Seismic reinforcement of a linac installation

Abstract The local building requirements to secure medical equipment in seismically active areas in the United States are based on recommendations of the American Society of Civil Engineers. In our institution we have recently acquired new linear accelerators, one of which had to be installed in an existing vault and one in a new vault. Since we are in a seismic active area, changes in the local code required us to start placing the new linacs seismically stable. Here, we describe the necessary steps taken to ensure a seismically sound installation of our linacs. For the linac installation to be seismically stable, the linac base frame has to be seismically fixed into the vault floor. The installation of a new linac into an existing vault requires verification of a structurally sound base frame. Knowledge of the previously applied fixation of such is needed and exploratory removal of grouted floor helped in the verification. Understanding the additional load requirements for the locality allows to account for the existing fixation and can potentially reduce the work needed to achieve seismic fixation requirements. For a prospective seismic installation the new linac base frame can be directly installed with the necessary strength. In addition the actual workflow is straight forward and vendor recommendations can be used. In both cases the vendor provided seismic calculations serve as baseline from which a facility should be work from. It is the facilities task to verify the correct installation of a linac in their specific location. An understanding of the seismic landscape can facilitate an appropriate installation at minimal additional cost.

Since we are in a seismic active area, changes in the local code required us to start placing the new linacs seismically stable. Here, we describe the necessary steps taken to ensure a seismically sound installation of our linacs. For the linac installation to be seismically stable, the linac base frame has to be seismically fixed into the vault floor. The installation of a new linac into an existing vault requires verification of a structurally sound base frame. Knowledge of the previously applied fixation of such is needed and exploratory removal of grouted floor helped in the verification.
Understanding the additional load requirements for the locality allows to account for the existing fixation and can potentially reduce the work needed to achieve seismic fixation requirements. For a prospective seismic installation the new linac base frame can be directly installed with the necessary strength. In addition the actual workflow is straight forward and vendor recommendations can be used. In both cases the vendor provided seismic calculations serve as baseline from which a facility should be work from. It is the facilities task to verify the correct installation of a linac in their specific location. An understanding of the seismic landscape can facilitate an appropriate installation at minimal additional cost.  Figure 1 shows a map of the surface faults of the ISB along the Wasatch Front of Utah. which were signed into law by the Utah state legislature, were consulted during the planning phase. It was noted at this point that the current implementation of seismic fixations (i.e., the existing base frame) no longer met the updated state building code requirements.
Since both projects were considered new implementations, the updated state requirements were required to be adhered to for both projects.
We believe that it may be unappreciated that many radiation therapy facilities are located in seismically active areas within the US and are therefore required to adhere to updated building codes. This work details the steps taken by our institution to address the seismic requirements for an existing vault (anchoring for an existing baseframe) and also for implementing seismic anchoring in a new vault. | 167 (VUB); however, the basic principles of seismic fixation can be applied to any linac frame. We are hopeful that by presenting this work we can assist other departments in seismically active areas at being proactive in considering and possibly planning for seismic requirements in their next linac purchase, with the hope that delays and inefficiencies might be avoided, and safety might be improved.

| DESCRIPTION
A licensed structural engineer was engaged in both cases to evaluate/design the anchoring of the equipment to the building structure based on anticipated local earthquake forces and the local code requirements for the anchors themselves.

2.A | Varian Universal Baseframe (VUB)
A linac installation (VUB, linac, and couch) will place more than To minimize disruption and potential distortion/level to the existing VUB, one of the known fixation bolt locations closest to the strongest area of the baseframe (see Fig. 2) was chosen to visually confirm bolt type and weld-pad availability. We measured levelness and concentricity of the VUB before the start of the project and after the testing/installation phase for consistency.
Initially a 4" core-drill and later a hand chisel were used to remove the flooring as needed to avoid damage to the existing baseframe. The first excavation established existing welding pad and dimensions. The fixation bolt type was the standard Bossard anchors. Figure 3  For the modification, we enlarged the existing test hole and added three similar sized holes in close proximity to where the baseframe weldpads were expected. Figure 4 shows an example F I G . 3. On the left is a cross section of the test hole created to evaluate the existing frame and anchors used. Next to it is a photo of the cleared frame, with a welding-pad and bolt outlined in red. With enough room for welding and drilling work, the locally specified 90°angle braces were spot welded on. After spot welding, the Hilti anchors were placed as per installation requirements but not torqued to specification yet. In a final step, the L brackets were fully welded and bolts torqued to specification under the direct supervision of a state inspector who then approved the installation. In order to avoid the frame being pulled by the welding (e.g., by heat deformation or structural deformation) all brackets were welded in a specific weld sequence, resulting in a three-sided welded connection between the L bracket and the welding pad of the frame.
Lastly, the welds and the bolt-torque were inspected by a code F I G . 5. The inspected weld and bolted seismic fixation for the existing base-frame.
showing the final bolt pattern as installed to the existing VUB to achieve seismic code requirements. The required smaller angle irons and special anchors were sourced locally and installed under the observation of an official code inspector.
inspector before the VUB was grouted in with above 3000 psi strength concrete.

| DISCUSSION
Any earthquake of a substantial magnitude is likely to cause a radiation therapy department to stop treatments until all devices have been verified for function and accuracy. The purpose of additional seismic anchoring for a VUB is intended to prevent staff and patients in the room from being injured by dislodged and falling machinery during the actual quake.
It is up to each facility to understand and interpret the predictions of seismic maps for their specific location. Given that almost 50% of the continental US is considered 'seismically active', we believe that centers are well advised to carefully consider whether seismic anchoring is required/advised for your particular region. For prospective seismic anchoring, the material cost are generally less than $1,000 and labor amounted to roughly two man-days, including inspection. The more involved retrofitting installation of seismic anchoring, which was deemed to be required for our site, introduced approximately $50,000 in additional cost. This total included engineering, special inspections, demolition, concrete cutting, welding, torqueing of bolts, patching the concrete, and repairing the floor.
While it is clearly preferable from a cost and efficiency perspective to perform seismic anchoring prospectively, when necessary, retrofitting seismic bracing can be effectively accomplished.

| CONCLUSION
Seismic activity for each institution's region should be carefully con- MS drafted an outline and did write the manuscript in consultation with VS, AP and PR. All authors provided critical feedback and helped shape the structure of the manuscript as well as the proof reading and formulation.

CONFLI CTS OF INTEREST
The authors report no conflict of interest for this publication.