Author: Christopher S. Melhus, Elizabeth Meyer, Cassandra Stambaugh 👨🔬
Affiliation: Tufts Medical Center 🌍
Purpose: To investigate the clinical treatment planning parameters that impact patient-specific quality assurance (PSQA) passing rates for hippocampal avoidance whole brain (HAWB) treatment plans.
Methods: Four HAWB plans previously created using autoplanning and a 2 arc, 6 MV, split-field technique were identified; two passed and two failed initial PSQA. These plans were analyzed with Sun Nuclear Corp (Melbourne, FL) software for feasibility (PlanIQ), 3D calculated (DoseCHECK), and array/3D measured dose comparison (SNC Patient/3DVH). Based on the results, one failing plan was replanned using: increased margin around the hippocampus, increased field overlap, and decreased modulation. Each was reanalyzed to determine if the planning adjustments increased agreement between the treatment planning system (TPS) estimate and the machine delivery.
Results: Analysis revealed a range of goals for the hippocampus (Max 0.03 cc <15-21 Gy) and low goal feasibility (0.00-0.11) without compromising target coverage. Failing plans showed poorer agreement between DoseCHECK and the TPS, with average difference in D95%=-1.72% for the target compared to -1.13% for passing plans. Measured hippocampal and target volume passing rates were below institutional ROI standards of >90% (3%/2mm) in 3DVH. Failing plans had smaller hippocampal margins and field overlap, and more modulation; therefore, these parameters were adjusted for replanning. Additionally, a maximum hippocampal dose of 17 Gy and target dose of D2%<37.5 was used. The three replans showed improved feasibility and better agreement in SNC Patient (+2.1%, +2.8%, +3.1% for adjustments of margin, field overlap, and modulation). Agreement with DoseCHECK and TPS target dose also improved (average 98.7% from 94.1%, 2%/2mm)
Conclusion: This case study underscores the importance of optimizing planning parameters, such as planning goals, hippocampal margin, field overlap, and modulation, to improve PSQA passing rates for HAWB plans while ensuring effective hippocampal sparing. Carefully adjusting these parameters may enhance the quality and accuracy of highly modulated plans.