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Category: Volume 10 Issue 11 November 2022
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Title: A Dosimetric Comparison of VMAT and IMRT Plan Quality for Nasopharyngeal Cancer Treatment using Varian Eclipse TPS

Authors: Lisha Warlaitthma, Shashi Sharma, Mithu Barthakur, Shachindra Goswami

 DOI: https://dx.doi.org/10.18535/jmscr/v10i11.10

Abstract

Aim: The aim of this study is to compare the dosimetric difference for radiotherapy of nasopharyngeal carcinoma (NPC) between volumetric-modulated arc therapy (VMAT) and dynamic intensity-modulated radiation therapy (IMRT) using Varian Eclipse TPS following simultaneously integrated boost (SIB) protocol.

Patients and Method: Fifteen patients with NPC underwent SIB protocol were retrospectively selected for this study. The Gross tumour volume (GTV) of NPC contained nasopharynx gross target volume and the positive neck lymph nodes, PTV1 contained the clinical target volume (CTV) of high-risk sites and the whole nasopharynx and PTV2 contained the CTV of low-risk sites. The prescription dose of PTV1 was 69.96 Gy/33 fractions, and for PTV2 59.4 Gy/33 fractions. VMAT (two full arcs) and IMRT (9 equally spaced fields) plans were designed for each patient using SIB strategies. The dose constraints were set for a high conformal and homogenous dose distribution to the PTV with minimal dose to the organ at risks (OAR).The plan was first done for IMRT, using the same dose constraints VMAT plans were generated. The monitor unit (MU) and other dosimetric difference between IMRT and VMAT were compared.

Results: The fraction of prescribed dose received by 95%of PTV volume showed a better result for IMRT, resulting in a significant difference with p < 0.05, while no significant differences were found for Homogeneity Index and Conformity Index (p > 0.05). Similarly for OARs and remaining volume at risk no significant differences were found between IMRT and VMAT. The total MU for IMRT (1837.67 ± 141.54) is more than VMAT (625.33 ± 49.02) with p <0.05.

Conclusion: This study shows that VMAT can achieve similar target coverage and homogeneity as IMRT except with fewer MUs and less delivery time compared to IMRT in cases of nasopharyngeal carcinomas.

Keywords: Nasopharynx, carcinoma, IMRT, VMAT, Monitor Unit, Dosimetry.

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Corresponding Author

Lisha Warlaitthma

Medical Physicist, Eden Medical Center, Dimapur, Nagaland 797112, India