2898 - Clinical Efficacy and Dosimetric Comparison of Hybrid Lattice Radiotherapy Using CyberKnife and Conventional Linac for Bulky Tumors
Presenter(s)
Q. Han1, W. Liu2, and S. Tian1,3; 1Department of Radiation Oncology, Peking University Third Hospital, Beijing, China, 2peking univerisiyt third hospital, beijing, China, 3Peking University 3rd Hospital, beijing, China
Purpose/Objective(s):
Bulky tumors remain a major challenge in radiation oncology due to their severely hypoxic intratumoral microenvironment and mass effect on adjacent organs at risk (OARs). Lattice Radiotherapy (LRT), a three-dimensional spatially fractionated technique, addresses these challenges by creating high-dose vertices and low-dose valleys to potentiate tumor control through modulation of hypoxia and induction of bystander effects. This study aimed to evaluate the clinical safety and efficacy of a hybrid LRT approach combining a conventional linear accelerator (Linac) with the CyberKnife system and to compare the dosimetric characteristics of the two modalities in generating Lattice dose distributions.
Materials/Methods:
A retrospective analysis was performed on 17 patients with bulky solid tumors treated at our institution. All patients received a hybrid radiotherapy regimen comprising conventional fractionated radiotherapy delivered by a standard Linac to cover the entire tumor volume, supplemented by a high-dose Lattice boost delivered to predefined intratumoral vertices using the CyberKnife system. The single-fraction dose to each vertex was 15 Gy. For dosimetric comparison, both CyberKnife-based and Linac-based (VMAT/IMRT) Lattice plans were generated for each patient. Key endpoints included short-term clinical efficacy, toxicity profiles, Peak-to-Valley Dose Ratio (PVDR), and treatment delivery time.
Results:
All patients completed the planned treatment without interruption. With a median follow-up of 15 months, the overall objective response rate (ORR) was 93%, with a mean tumor volume reduction of 81%, accompanied by marked improvement in tumor-related symptoms. The hybrid regimen was well-tolerated, and no acute toxicities of Grade 4or higher were observed. Dosimetric analysis demonstrated that CyberKnife-based Lattice plans achieved a significantly higher mean PVDR at the vertices (5.8) compared with Linac-based plans (3.2) (P < 0.01), indicating steeper dose fall-off and more pronounced dose heterogeneity within the target. In contrast, the conventional Linac exhibited superior time efficiency, reducing the average treatment delivery time per fraction by approximately 40minutes compared with CyberKnife.
Conclusion:
Hybrid Lattice Radiotherapy combining CyberKnife with a conventional Linac is a safe and feasible strategy for the management of bulky tumors and yields encouraging short-term clinical outcomes. Dosimetric data confirm that CyberKnife provides a distinct advantage in generating high-quality Lattice dose distributions with higher PVDR, which may be critical for leveraging the biological effects of LRT, including modulation of hypoxia and potential immune-mediated responses. Meanwhile, the conventional Linac offers substantial gains in treatment efficiency.