VMAT Grid Therapy: A Widely Applicable Planning Approach

Abstract

To describe a novel and practical volumetric modulated arc therapy (VMAT) planning approach for grid therapy. Methods and Materials: Dose is prescribed to 1.5-cm diameter spherical contours placed throughout the gross tumor volume (GTV). Placement of spheres is variable, but they must maintain at least a 3-cm (center to center) separation, and the edge of any sphere must be at least 1 cm from any organ at risk (OAR). Three concentric ring structures are used during optimization to confine the highest doses to the center of the spheres and maximize dose sparing between them. The end result is alternating regions of high and low dose throughout the GTV and minimal dose to OARs. High-intensity flattening filter-free (FFF) modes are used to efficiently deliver the plans, and entire treatments typically take only 15 to 20 minutes. Results: The approach is illustrated with 2 examples treated at our institution. Patient #1 had a 1703-cm 3 mediastinal mass and was prescribed 20 Gray (Gy) to 24 spherical regions within the GTV. Patient #2 had a 3680-cm 3 abdominal tumor and was prescribed 18 Gy to 32 spherical regions within the GTV. Both patients received additional consolidative radiation approximately 1 week after the initial VMAT grid treatment. Each patient experienced marked reduction in tumor size and symptomatic relief without treatment-related complications. Conclusions: We have described in detail a planning approach for VMAT grid therapy treatments that can typically be delivered in a clinically practical time span. The VMAT approach is especially useful for tumors that are surrounded by sensitive critical structures. As many centers offer VMAT treatments, the approach is widely accessible and can be readily implemented once appropriate patient selection and delivery processes are established.

Salvage therapy expands highly cytotoxic and metabolically fit resilient CD8 + T cells via ME1 up-regulation

“…1A) ( 17 ). In some patients, SFRT can produce a marked relief of severe symptoms, cause substantial tumor regression, and achieve above-average local disease control rates ( 18 ). While the biological mechanisms of the effectiveness of SFRT are still unknown, the heterogeneous dose distribution is hypothesized to be responsible for modifying tumor-reactive immune responses.…”

Resilient CD8+T cells maintain a high cytotoxic capacity by balancing ROS via ME1 upregulation

“…SFRT is unique in that it intentionally delivers a heterogeneous dose distribution providing alternating regions of very high and low doses throughout the tumor 15 . SFRT can produce dramatic relief of severe symptoms, cause significant tumor regression, and achieve above average local control rates 16 . The biologic mechanisms responsible for the effectiveness of SFRT are still unknown, but the heterogeneous dose distribution is hypothesized to be responsible for modifying tumor-reactive immune responses both locally and systemically.…”

Feasibility Study of 3D-VMAT-Based GRID Therapy

“…In addition, both shallow and deeply seated tumors were included, with distances from the proximal edge of the target to the skin surface ranging from 0 (skin surface) to 6.27 cm. Gram et al 12 showed a planning approach for using VMAT-GRID on 2 cases of large bulky tumors. The author's planning technique differs from ours because the GRID targets are placed manually, and the maximum doses are much higher than prescription (up to 56% higher).…”