Room: Track 6
Purpose: Treating multiple lung lesions synchronously using single-isocenter volumetric modulated arc (VMAT) stereotactic body radiation therapy (SBRT) plan improves treatment efficiency and patient compliance. Due to set up uncertainty, aligning multiple lung lesions on a single daily cone beam CT (CBCT) has shown dosimetrically unacceptable loss of target(s) coverage up to 60%. Herein, we propose RESIST for treating multiple lung lesions synchronously using a single-isocenter VMAT-SBRT plan mitigating setup uncertainties.
Methods: We identified thirteen patients with two lesions treated with a single-isocenter VMAT-SBRT plan using 6MV-FFF beam to 54 Gy in 3 fractions (n=3) or 50 Gy in 5 fractions (n=10) prescribed to 70-80% isodose line. To minimize setup uncertainties, each plan was re-optimized using RESIST with 6MV-FFF beam. RESIST utilizes a single-isocenter placed in the mediastinum. This allows a plan to be created for each tumor, while allowing both tumors to be treated sequentially during the same session. It uses a novel feature in Eclipse with dynamic conformal arc (DCA)-based dose and user-controlled field aperture shape before VMAT optimization. SBRT protocol criteria was used for plan evaluation.
Results: RESIST plans provided better target coverage and conformity, gradient indices, and lower dose 2 cm from target. RESIST plans demonstrated statistically significant lower doses to ribs, heart, bronchus, skin, esophagus, and normal lung V20Gy.
Conclusion: Using RESIST to treat synchronous lung lesions with VMAT-SBRT can significantly reduce normal tissue doses while reducing chance of a geometric miss due to setup uncertainties, allowing for matching each tumor sequentially. Placement of isocenter at patient’s mediastinum will avoid potential patient/gantry collisions, provide greater degrees of non-coplanar arcs, and eliminate the need for multiple couch movements during CBCT imaging. RESIST has been demonstrated for 2 tumors, but can be used for up to 5. Further validation and clinical implementation of this novel technique is ongoing.