RapidArc dynamic versus IMRT and VMAT for endometrial cancer SIB radiotherapy

Abstract

Radiotherapy with simultaneous integrated boost (SIB) for endometrial cancer requires highly conformal dose distributions to reduce toxicity. RapidArc Dynamic (RAD), a novel technique combining dynamic arc delivery with strategic gantry pauses, may improve organ-at-risk (OAR) sparing. This study aimed to compare RAD with conventional IMRT and VMAT for endometrial SIB radiotherapy, specifically evaluating the OAR sparing capabilities of the RAD technique in endometrial cancer treatment. Thirty patients with high-intermediate risk endometrial cancer were retrospectively enrolled. Three plans (RAD, IMRT, VMAT) were generated per patient, prescribing 50.4 Gy to the planning target volume (PTV) and 61.6 Gy to the nodal clinical target volume (CTVn) in 28 fractions. Plans were evaluated for OAR dose constraints, conformity index (CI), 50% dose spillage ratio ( $$\:{R}_{50}$$ ), monitor units (MU), and modulation complexity score (MCS). RAD plans demonstrated superior OAR sparing, with fewer and less severe constraint violations for the bladder, rectum, small intestine, and bone marrow compared to IMRT and VMAT (Mann-Whitney U test, P  < 0.05). RAD achieved a significantly higher average CI (0.833) than two-arc VMAT (0.813) and demonstrated the lowest average $$\:{R}_{50}$$ (3.45) compared to both IMRT (3.86) and VMAT (3.67). Furthermore, while VMAT required the fewest MU (527.8), RAD (1314.7) used significantly fewer MU than IMRT (3334.0) and exhibited higher MCS, indicating less complex delivery than IMRT. RAD provides superior OAR protection and steeper dose fall-offs compared to VMAT, while maintaining high target dose conformity and potentially improving delivery efficiency. It represents a promising technique for endometrial SIB radiotherapy, combining the advantages of IMRT and VMAT. Not applicable.