Z. Wang; Department of Radiation Oncology, Xijing Hospital, Fourth Military Medical University, Xian, Shaanxi, China
Purpose/Objective(s): A new radiotherapy platform integrating a linear accelerator (linac) and gamma-knife has been approved for clinical use(NMPA: 20223050973; FDA: K210921), providing a novel radiation therapy technique combining X-rays and ?-rays. This study explores the dosimetric advantage of this technique for lattice radiotherapy (LRT) in patients with soft tissue sarcomas. Materials/
Methods: In this retrospective study, clinical linac treatment plans of 3 soft tissue sarcomas patients were selected to compare with combined plans using the new technology. The treatment consisted of two plans: the LRT plan with 15Gy/1F and the conventional plan with 50Gy/25F. The clinical linac treatment plans were generated using the technology company 13.5 treatment planning system(TPS) with VMAT technique based on technology company linac with 6MV, while the combined plans were generated using RT PRO TPS based on the new radiotherapy platform: A linac plan (6MV) was optimized to cover PTV and a focusing gamma plan was generated to cover the vertices. Dosimetric comparisons between the clinical treatment plans and combined plans were made to evaluate the ability of the technique to deliver high doses to the vertices while minimizing dose to non-LATTICE target volume within the GTV. Results: The LRT plans consisted of (14, 13, 15) high-dose vertices with a 1.5cm diameter and a 3cm separation placed within the GTV resulting in a total of (23.8cc, 22.1cc, 25.5cc) vertices volume for the three patients, respectively. Compared to the clinical treatment plans, the combined plans had higher D0.5cc(25.3 vs 18.3, 24.5 vs 18.7, 25.1vs 19.3)Gy, Dmean (18.9 vs 16.2, 19.2 vs 17.33, 18.5 vs 15.5)Gy, EQD2 (for D0.5cc, LRT plan)(74.4 vs 43.2, 70.4 vs 44.7, 73.4 vs 47.1)Gy and EQD2 (for D0.5cc, total plan)(124.6 vs 94.2, 121.4 vs 95.7, 124.5 vs 98.2)Gy to the vertices. Furthermore, the combined plans showed lower doses of GTV margin (3.4 vs 4.5, 4.4 vs 4.9, 4.1 vs4.8)Gy, and higher D10/D90 values of GTV (5.8 vs 3.5, 5.4 vs 3.9, 4.8 vs 2.8) demonstrating feasibility to reach very high dose fall-offs inside GTV. Conclusion: Based on the physical properties of X-rays and ?-rays, this new radiation therapy technique is a preferred treatment option for lattice radiotherapy of soft tissue sarcomas.
