Setting a Base Frame: The First Step in the Linear Accelerator Installation Process

Installing a linear accelerator (Linac) starts with a crucial first step: setting the base frame. This foundational component ensures the stability and precision necessary for the Linac to function effectively, supporting its operation for decades.

Pre-Installation Requirements

Before a linear accelerator can be installed, all room renovations must be complete, adhering to the Original Equipment Manufacturers (OEM) specifications. This includes the electrical system to power the Linac, the cooling water system for the Linac itself, and the HVAC system to condition the air in the treatment room.

Base Frame Overview

For a Varian linear accelerator, the base frame is a large, rectangular steel frame connected to an additional circular steel frame that supports the turntable. Together, these pieces are embedded in the floor, providing a solid foundation. It supports the weight of the Linac, which can exceed 25,000 pounds (about 11,340 kg), depending on installed options. A pit must be formed in the floor to accommodate the base frame, electrical conduits, and water lines, ensuring precise dimensions for solid anchoring.

Installation Process

The process of setting the base frame involves careful placement and leveling. It must be perfectly level and embedded in concrete grout at the correct height to align with the floor. After positioning the base frame and pouring the concrete grout, it must cure for approximately two weeks to ensure it has sufficiently hardened before the Linac can be mechanically installed. This curing process is crucial for the stability and precision of the installation.

Ensuring Proper Alignment

Positioning the base frame accurately is vital to ensure that the Linac aligns with the room’s radiation shielding requirements. The location of the isocenter for a Varian machine is primarily determined by the base frame’s location, which must be precisely placed as specified by physics to prevent radiation from spilling outside the primary shielding. Due to the Linac’s weight and the need for substantial radiation shielding, these systems are typically installed on the ground floor or basement of a facility.

Types of Base Frames

Not all linear accelerators require base frames, but common models in the U.S., like the Varian Clinac Series and TrueBeam Series, do. When such a machine is installed, the base frame will either be:

• An existing base frame that previously supported an older model of linear accelerator. In many cases, a C-Series will be replaced by a new TrueBeam system, and the base frame may be interchangeable. This option is practical for upgrades within the same facility, minimizing the need for new construction.
• A brand-new base frame provided by the manufacturer. This is typical for new vaults or existing vaults that lack the proper base frame or have less precise base frames than current specifications require. New frames ensure that the most current technology and design standards are met, offering improved support and stability.
• A recycled base frame, especially when installing a pre-owned linear accelerator system. However, not all used base frames are suitable for reinstallation. Only those that have been carefully removed, remain undamaged, and thoroughly inspected, cleaned, and prepped for re-use are considered viable. This approach is often more cost-effective and environmentally friendly.

Conclusion

The base frame is essential for supporting and anchoring some Linac models. With proper installation, a base frame can serve multiple generations of machines over decades, underscoring its importance in the installation process.