The Relationship between the Number of Segments and Gantry Angle on the Complexity of Head and Neck IMRT Plans

Fatemeh Zahra  Nosrati; Mohsen  Bakhshandeh; Mahdi  Ghorbani; Ali Shabestani  Monfared; Soraya  Khafri

doi:10.18502/fbt.v13i1.20763

Fatemeh Zahra Nosrati Biomedical Engineering and Medical Physics, Department School of Medicine Shahid Beheshti University of Medical Sciences, Tehran, Iran
Mohsen Bakhshandeh Faculty of Allied Medical Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran
Mahdi Ghorbani Biomedical Engineering and Medical Physics, Department School of Medicine Shahid Beheshti University of Medical Sciences, Tehran, Iran
Ali Shabestani Monfared Cancer Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran
Soraya Khafri Social Determinants of Health Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran

DOI: https://doi.org/10.18502/fbt.v13i1.20763

Keywords: Radiotherapy; Intensity Modulated Radiation Therapy; Modulation Complexity Score; Number of Segments; Gantry Angle.

Abstract

Purpose: This study aims to investigate the relationship between the Modulation Complexity Score (MCS) and the number of Monitor Units (MUs), number of segments, and gantry angles.

Materials and Methods: Treatment planning was performed for 60 patients with head and neck tumors using the step-and-shoot IMRT technique on the RayStation Treatment Planning System (TPS). Treatment plans were divided into two groups, including 30 simple plans (group 1) and 30 complex plans (group 2). Then the relationship between the MCS and the number of Monitor Units (MUs), the number of segments, and the MCS per beam for different gantry angles in the two groups and all plans was investigated.

Results: The Pearson correlation results for both groups and all plans showed a strong relationship between the number of MUs and the MCS (p<0.001). This indication of the strong correlation between MCS and MU in head and neck treatment plans for the first group plans shows a better correlation with the MU. The Pearson correlation results for both groups showed a strong relationship between the number of segments and the MCS (p<0.001). The lowest MCS value or the highest complexity was related to the angles of 161-180 degrees, and the highest MCS value or the lowest level of complexity was for the gantry angles of 281-300 degrees.

Conclusion: The correlation between the number of MU, the number of segments, and the MCS in head and neck plans shows that these items can be used to control complexity and reduce dose uncertainties.