RapidArc dynamic versus RapidArc: A multi anatomical-site dosimetric evaluation

RapidArc (RA) has advanced VMAT delivery; however, challenges remain in achieving optimal organ-at-risk (OAR) sparing in complex cases. RapidArc Dynamic (RAD), a next-generation Volumetric Modulation Arc Therapy (VMAT) technique, incorporates dynamic collimator rotation, embedded static fields, and a faster optimizer to enhance dose modulation. This study compares dosimetric outcomes between conventional RA and RAD across four anatomical sites.

A retrospective analysis was conducted on 40 patients (10 each for breast, lung SBRT, prostate, and head and neck cancers). Each case was initially treated with RA and subsequently replanned using RAD in Eclipse v18.1. Plans were evaluated using dose-volume histograms (DVH), and paired t-tests assessed differences in target coverage and OAR sparing (p < 0.05).

RAD maintained equivalent target coverage compared to RA across all sites. Significant OAR sparing was observed with RAD, including reduced mean heart and contralateral lung doses in breast cases, lower rectal and bladder doses in prostate cases, improved conformity and reduced spinal cord and lung doses in lung SBRT, and superior sparing of parotids, cochleae, and mucosal structures in head and neck cases.

RAD offers superior OAR sparing and improved dose conformity without compromising target coverage compared to conventional RA. These results support RAD's clinical adoption, particularly for anatomically complex or high-precision treatments. Further prospective studies are needed to assess the long-term clinical benefits.