Author: Michael Evan Chaga, Timothy Chen, Darra M. Conti, Shabbar Danish, Jing Feng, Wenzheng Feng, Joseph Hanley, Tingyu Wang 👨🔬
Affiliation: Hackensack Meridian Health, Jersey Shore University Medical Center 🌍
Purpose: Using mixed fractionation schemes is a common technique in treating CNS lesions. This article describes an innovative plan-and-split approach for more efficient planning on the ZAP-X and thus providing new clinical opportunities.
Methods: In this course, two targets, PTV1 and PTV2 are prescribed to 22 Gy in 1 fraction and to 24 Gy in 3 fractions, respectively. Traditionally, two individual plans (Plan_A, Plan_B) are made with distinctive fractionation as normal on each target. In the new method, both targets are first optimized in one single plan (Plan_C) using 3 fractions to their prescribed doses. Plan_C uses the same isocenters used in Plan_A and Plan_B for the two targets. After optimization, isocenters with new beams/MUs on them are split back into groups with their associated targets to make individual plans (Plan_C_PTV1, Plan_C_PTV2) with proper fractionation. Each plan then is only re-prescribed to any isodose level to scale the dose to achieve 99% coverage on respective targets. No beam reduction would occur during the process. After each of the four individual plans achieved 99% dose coverage, two plan sums (Plan_A+Plan_B and Plan_C_PTV1+Plan_C_PTV2) representing the two planning approaches are compared on clinical objectives using Timmerman 2021 dose constraints. Dosimetric differences are analyzed using one tailed paired t-test for statistical significance (P < 0.05).
Results: Dose statistics across all organs and targets in the plan sum of the split plans show no statistically significant differences to the plan sum of the individually-optimized plans. Each individual plans made for each target are comparable to each other. Planning time is saved as only one optimization is needed in the new approach.
Conclusion: The plan-and-split approach produces same-quality plans meeting clinical objectives with only one optimization. It saves tremendous time in treatment planning for multi-fractionation radiotherapy.