Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 13 3 2026 09 01 744 754 Tran Hung School of Engineering Physics, Hanoi University of Science and Technology, Hanoi, Viet Nam Nguyen Van Anh Department of Radiation Oncology and Radiosurgery, 108 Military Central Hospital, Hanoi, Viet Nam Le Duc Department of Radiation Oncology and Radiosurgery, 108 Military Central Hospital, Hanoi, Viet Nam Quach Mai Department of Radiation Oncology and Radiosurgery, 108 Military Central Hospital, Hanoi, Viet Nam Trinh Mai Department of Radiation Oncology and Radiosurgery, 108 Military Central Hospital, Hanoi, Viet Nam Tran Thoa Department of Radiation Oncology and Radiosurgery, 108 Military Central Hospital, Hanoi, Viet Nam Bui Bieu Department of Radiation Oncology and Radiosurgery, 108 Military Central Hospital, Hanoi, Viet Nam Hoang Thai Department of Radiotherapy and Medical Physics - Nghe An Oncology Hospital, Nghe An, Viet Nam Pham Lam 103 Military Hospital, Hanoi, Viet Nam Nguyen Thuong 175 Military Hospital, Ho Chi Minh, Viet Nam Quang Trung PHAM 108 Military Central Hospital 2024 12 02 2025 02 20 Purpose: This study aims to explore the effect of mean dose constraint in optimization shells on the reduction of normal lung dose in lung Stereotactic Body Radiation Therapy (SBRT) plans. Materials and Methods: This study investigated 28 VMAT-based lung SBRT plans optimized with three artificial shells, which were re-generated with the same setup and an additional mean dose constraint besides the maximum dose limit. Dosimetric measurements of target volume and Organs At Risk (OARs) were compared between the original plans and re-generated ones using the Wilcoxon signed-rank test at 5% level significance (two-tailed). Results: Replanning resulted in slight improvements in some parameters, such as R50% and the Gradient Measure (GM), which were reduced by 1.3% and 1.0%, respectively, with p < 0.05. However, there were slight increases in other parameters, such as D2cm and the maximum target dose, though these increases were not statistically significant. The Conformity Index (CI) remained nearly identical, with a mean value of 0.99 ± 0.03 for both original and re-optimized plans. Similarly, the V105% values were consistent, with mean values of 0.02 ± 0.13% in both groups. The parameters for dose deposited in normal lung tissue showed statistically significant reductions ranging from 1.0% to 1.7%. In addition, the mean dose to the spinal cord, esophagus, and skin was slightly reduced, but the mean dose to the heart showed a slight increase. Conclusion: The study found that adding mean dose constraints to optimization shells in lung SBRT plans can reduce normal lung dose while maintaining dose conformity to the target. However, there may be slight changes in some OARs such as the spinal cord, esophagus, and skin. These changes were not statistically significant. https://fbt.tums.ac.ir/index.php/fbt/article/view/1163 https://fbt.tums.ac.ir/index.php/fbt/article/download/1163/518