Dosimetric Comparison of Rapidarc Dynamic and Rapidarc for Prostate Cancer: A Paired Planning Study
Abstract
Purpose
This study aimed to compare RapidArc Dynamic (RAD) and RapidArc (RA) for prostate cancer, focusing on organ-at-risk sparing, target dose conformity and homogeneity, and delivery efficiency. Both the averaged RAD performance and individual RAD configurations were evaluated.
Methods
Seven prostate cancer patients were replanned using five techniques: four RAD configurations—1 arc with 1 static angle modulated port (STAMP) (1arc1S), 1 arc with 3 STAMPs (1arc3S), 1 arc with 5 STAMPs (1arc5S), and 3 arcs with 1 STAMPs (3arc1S)—and 3 arcs RA plan. DVH parameters for the rectum, bladder, and bowel were analyzed. Target were assessed using conformity index (CI) and homogeneity index (HI) for PTV70 and CI for PTV50.4. Planning efficiency was evaluated by total monitor units and beam-on time. A two-step statistical approach was applied: comparison of averaged RAD versus RA using the Friedman test, followed by post-hoc pairwise comparisons between individual RAD configurations and RA.
Results
Compared with averaged RAD, RA demonstrated lower rectal high-dose exposure (Rectum V70Gy: p = 0.020) and reduced extreme bowel dose (Bowel D0.1cc: p = 0.018). In post-hoc analyses, individual RAD configurations showed differentiated performance. The 3arc1S configuration achieved superior target conformity for PTV70 (CI: p = 0.006) and improved dose homogeneity (HI: p = 0.021), with comparable rectal and bladder dose sparing relative to RA. RAD plans significantly reduced beam-on time compared with RA (p < 0.001), while differences in total MU were modest but statistically significant (p = 0.031). Boxplot analyses demonstrated consistent dosimetric trends across patients.
Conclusion
RAD provides dosimetric performance comparable to RA, while specific RAD configurations—particularly 3arc1S—offer improved target conformity, favorable dose homogeneity, and enhanced treatment efficiency. RAD represents a clinically feasible alternative planning strategy for prostate cancer radiotherapy.