| Schedule | Constraint | Source |
|---|---|---|
| 30–34 Gy / 1 fx Peripheral | Max dose <20.2 Gy | RTOG 0915 |
| D4 cc <10.5 Gy | RTOG 0915 | |
| 54 Gy / 3 fx Peripheral | D0.5 cc <30 Gy (optimal), <32 Gy (mandatory) | UK SABR Consortium 2019 |
| 50 Gy / 5 fx Central | Max dose 35–38 Gy | UK SABR consensus 2022 |
Quoted from eviQ 3389 and eviQ 4018, checked 2026-09-22. Full table with references →
The central airways: the trachea, the carina, the right and left main bronchi, the bronchus intermedius and the lobar bronchi. The exact extent of the “proximal bronchial tree” is defined by each protocol.
The trachea and bronchi carry air between the throat and the lungs.
The PBT is the structure most associated with the idea of a central lung tumor. Tumors close to the central airways were linked to serious toxicity in early SBRT experience, which is why many protocols treat central and peripheral tumors differently and why RTOG 0813 was designed specifically for central tumors. Endpoints listed in the Timmerman 2022 tables include impaired clearing of airway secretions (“pulmonary toilet”) and stenosis with collapse of the lung beyond it (atelectasis).
Note that sources split the airways differently. Timmerman 2022 lists “Trachea and large bronchus” and “Bronchus, smaller airways” as separate rows (the smaller-airways row appears in the 1–8 fraction tables), and footnotes the trachea and large bronchus to avoid circumferential irradiation.
Kong 2011 contours the proximal bronchial tree as one structure on a mediastinal window, including the airway wall (mucosa, submucosa and cartilage rings) and the air channel:
For lung SBRT, Kong describes the central zone as a 2 cm expansion of the proximal bronchial tree in every direction except upward.
Timmerman 2022 (Tables 8–11, written for its SBRT dose tables) uses a longer "trachea and large bronchus" structure: the trachea and cartilage rings from 10 cm above the PTV, down into the bronchi, ending at the first branching of the named lobar bronchus.
A thoracic organ-at-risk contouring atlas with discussion of dose limits, covering the lung, proximal bronchial tree, esophagus, spinal cord, ribs and brachial plexus. A published letter in response discusses esophageal delineation.
An editorial history of the UT Southwestern SABR constraint tables — often called the “Timmerman tables” — covering how they were developed and revised, and their relationship to AAPM TG-101 and NRG/RTOG protocols. Tables 2–11 separate serial tissues (listed with a volume, a volume max and a max point dose) from parallel tissues (listed with a critical volume and a critical-volume dose max). In Tables 2–7 a footnote defines “point” as ≤0.035 cm³; Tables 8–11 add a contouring-instructions column for each structure.