Feasibility of lattice radiation therapy using a noncoplanar vertex arrangement and dynamic conformal arcs

Current Lattice radiation therapy (LRT) mainly uses inverse IMRT/VMAT optimization, which is time-consuming and complex; however the high modulation complexity compromises dosimetric accuracy and blurs the peak‑to‑valley dose ratio.

This study presents a simple noncoplanar vertex arrangement for dynamic conformal arc (DCA)‑based LRT and evaluates its feasibility.

Different noncoplanar vertex geometries were generated in a water phantom, and DCA‑based LRT plans were designed using Eclipse v15.6 (Varian). The LRT target volume (LTV) was the union of all vertices. Single‑fraction 20‑Gy plans were generated with three coplanar 6‑MV FFF beams and calculated with AcurosXB calculation. Optimal vertex geometry was selected based on high‑dose proportion (measured with the volume ratio of prescribed dose structure to GTV [V_Dp / V_GTV], and the volume ratio of LTV to GTV [V_LTV / V_GTV]), GTV dose metrics, heterogeneity(measured with peak-to-valley-dose-ratio [PVDR], Volume Dose Ratio [VDR] and other three dose ratios defined as Dose matrix of 'peak' / 'valley' [Dp / D_{95% Gap}, D_{mean LTV} / D_{mean Gap}, and D_{2cc GTV}/ D_{95% Gap}]), valley dose (D_{95% Gap} and D_{5% Gap}) and normal tissue(NT) max dose, dose profiles/isodose distributions and plan complexity (MCS, SAS, MU/cGy). The same strategy was applied to two gastrointestinal stromal tumor (GIST) patients with evaluation of OAR sparing and planning time.

In the phantom, six noncoplanar vertex configurations and one coplanar vertex configuration were generated, and corresponding DCA plans were designed for each. All plans achieved a high‑dose volume proportion exceeding 1% and EUD_GTV of 5.07 Gy - 6.78 Gy, with high dose heterogeneity (high PVDR, Dp / D_{95% Gap}, D_{mean V} / D_{mean Gap} and moderate VDR). Plan complexity remained low across all configurations, with MCS ranged 0.68-0.79. Optimal vertex geometry was 1-cm diameter with a 4-cm center‑to‑center distance, providing a favorable balance between dose heterogeneity and valley dose sparing. Moreover, the DCA plan based on noncoplanar vertex arrangement yielded dose distributions comparable to those of the non-coplanar plan with couch rotation. Importantly, both normal tissue (NT) doses in all phantom plans were very low. The clinical applicability was verified in two patients, with all dosimetric parameters meeting the recommended LRT ranges. Consistent with the phantom findings, patient NT and OAR doses remained far below the SBRT constraints, with a total planning time of ∼1 hour per patient, supporting the safety and translational potential of this approach.

DCA‑based LRT with noncoplanar vertices is feasible on linacs, simplifying planning and enabling accurate delivery. It offers a valuable alternative method for patients with couch rotation limit. Optimal vertex arrangement with 1‑cm diameter and 3.5-4 cm center to center distance obtained in water phantom. Two patient cases met LRT criteria, with a total planning time of approximately one hour per patient, supporting clinical applicability in complex anatomies.