Dosimetric impact of two multileaf collimator systems in simultaneous integrated boost volumetric modulated arc therapy for lymph node metastases in stage IIIC cervical cancer

Objective Patients with FIGO stage IIIC cervical cancer frequently present with complex lymph node metastases (LNM), and proximity to multiple organs at risk (OARs) poses challenges for volumetric modulated arc therapy with simultaneous integrated boost (SIB-VMAT) planning. This study compared orthogonal dual-layer and parallel dual-layer multileaf collimator (MLC) systems, assessing dosimetric performance to inform clinical practice in complex nodal boost scenarios. Methods This retrospective planning study included 45 patients with FIGO 2018 stage IIIC cervical cancer who underwent SIB-VMAT between February 2022 and March 2024. Patients were stratified according to LNM distribution into unilateral pelvic, bilateral pelvic, and para-aortic subgroups (n = 15 per subgroup). The planning target volume (PTV) received a prescribed dose of 45–50.4 Gy in 25–28 fractions, while metastatic lymph nodes (PGTVnd) received 54–63 Gy using the SIB technique. For each patient, SIB-VMAT plans were generated using an alpha orthogonal dual-layer MLC (α-MLC) system and a parallel dual-layer MLC (p-MLC) system under identical planning objectives and dose constraints. Dosimetric parameters of target volumes and OARs were analyzed to assess planning feasibility and system-dependent planning characteristics. Each system was evaluated within its clinically commissioned treatment planning environment to reflect real-world clinical practice. Results Clinically acceptable target coverage was achieved with both MLC systems across all LNM subgroups. Particularly in patients with bilateral pelvic LNM, the α-MLC system demonstrated slightly improved dose gradient control for the PTV, reflected by a lower gradient index (p 0.05). Other target-related dosimetric parameters for the PTV and PGTVnd, including D max , D 2 , D 98 , V 95 , V 110 , conformity index, and homogeneity index, were comparable between the two systems. Differences were observed in OAR sparing, with the α-MLC system consistently reducing doses to the small intestine, colon, rectum, bladder, femoral heads, cauda equina, and spinal cord across the overall cohort and within each LNM subgroup (p 0.05). Conclusion Both MLC systems achieved clinically acceptable target coverage across all LNM subgroups, while the α-MLC system demonstrated superior OAR sparing. These system-level differences may inform equipment selection and planning strategies in challenging nodal boost scenarios for advanced cervical cancer.