Year: 2026 | Month: November | Volume: 13 | Issue: 11 | Pages: 143-153
DOI: https://doi.org/10.52403/ijrr.20261112
Impact of Segment Number on Plan Quality and Delivery Efficiency in IMRT Planning for Left-Sided Breast Cancer
Rahmat Putra Pamungkas1, Eko Hidayanto2, Catur Edi Widodo3, Susiyami Rahayuningsih4, Ridwan Eka Susanto5
1,2,3Department of Physics, Faculty of Science and Mathematics, Diponegoro University, Semarang, Indonesia
4,5Integrated Cancer Center, Nuclear Medicine and Molecular Theranostics Installation, Sardjito General Hospital, Yogyakarta, Indonesia
Corresponding Author: Rahmat Putra Pamungkas
ABSTRACT
Left-sided breast cancer presents a unique challenge in radiotherapy because of the close proximity of the target volume to critical organs, particularly the heart and ipsilateral lung. Intensity-modulated radiation therapy (IMRT) improves target dose conformity while reducing radiation exposure to surrounding normal tissues. However, treatment plan quality and delivery efficiency remain influenced by optimization parameters such as segment number. This study aimed to evaluate the effect of segment number on plan quality, organ at risk (OAR) dose, and delivery efficiency in IMRT planning for left-sided breast cancer. A retrospective dosimetric study was conducted using CT simulation data from 10 patients with left-sided breast cancer. Three IMRT plans with different segment numbers (20, 30, and 40 segments) were generated for each patient using the Monaco Treatment Planning System with a Monte Carlo dose calculation algorithm while maintaining identical planning conditions. Plan quality was evaluated using V95%, V100%, Conformity Index (CI), and Homogeneity Index (HI), whereas OAR evaluation included Heart Dmean, Left Lung V20Gy, and Right Lung V5Gy. Delivery efficiency was assessed using Monitor Units (MU) and delivery time. Statistical analyses were performed using repeated-measures ANOVA or the Friedman test, followed by appropriate post hoc analyses (p < 0.05). Increasing the segment number significantly improved plan quality, as demonstrated by higher V95%, V100%, and CI values together with lower HI values (all p < 0.05). Most improvements occurred when the segment number increased from 20 to 30, whereas increasing the number to 40 provided only limited additional dosimetric benefit. No significant differences were observed in Heart Dmean, Left Lung V20Gy, Right Lung V5Gy, or MU (all p > 0.05), whereas delivery time increased significantly with increasing segment number (p < 0.05). In conclusion, increasing the segment number improves target dose coverage, conformity, and homogeneity but has limited influence on OAR sparing. A 30 segment IMRT plan provides an optimal balance between plan quality and delivery efficiency for left-sided breast cancer, whereas increasing the number of segments to 40 mainly prolongs treatment delivery without providing substantial additional dosimetric benefit.
Keywords: Breast cancer, Segment number, Treatment planning, Plan quality, Delivery efficiency
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