SU‐E‐T‐321: Dosimetric Evaluation of Non‐Coplanar Arcs in VMAT Planning for SBRT Lung Cases: A Planning Study

TL;DRAbstract

Purpose: Investigate use of standardized non‐coplanar arcs to improve plan quality in lung Stereotactic Body Radiation Therapy(SBRT) VMAT planning. Methods: VMAT planning was performed for 9 patients previously treated with SBRT for peripheral lung tumors (tumor size:12.7cc to 32.5cc). For each patient, 7 VMAT plans (couch rotation values:0,5,10,15,20,25,and 30 deg) were generated; the coplanar plans were pushed to meet the RTOG0915 constraints and each non‐coplanar plans utilized the same optimization constraints. The following plan dose metrics were used (taken from RTOG 0915): D‐2cm: the maximum dose at 2 cm from the PTV, conformality index (CI), gradient index (GI), lung volume receiving 5 Gy (V5) and lung volume receiving 20 Gy (V20). The couch collision clearance was checked for each plan through a dry run using the couch position from the patient's treatment. Results: Of the 9 cases, one coplanar plan failed to meet two protocol guidelines (both gradient index and D‐2cm paramete

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