Dosimetric Comparison of Three - Dimensional Conformal Radiation Therapy (3DCRT) and Posterior Partial Arc Volumetric Modulated Arc Therapy (VMAT) Plan for Craniospinal Irradiation

This study compares three dimensional conformal radiotherapy (3DCRT) and Posterior Partial Arc volumetric modulated arc therapy (VMAT) planning techniques for treating craniospinal irradiation.  Ten patients with Medulloblastoma were retrospectively considered for the study and replanned using 3DCRT and posterior partial arc VMAT techniques using MONACO 5.11, treatment-planning system (TPS). The dose prescribed for the planning target volume (PTV) was 36Gy in 20 Fractions, followed by a boost dose to the brain volume. The parameters such as Tumour coverage, the organ at risk (OAR) doses, conformity index (CI), homogeneity index (HI), and total monitor units (MU) were calculated for both plans. Comparison of the two planning techniques done using paired sample t-test.
PTV coverage in VMAT and 3DRT was 97.994±2.2533 and 94.041±2.24907, respectively. The mean CI in 3DCRT and VMAT was 1.3459±0.3279 and 1.1714±0.1238, respectively, and the mean HI in 3DCRT and VMAT was 1.1151±0.0247 and 1.0634±0.0198, respectively. OAR doses were comparable in 3DCRT and VMAT. The total MU in 3DCRT and VMAT were 198.12±8.9539 and 978.403±170.0104, respectively.
Posterior Partial Arc VMAT plans are superior to 3DCRT in target coverage, conformity index, and homogeneity index. The OAR doses in the two planning techniques were comparable whereas, the duration of treatment was higher in VMAT compared to the 3DCRT method. Additionally, low dose volumes are reduced in VMAT due to partial posterior arcs. Considering all the factors, it can be concluded from the study that Posterior Partial Arc VMAT plans are superior to 3DCRT.