Pragmatic Evaluation of Lung SBRT Dosimetry and Patient Collision When Using Couch Kicks
Abstract
Purpose
To evaluate the dosimetric plan quality metrics and possibility of gantry collisions when utilizing +/- 10° couch kicks in 3 arc VMAT lung SBRT plans. Although it has been shown that couch kicks provide better dosimetry for lung SBRT plans, it is still a question of if the added benefit outweighs the practical cost of time on the machine for LINAC simulation.
Methods
Clinical standard practice is to plan lung SBRT plans utilizing 3 VMAT arcs with couch positions at -10°, 0°, and +10° positions. Previously treated lung SBRT patients were simulated on the machine to evaluate arc rotation limitations and planned with arc limits accordingly. Previously treated lung SBRT patients are replanned with no couch kicks and full VMAT arcs, and then reoptimized to create a new plan similar to the original. Radformation’s CollisionCheck is used to assess any possible collisions with the table at 0° for all VMAT arcs. Plan quality metrics such as PTV D_max, D_mean, Conformity Index (CI), and Gradient Index (GI) are compared between the two plans. Additionally, relevant OAR DVHs are assessed such as lungs, esophagus, trachea, ribs, heart, and spinal cord.
Results
Most patients were able to have full VMAT arcs once all fields had their couch rotation set to 0°. Lung V20 showed consistently higher for the no couch kick plans but only at less than 1% difference. CI and GI were consistently worse for the no couch kick plans with an average detriment of 0.024 and 0.240 respectively. LINAC simulation is scheduled for 1 hour of time for all patients in ARIA.
Conclusion
Although couch kicks show consistently higher dosimetric and plan qualities, it is more time consuming for simulation and treatment. It is dependent on the clinic to determine if the benefits outweigh the cost.