Practical Implementation of VMAT Based Craniospinal Irradiation (CSI) for Metastatic Leptomeningeal Disease
Abstract
Purpose
VMAT based cerebrospinal irradiation (CSI) using photons has emerged as a palliative treatment approach for patients suffering from metastatic leptomeningeal disease. In this work we describe the experience introducing VMAT CSI into clinical use.
Methods
Patients were immobilized using the Orfit all-in-one board and open-face head/neck/shoulders and chest/abdomen thermoplastic masks for CT-simulation. Treatment planning was automated using a custom ESAPI script in Varian Eclipse V18. The script sets up the isocenters/fields, creates necessary optimization structures, and generates optimization goals. All plans use 6 MV photon energy and three isocenters with 7 full arcs (3-2-2 configuration). Treatment delivery includes CBCT imaging at each isocenter. In-house software was implemented to ensure alignment imaging residuals remained under PTV expansion margins. In-vivo dosimetry was performed using EPID based transit dosimetry for each fraction.
Results
Twenty patients completed treatment to either 3000cGy in 10fx, 3000cGy in 15fx or 2400cGy in 12 fs. PTV V100%=95% was achieved for all cases. All dose objectives from Yang et al. JCO 2022. Table 1A, were achieved except for individual Lung V5Gy90% at 5%/5mm for each individual field.
Conclusion
VMAT based CSI using photons for the management of leptomeningeal disease can achieve organ sparing comparable to that reported in proton studies except for low exit dose anteriorly. Dose feathering among fields allows for treating with only one plan without the need to shift junctions improving safety and reducing the likelihood of hotspots or gaps in treatment.