Dosimetric Comparison of Three - Dimensional Conformal Radiation Therapy (۳DCRT) and Posterior Partial Arc Volumetric Modulated Arc Therapy (VMAT) Plan for Craniospinal Irradiation

Introduction: This study compares three dimensional conformal radiotherapy (۳DCRT) and Posterior Partial Arc volumetric modulated arc therapy (VMAT) planning techniques for treating craniospinal irradiation.  Material and Methods: Ten patients with Medulloblastoma were retrospectively considered for the study and replanned using ۳DCRT and posterior partial arc VMAT techniques using MONACO ۵.۱۱, treatment-planning system (TPS). The dose prescribed for the planning target volume (PTV) was ۳۶Gy in ۲۰ 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. Results: PTV coverage in VMAT and ۳DRT was ۹۷.۹۹۴±۲.۲۵۳۳ and ۹۴.۰۴۱±۲.۲۴۹۰۷, respectively. The mean CI in ۳DCRT and VMAT was ۱.۳۴۵۹±۰.۳۲۷۹ and ۱.۱۷۱۴±۰.۱۲۳۸, respectively, and the mean HI in ۳DCRT and VMAT was ۱.۱۱۵۱±۰.۰۲۴۷ and ۱.۰۶۳۴±۰.۰۱۹۸, respectively. OAR doses were comparable in ۳DCRT and VMAT. The total MU in ۳DCRT and VMAT were ۱۹۸.۱۲±۸.۹۵۳۹ and ۹۷۸.۴۰۳±۱۷۰.۰۱۰۴, respectively. Conclusion: Posterior Partial Arc VMAT plans are superior to ۳DCRT 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 ۳DCRT 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 ۳DCRT.

Keywords:

Medulloblastoma , Radiotherapy , ۳DCRT , VMAT