Comprehensive Evaluation of Rapidarc Dynamic for Cervical Cancer with Inguinal Nodal Involvement
Abstract
Purpose
Cervical cancer radiotherapy including inguinal lymph nodes involves large and complex targets prone to dose bridging between separated target components and increased dose to organs at risk (OARs), limiting dosimetric optimization. RapidArc Dynamic (RAD) is a VMAT optimization technique incorporating Static angle modulated ports (STAMPs) to improve dose control in such target and OAR geometries. This study evaluated the utility of RAD compared with a conventional RapidArc technique.
Methods
Twenty cervical cancer patients requiring inguinal nodal irradiation were replanned under identical prescription conditions (45 Gy in 25 fractions). RAD plans used two asymmetric arcs with the collimator fixed in static mode and eight static ports. A collimator angle of 90° was applied for inguinal nodal blocking, while 25–35° was used for cervix target coverage. STAMPs angles were selected based on beam’s-eye-view (BEV) and differed between arcs. A conventional 4-arc RapidArc plan and a faked-RAD (fRAD) plan—based on the RapidArc geometric framework with minimized STAMPs —were included for comparison. Evaluation metrics included PTV coverage, OAR doses, dose bridging suppression, monitor units (MU), optimization and calculation time, and blinded physician preference.
Results
RAD achieved PTV coverage comparable to RapidArc despite using half the number of arcs. With RAD, V45Gy of the bladder, rectum, and bowel was reduced by approximately 30–60%, and bone marrow V20Gy by 3–4%. PTV hotspots and dose bridging were suppressed. The fRAD approach showed limited improvement compared with RapidArc. Optimization and calculation time was reduced by approximately 37%, and RAD plans were preferred in blinded clinical review. MU remained clinically acceptable.
Conclusion
RAD provides equivalent target coverage with improved OAR sparing, reduced dose bridging, and enhanced optimization and calculation efficiency using a simplified two-arc geometry. fRAD offers a practical stepwise entry strategy, and RAD represents an effective solution for extended-field VMAT planning with complex targets.