Volumetric Modulated Arc Therapy (VMAT) Craniospinal Irradiation (CSI) for Children and Adults: A Practical Guide for Implementation

Purpose: Volumetric modulated arc therapy (VMAT) craniospinal irradiation (CSI) has been shown to have significant dosimetric advantages compared to 3-dimensional conformal therapy but is a technically complex process. We sought to develop a guide for all aspects of the VMAT CSI process and report patient dosimetry results.

Methods And Materials: We initiated VMAT CSI in 2017 and have regularly revised our standard operating procedure for this process since then. Herein, we report a detailed template for the entire VMAT CSI process from initial patient setup and immobilization at time of computed tomography (CT) simulation to contouring and treatment planning, quality assurance, and therapy delivery. The records of 12 patients who were treated with VMAT CSI were also retrospectively reviewed.

Results: Patient age ranged from 2 to 59 years with 5 pediatric patients (age <18 years), 5 young adults (age 18-35 years), and 2 older adults (age >35 years). The majority of patients (67%) had medulloblastoma. CSI dose ranged from 21.6 to 36 Gy, with a median of 36 Gy. The median CSI planning target volume was 2383 cc with a median V of 99.8% and median 0.03 cc hotspot of 112.5%. The average V was 7.4% and the average conformality index was 1.01.

Conclusions: VMAT CSI has potentially significant dosimetric and acute toxicity advantages compared to 3-dimensional conformal. However, proper procedures need to be in place throughout the process in order to be able to realize these potential advantages. We herein describe our detailed standard operating procedure for VMAT CSI. Recognizing the scarcity of proton beam centers in many areas, VMAT CSI represents a feasible treatment with more widespread availability.