Stereotactic Body Radiotherapy of a Lung Tumor With Large Respiratory Motion Using Real-Time Adaptive Motion Management: A Case Report.

Large respiratory motion presents a challenging issue for stereotactic body radiotherapy (SBRT) treatment of thoracic or abdominal lesions. In clinical practice, it is common to use the internal target volume (ITV) method to account for respiratory motion. This leads to a larger target volume than the real tumor volume. When the tumor motion is large, the ITV-to-tumor volumetric ratio increases significantly, causing a proportionally large amount of normal tissue to receive a high prescription dose. While there exist different approaches to reduce the ITV, adaptive motion management (AMM), e.g., the respiratory synchrony target tracking method used by CyberKnife (CK), presents an interesting one. In this report, we present a lung SBRT case in which the tumor exhibits huge respiratory motion. The elongated shape of the lesion and the motion made the treatment more challenging if a conventional ITV method was used. After being evaluated initially for the conventional ITV method, the patient was selected to be treated under adaptive motion management with CyberKnife. A dosimetric comparison was performed between plans with/without AMM. The results demonstrated the benefits of the application of AMM and may provide useful clinical data for the future practice of treating lesions with large respiratory motion.