level, however, in this study, Senior, Junior, and Novice's MFP plans were superior, comparable, and inferior to the clinical plans, respectively.…”

“…8 In each GK shot, the radiation is delivered for a specified time at an isocenter position with a given collimator configuration composed of various sector settings. 1,9 Traditionally, GK planning has been performed in a manual planning approach. In this approach, the planner manually places shots within the target and iteratively adjusts their locations, collimator configurations, and relative weights.…”

“…8 There are a few published studies including the vendor's initial study comparatively evaluating FIP (Lightning) versus clinical manual planning for selected brain lesions. 1,5,8,9 However, Sjölund et al and Wieczorek et al did not investigate inter-planner variability when employing FIP. 1,8 Cui et al included three planners for FIP plans but their study was primarily focused on the comparison between FIP and clinical manual planning.…”

“…1,8 Cui et al included three planners for FIP plans but their study was primarily focused on the comparison between FIP and clinical manual planning. 9 Spaniol et al assessed inter-planner variability in both manual planning and FIP, but planning was performed by three experienced planners and the variability among the planners was evaluated only for three patients with different diagnosis. 5 Moreover, none of the studies were "real-world", in other words, limiting planning time, which is a necessity in clinical practice.…”