Author: Alyssa Gadsby, William J. Godwin, Daniel G. McDonald, Jean L. Peng, Alek K. Rapchak, Sean A Roles, Austin M. Skinner, Stephanie Tan 👨🔬
Affiliation: Medical University of South Carolina 🌍
Purpose:
This study evaluates optimization strategies in the Gamma Knife Gamma Plan Lightning optimizer for simultaneous integrated boost (SIB) scenarios, aiming to identify clinically viable settings and provide planning recommendations.
Methods:
A nonspherical deep-seated target (primary) and an offset subvolume (boost) were contoured. Eleven plans delivering 14 Gy to the primary and 22 Gy to the boost were generated, varying strategies: simultaneous or sequential optimization with different priorities for low dose, beam-on time, and coverage. Plans were assessed using Paddick conformity index (PCI), selectivity, gradient index, coverage, and beam-on time. A blinded planner reviewed clinical viability and suitability for forward planning.
Three clinically viable plans were generated: FT1, FT2, and S50. FT1 optimized both targets with 0.5 low dose, 0.65 beam-on time, boost coverage selected, and minimized boost maximum dose. FT2 reoptimized FT1, focusing on the boost only with 0.65 low dose, 0.5 beam-on time, coverage selected, and minimized maximum dose. S50 used 0.5 weighting for low dose and beam-on time, no maximum dose, and unselected nominal coverage, targeting both volumes simultaneously.
Results:
Simultaneous optimization with optional boost reoptimization produced the most viable plans, minimizing post-optimization adjustments. Sequential optimizations with nonsimultaneous initial optimization or prioritizing low dose (1.0) and beam-on time (0.0) led to under-coverage and excessive treatment times. The viable plans (S50, FT1, FT2) achieved primary and boost coverage ≥0.99, PCI up to 0.58, and favorable beam-on times. FT1 reduced beam-on time by 30.2% versus S50. The blinded planner rated these 3 plans as the only viable options, favoring FT2 for forward planning and clinical use.
Conclusion:
Simultaneous optimization with optional boost reoptimization is recommended for SIB scenarios. Sequential optimization often results in suboptimal plans requiring renormalization or replanning. Strategies should balance coverage, PCI, gradient index, and beam-on time for clinically feasible results.