Clinical Implementation of Robust Multi-isocentric Volumetric Modulated Arc Radiotherapy for Craniospinal Irradiation

Abstract

Aims: To determine if multi-isocentric volumetric modulated arc radiotherapy for craniospinal irradiation (CSI-VMAT) can be implemented safely and accurately using robust optimisation in a commercially available treatment planning system. Our initial clinical experience is reported for the first 20 patients treated with the technique. Materials and methods: Patients received between 23.4 and 39.6 Gy (mode 23.4 Gy) in 13e22 fractions with CSI-VMAT. The heart mean dose was 4.2e10.3 Gy (median 5.3 Gy) for patients prescribed up to 24 Gy and 6.5e16.3 Gy (median 10.1 Gy) for patients receiving 35 Gy or more. The lung mean dose was 5.5e7.6 Gy (median 6.8 Gy) for patients prescribed up to 24 Gy and 6.9e11.1 Gy (median 10.0 Gy) for patients receiving 35 Gy or more. The robustness of the planning target volume D 0.1cm3 and D 99% to systematic errors in the isocentre superoinferior position of up to 5 mm was evaluated. These remained acceptable but were correlated to the length of the available beam overlap through the neck.Results: As of January 2021, one patient was deceased after 508 days and one patient was lost to follow-up after completing treatment. The median follow-up was 399 days (range 175e756 days) and progression-free survival was 131 days (34e490 days). Acute toxicities at Common Terminology Criteria for Adverse Events v5.0 grade 3þ included lowered white blood cell count (16/20), decreased platelet count (8/20), nausea (5/20), vomiting (2/20), pharyngeal mucositis (1/ 20) and oral mucositis (1/20). Three patients developed grade 4 neutropenia or decreased white blood cell count. Conclusions: CSI-VMAT can be implemented safely and accurately using robust optimisation functions in a commercially available treatment planning system.

Feasibility of using a dual isocentre technique for treating cervical cancer on the 1.5 T MR-Linac

“…Monaco is used for the treatment planning for the MRL as the Monte Carlo algorithm can account for the effect of the magnetic field. Eclipse (Varian Medical Systems, Palo Alto, USA) and RayStation (RaySearch, Stockholm) (Smyth et al 2022) have robust optimisation tools that can enable the creation of the junction regions between the two isocenters. This approach has recently been evaluated on the 0.35 T ViewRay system using an ArcCHECK phantom and film to show that these plans verified well (Placidi et al 2021).…”