SBRT Dosing for Central Lung Tumors

Definition and Dose Recommendations

Central tumors are defined as those located within 2 cm in all directions of any mediastinal critical structure, including the bronchial tree, esophagus, heart, brachial plexus, major vessels, spinal cord, phrenic nerve, and recurrent laryngeal nerve, and the recommended SBRT dose is 50 Gy in 5 fractions, as this provides optimal tumor control while minimizing toxicity to critical structures 1
It's essential to distinguish between "moderately central" tumors and "ultracentral" tumors (where the planning target volume overlaps the trachea or main bronchi), with SBRT not being appropriate for ultracentral tumors due to increased toxicity risk 1

Central tumor location carries a higher risk of treatment-related toxicity compared to peripheral tumors, with early studies using 60-66 Gy in 3 fractions for central tumors reporting serious and even lethal toxicity, and lower doses per fraction (such as 50 Gy in 5 fractions) demonstrating significantly lower toxicity rates 2

The optimal BED10 (biological equivalent dose with α/β = 10) for SBRT should be at least 100 Gy, with BED10 ranges of 83.2-106 Gy and 106-146 Gy showing the best outcomes 3

For tumors adjacent to critical structures, "risk-adapted" fractionation schemes should be employed, and for medically inoperable patients with tumors >5 cm and/or moderately central location, radical RT using more conventional or accelerated schedules is recommended over SBRT 1, 2

Advanced dose calculation algorithms (type B models) should be used for treatment planning, with planning target volume (PTV) accounting for respiratory motion, and planning organ at risk volume (PRV) margins used for critical serial organs in centrally located tumors 4