SU-E-T-139: Dynamic Conformal Arcs Vs. VMAT for Stereotactic Lung Target Treatment Planning

Abstract

Purpose: To investigate if Dynamic Conformal Arcs (DCA) can be used to achieve similar target coverage and conformality as that of using VMAT for Stereotactic Body Radiation Therapy (SBRT) for Lung cases. Methods: We retrospectively re-planned 11 patients that were treated with SBRT for lung tumors using only a single conformal arc, broken into three or four arc segments and weighted differentially in order to achieve the dosimetric constraints as outlined in RTOG 0915 protocol. These re-plans of using DCA were compared with those of using VMAT in terms of the Planning Tumor Volume (PTV) coverage goals, Maximum Dose 2 cm away (D 2cm), High Dose Spillage, Intermediate Dose Spillage, Lung volume getting 5 Gy (V5), and number of monitor units (MU). Results: Of the 11 cases, only three DCA plans failed the D2cm parameter, and one VMAT plan failed. None of the 11 patients failed the High Dose Spillage in either technique. For Intermediate Dose Spillage, one DCA plan failed and none failed for VMAT plans. The average V5 for DCA was 10.5 percent, with VMAT reporting 11.7 percent. The average number of MU for DCA and VMAT were 2605 and 3451, respectively. Conclusion: DCA is able to achieve very similar treatment planning goals as that of using VMAT in treating SBRT Lung tumors in most cases with simplicity. In addition, the DCA technique produces an acceptable plan with lower V5 in less MU when dose to OAR concerns are at minimum. However, DCA has shown its limitations when the target is close to multiple OAR.