Author: Pat Esposito, Ashley Klein, Carmine Verna, Ling Zhuang 👨🔬
Affiliation: Northwestern Medicine 🌍
Purpose: To evaluate dosimetric parameters and treatment delivery efficiency between volumetric modulated arc therapy (VMAT) and hybrid dynamic conformal arc (HDCA) on SRS and SBRT planning through statistical analysis.
Methods: A total of 10 patients with single tumor lesion treated in 2024 in our hospital were included in this study, including 7 multi-fraction SRS patients (3-5 fractions) and 3 SBRT patients (3-5 fractions) with average PTV volume of 33.3cc. Planning was done per Astro practice guideline for SRS and NRG BR-001 for SBRT. SRS plans were generated with 1mm dose grid size and SBRT plans were generated in 2mm dose grid size in Eclipse (Varian Inc., Palo Alto, CA) treatment planning system using non-co-planer beams. PTV conformity index (CI), Gradient index (GI), plan hotspot (D0.03cc) and Beam MUs were compared between VMAT and HDCA plans using paired t-test.
Results: For each patient, both VMAT and HDCA plans utilized the same optimization objectives and resulted in same PTV coverage for comparison purpose. The mean ± SD values of MUs for VMAT and HDCA were 606 ± 405 MUs and 444 ± 230 MUs retrospectively indicating MUs from HDCA were significantly less than MUs from VMAT (p= 0.001). The MU reduction leads to significant treatment time drop for treatment delivery. Hotspot (D0.03cc) produced by HDCA (119±7%) was slightly lower than that produced by VMAT (120±7%) with p= 0.3 due to less modulation. CI calculated from VMAT and HDCA were comparable (p=0.18). GI calculated from VMAT was statistically significantly smaller for VMAT than HDCA (p=0.003) while still clinically acceptable per protocols.
Conclusion: Eclipse HDCA planning offers comparable CI and acceptable GI for SRS and SBRT treatment while provides steep reduction of treatment delivery time.