Effectiveness of Varian Rapidarc Dynamic for Postoperative Radiotherapy for Cervical Cancer
Abstract
Purpose
Postoperative radiotherapy for cervical cancer involves large target volumes, making it challenging to achieve adequate dose homogeneity while sparing organs at risk (OARs). Multi-arc volumetric modulated arc therapy (VMAT) improves plan quality but often increases treatment delivery time. RapidArc Dynamic (RAD) is a novel technique that enables simultaneous optimization of static angle modulated ports (STAMPs) and dynamic collimator rotation. This study evaluated the clinical feasibility of RAD for postoperative radiotherapy in cervical cancer.
Methods
Treatment planning data from ten patients were transferred to a non-clinical Varian Eclipse system. Four treatment plans were generated and compared: a clinical two-arc VMAT plan reoptimized and calculated using Eclipse ver.18.1 (VMATrecalc); a RAD plan incorporating four STAMPs with manually defined collimator angles (RADSTAMP); a RAD plan using dynamic collimator optimization with minimal STAMP contribution (RADopt); and a fixed-collimator single-arc VMAT plan (VMATsingle). To eliminate the influence of beam data differences, VMATrecalc was used as the reference and was normalized such that D50% equaled the prescribed dose.
Results
RADSTAMP and RADopt achieved planning target volume (PTV) coverage (D95% and D98%) comparable to VMATrecalc, whereas VMATsingle showed inferior coverage. In terms of OAR sparing, RADSTAMP and RADopt reduced bowel bag V40Gy by approximately 2.2% and pelvic bone V10Gy by 7.5%–8.4% compared with VMATrecalc. Although the total number of monitor units increased substantially (by 76% for RADSTAMP and 64% for RADopt), consolidating delivery from two arcs to a single arc reduced overall beam delivery time by 19% and 35%, respectively.
Conclusion
RAD effectively mitigates the trade-off between plan quality and delivery efficiency. By integrating STAMPs with dynamic collimator rotation, RAD maintains target coverage comparable to multi-arc VMAT while reducing OAR doses and significantly shortening treatment times, demonstrating promising clinical utility.