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Abstract
Purpose: The purpose of this study is to investigate inter-planner plan quality variability using a manual forward planning (MFP)- or fast inverse planning (FIP, Lightning)-approach for single brain lesions treated with the Gamma Knife® (GK) Icon™.

Methods: Thirty patients who were previously treated with GK stereotactic radiosurgery or radiotherapy were selected and divided into three groups (post-operative resection cavity, intact brain metastasis, and vestibular schwannoma [10 patients per group]). Clinical plans for the 30 patients were generated by multiple planners using FIP only (1), a combination of FIP and MFP (12), and MFP only (17). Three planners (Senior, Junior, and Novice) with varying experience levels re-planned the 30 patients using MFP and FIP (two plans per patient) with planning time limit of 60 min. Statistical analysis was performed to compare plan quality metrics (Paddick conformity index, gradient index, number of shots, prescription isodose line, target coverage, beam-on-time (BOT), and organs-at-risk doses) of MFP or FIP plans among three planners and to compare plan quality metrics between each planner's MFP/FIP plans and clinical plans. Variability in FIP parameter settings (BOT, low dose, and target max dose) and in planning time among the planners was also evaluated.

Results: Variations in plan quality metrics of FIP plans among three planners were smaller than those of MFP plans for all three groups. Junior's MFP plans were the most comparable to the clinical plans, whereas Senior's and Novice's MFP plans were superior and inferior, respectively. All three planners' FIP plans were comparable or superior to the clinical plans. Differences in FIP parameter settings among the planners were observed. Planning time was shorter and variations in planning time among the planners were smaller for FIP plans in all three groups.

Conclusions: The FIP approach is less planner dependent and more time-honored than the MFP approach.

Affiliations

Yongsook C Lee 1 2, D Jay Wieczorek 1 2, Vibha Chaswal 1 2, Rupesh Kotecha 1 2 3, Matthew D Hall 1 2, Martin C Tom 1 2, Minesh P Mehta 1 2, Michael W McDermott 3 4, Alonso N Gutierrez 1 2, Ranjini Tolakanahalli 1 2
1Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, USA.
2Department of Radiation Oncology, Herbert Wertheim College of Medicine, Florida International University, Miami, USA.
3Department of Translational Medicine, Herbert Wertheim College of Medicine, Florida International University, Miami, USA.
4Department of Neurosurgery, Miami Neuroscience Institute, Baptist Health South Florida, Miami, USA.