Original Article

The relationship between the number of segments and gantry angle on the complexity of head and neck IMRT plans

Abstract

Purpose: The complexity of Intensity Modulated Radiation Therapy (IMRT) technique increases dose uncertainties. Therefore, limiting the complexity can be effective in reducing uncertainty. 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: 60 patients with head and neck tumors were selected. Treatment planning was performed using the step-and-shoot IMRT technique on the RayStation treatment planning system (TPS). Treatment plans were divided into two groups including 30 simple (group 1) and 30 complex (group 2) treatment plans. The MCS formula was coded and implemented in the RayStation TPS to calculate the MCS. The MCS of complex and simple plans were compared. 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). The R2 was equal to 0.67 for all plans, 0.77, and 0.71 for the first and second groups, respectively. 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 R2 value was 0.76 for the first group and 0.75 for the second group. 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. Conclusions: The results show correlation between the number of MU, the number of segments and the MCS in head and neck plans, so these items can be used to control complexity and reduce dose uncertainties.

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IssueVol 13 No 1 (2026) QRcode
SectionOriginal Article(s)
DOI https://doi.org/10.18502/fbt.v13i1.20763
Keywords
Radiotherapy Intensity Modulated Radiation Therapy Modulation Complexity Score number of segments gantry angle
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How to Cite
1.
Nosrati FZ, Bakhshandeh M, Ghorbani M, Shabestani Monfared A, Khafri S. The relationship between the number of segments and gantry angle on the complexity of head and neck IMRT plans. Frontiers Biomed Technol. 2026;13(1):67-76.