Author: Xiangli Cui, Lingling Liu 👨🔬
Affiliation: Institute of Health and Medical Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Hefei Cancer Hospital, Chinese Academy of Sciences 🌍
Purpose:
Respiratory motion introduces substantial dose uncertainties in lung cancer radiotherapy, particularly affecting dose distribution in Simultaneous Integrated Boost-Stereotactic Body Radiotherapy (SIB-SBRT). This study investigates the impact of respiratory motion on dosimetric and biological outcomes in SIB-SBRT using a four-dimensional (4D) dose calculation approach.
Methods:
21 lung cancer patients treated with Volumetric Modulated Arc Therapy (VMAT) were included in this retrospective analysis. Four-dimensional CT (4D-CT) scans were utilized to create treatment plans based on the internal target volume (ITV) and planning target volume (PTV). 3D dose distributions were calculated on the average 4D-CT, and 4D dose distributions were derived by assigning 3D-plan monitor units (MUs) to corresponding respiratory phases. Accumulated 4D doses were generated through deformable image registration and compared to 3D doses. Dosimetric deviations in targets and organs at risk (OARs) were analyzed with key dosimetric parameters. Correlations between dose deviations and patient characteristics were explored.
Results:
Respiratory motion caused a reduction in V100 by 1.6% for ITV and 3.7% for PTV. TCP decreased by 0.1% for ITV and 4.0% for PTV. Gamma analysis revealed hot spots at the target periphery and cold spots within. Additionally, the biological dose analysis showed reduced tumor control probability (TCP) and improved normal tissue complication probability (NTCP) for the chest wall, while NTCP values for the lungs, heart, and spinal cord remained unchanged.
Conclusion:
Respiratory motion during SIB-SBRT significantly affects both dosimetric and biological outcomes, compromising target coverage and tumor control. The findings underscore the importance of personalized treatment planning, particularly for patients with significant respiratory motion or tumors near the diaphragm. The established thresholds for motion management provide practical guidance for improving treatment precision and minimizing normal tissue toxicity.