Room: Exhibit Hall | Forum 9
Purpose: To develop a robust, low-resource method to verify coplanar beam clearance and patient safety based solely on isocenter location and intended treatment technique for Varian TrueBeamÂ® and Elekta Agilityâ„¢ linear accelerators.
Methods: Physical measurements of distance from treatment head to isocenter and treatment table width for both machines were made. A plan is considered deliverable if the distance from the treatment isocenter to the most distal surface of the table, patient, or immobilization device in any Treatment Planning System (TPS) is less than the physical distance between treatment head and geometric isocenter (Scenario 1). If the tabletop is the clearance-limiting surface, its edges are cut off in the planning CT, and the isocenter is midline on the patient, the vertical distance from the treatment isocenter to the tabletop can be used instead (Scenario 2). Depending on the TPS measured value (Scenario 1/Scenario 2), the isocenter is either acceptable for treatment (<35cm/23cm), a clearance check is required (35-40cm/23-30cm), or a collision is imminent (>40cm/30cm) and the isocenter location or planning technique must be modified. For any extraneous conditions, a clearance check is required.
Results: The coplanar clearance verification tool was successful in retrospectively predicting collisions for five treatment plans, which would have eliminated re-planning and patient treatment delays. Additionally, this tool successfully validated the use of full VMAT arcs for a lung SBRT patient with a large body habitus and Alpha CradleÂ® immobilization. Dosimetry and physics staff have enthusiastically accepted and adapted this technique for clinical use.
Conclusion: A quick and simple coplanar clearance verification tool is presented. This robust tool prevents collision situations, therefore saving personnel time and enhancing efficiency for dosimetrists, physicists, and physicians. Decreasing re-planning, delayed treatment starts, and additional physics checks results in higher patient satisfaction and throughput, as well as decreased probability of errors.