Author: Christine V. Chung, Laurence Edward Court, Meena S. Khan, Ethan B. Ludmir, Rachael M. Martin Paulpeter, Saurabh Shashikumar Nair, Callistus M. Nguyen, Joshua S. Niedzielski, Luis Augusto Perles 👨🔬
Affiliation: MD Anderson Cancer Center, The University of Texas MD Anderson Cancer Center, UT MD Anderson Cancer Center, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center 🌍
Purpose: Spatially Fractionated Radiation Therapy (SFRT) has re-emerged as an efficacious treatment approach for bulky solid tumors. RapidArc Dynamic (RAD) has unique beam delivery capabilities that may be advantageous for Lattice Radiation Therapy (LRT), which is a widely adopted SFRT approach. Herein, we compared clinically acceptable LRT plans created using standard volumetric modulated arc therapy (VMAT) and RAD.
Methods: Ten bulky liver cancer patients receiving RT were retrospectively identified; VMAT-LRT and RAD-LRT plans were generated for all patients. Lattice spheres were placed in a standardized hexagonal pattern with alternating high-dose spheres (VTVH, vertex tumor volume high, analogous to peak dose) and low-dose control spheres (VTVL, vertex tumor volume low, analogous to the valley dose) spheres. Gross tumor volumes (GTVs)<1,000cm3 were planned with 1.0-cm diameters spheres, and GTVs>1,000cm3 used 1.5-cm diameter spheres (n=5), and a prescription of 20Gy to 80% of the high-dose target spheres (VTVH). LRT dose metrics were calculated (e.g., VTVH D80, VTVL Dmean) and compared using paired Wilcoxon sign-ranked test.
Results: For all 10 cases, RAD achieved better LRT plan quality, indicated by comparable prescription dose coverage (group mean, VTVH D80: 20.38 vs. 20.37Gy, VMAT-LRT vs. RAD-LRT), but significantly lower valley dose (group mean, VTVL mean dose: 3.57 vs. 2.40Gy, VMAT-LRT vs. RAD-LRT, p<0.001). Compared to VMAT-LRT, RAD-LRT proved more beneficial overall in LRT treatment planning efficiency: requiring fewer planning structures (8±1 for VMAT-LRT, 4±1 for RAD-LRT), planning time (22±9 mins for VMAT-LRT, 15±10 mins for RAD-LRT) and treatment fields (5±2 for VMAT-LRT, 1 for RAD-LRT). Peak-to-valley dose ratios were significantly higher for RAD-LRT (VTVH/VTVL D90 ratio: 7.26 vs. 15.28, p<0.001).
Conclusion: Compared to standard VMAT-LRT, LRT utilizing RAD showed superior plan quality and treatment planning efficiency. RAD offers a unique approach to this complex SFRT modality, allowing for quality plans without extensive planning time and expertise.