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Updated: Dec 2, 2025
Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
Published on: June 7, 2015
MLC tracking for lung SABR is feasible, efficient and delivers high-precision target dose and lower normal tissue
Jeremy Booth1, Vincent Caillet2, Adam Briggs3
1Northern Sydney Cancer Centre, Royal North Shore Hospital, Sydney, Australia; Institute of Medical Physics, School of Physics, University of Sydney, Australia.
Background And Purpose:
The purpose of this work is to present the clinical experience from the first-in-human trial of real-time tumor targeting via MLC tracking for stereotactic ablative body radiotherapy (SABR) of lung lesions.
Methods And Materials:
Seventeen patients with stage 1 non-small cell lung cancer (NSCLC) or lung metastases were included in a study of electromagnetic transponder-guided MLC tracking for SABR (NCT02514512). Patients had electromagnetic transponders inserted near the tumor. An MLC tracking SABR plan was generated with planning target volume (PTV) expanded 5 mm from the end-exhale gross tumor volume (GTV). A clinically approved comparator plan was generated with PTV expanded 5 mm from a 4DCT-derived internal target volume (ITV). Treatment was delivered using a standard linear accelerator to continuously adapt the MLC based on transponder motion. Treated volumes and reconstructed delivered dose were compared between MLC tracking and comparator ITV-based treatment.
Results:
All seventeen patients were successfully treated with MLC tracking (70 successful fractions). MLC tracking treatment delivery time averaged 8 minutes. The time from the start of CBCT to the end of treatment averaged 22 minutes. The MLC tracking PTV for 16/17 patients was smaller than the ITV-based PTV (range -1.6% to 44% reduction, or -0.6 to 18 cc). Reductions in mean lung dose (27 cGy) and V20Gy (50 cc) were statistically significant (p < 0.02). Reconstruction of treatment doses confirmed a statistically significant improvement in delivered GTV D98% (p < 0.05) from planned dose compared with the ITV-based plans.
Conclusion:
The first treatments with lung MLC tracking have been successfully performed in seventeen SABR patients. MLC tracking for lung SABR is feasible, efficient and delivers high-precision target dose and lower normal tissue dose.
Insights
Real-time tumor targeting using MLC tracking in lung SABR is feasible and efficient. This advanced technique allows for precise high-dose delivery to tumors while minimizing radiation to surrounding healthy lung tissue.
Area of Science:
- Radiation Oncology
- Medical Physics
- Oncology
Background:
- Stereotactic ablative body radiotherapy (SABR) for lung lesions requires precise tumor targeting.
- Real-time tumor motion tracking is crucial for accurate dose delivery in lung SABR.
- Current methods may involve larger planning target volumes (PTVs) to account for motion.
Purpose of the Study:
- To present clinical experience from the first-in-human trial of real-time tumor targeting using MLC tracking for lung SABR.
- To evaluate the feasibility, efficiency, and dosimetric outcomes of MLC tracking in lung SABR.
Main Methods:
- Seventeen patients with stage 1 non-small cell lung cancer (NSCLC) or lung metastases underwent electromagnetic transponder-guided MLC tracking for SABR.
- MLC tracking SABR plans used a 5 mm PTV expansion from the gross tumor volume (GTV).
- A comparator plan used a standard 4DCT-derived internal target volume (ITV) with a 5 mm PTV expansion; treatment delivery was continuously adapted based on transponder motion.
Main Results:
- MLC tracking was successfully implemented in all 17 patients (70 fractions), with an average treatment delivery time of 8 minutes.
- MLC tracking resulted in significantly smaller PTVs compared to ITV-based plans (up to 44% reduction).
- Statistically significant reductions in mean lung dose and V20Gy were observed, along with improved delivered GTV D98% accuracy.
Conclusions:
- The first clinical application of lung MLC tracking for SABR has been successfully demonstrated in 17 patients.
- MLC tracking is a feasible and efficient method for lung SABR, enabling high-precision target dose delivery.
- This technique leads to reduced radiation dose to normal lung tissue.
