Lateral decubitus chest X-ray positioning (right side down)
An extra chest view, used when a routine one is not enough. The patient lies on their right side, the beam passes back to front (PA), straight on to the receptor with the tube horizontal, and the centring point is T7, mid-sagittal.
By the ScanFlo Editorial Team · Updated
In this section · X-ray positioning
- X-ray positioning guides
- Skull positioning
- Face & sinuses positioning
- Soft tissue neck positioning
- C-spine positioning
- Chest positioning
- Shoulder positioning
- Humerus positioning
- Elbow positioning
- Forearm positioning
- Wrist positioning
- Hand positioning
- T-spine positioning
- Abdomen positioning
- L-spine positioning
- Sacrum & SI joints positioning
- Pelvis positioning
- Hip positioning
- Femur positioning
- Knee positioning
- Tibia & fibula positioning
- Ankle positioning
- Foot positioning
Still being checked: a radiographer is reviewing this guide. If your department does it differently, follow your department.
Patient position
Right lateral decubitus. Lay the patient on the side where fluid is suspected, raised on two firm pads so the dependent chest wall is shown, arms above the head, back against the vertical detector.
Centring & collimation
Central ray
PACentre: T7, mid-sagittal.
Beam: PA, perpendicular to the receptor, horizontal beam.
Collimate: include the dependent chest wall fully
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 110 cm | Horizontal beam |
| Receptor | 24 × 30 cm | landscape |
| Placement | Erect (wall) bucky | Grid in |
| Angulation | None | Perpendicular to the receptor |
Marker & breathing
- Marker: marker on the up side, labelled decubitus
- Breathing: Breathe out and hold.
Exposure by patient size
Treat these as a starting point. Your detector, your generator and the patient in front of you will all move the numbers.
| Patient size | kV | mAs (chart) | mAs (DR default) |
|---|---|---|---|
| XS | 120 | 0.5 | 0.5 |
| S | 120 | 0.63 | 0.63 |
| M | 120 | 0.8 | 0.8 |
| L | 120 | 1.25 | 1.25 |
These start from a classic film-screen chart (120 kV, 2 mAs at 140 cm) and are adjusted for a digital detector at 110 cm. The DR column is what ScanFlo's console suggests; each step up or down changes the mAs by about a quarter.
Image quality checklist
- The dependent chest wall is not cut off.
- A free fluid level, if present, is horizontal.
- The anatomical side marker is visible, correct and clear of the anatomy.
- Collimation borders are visible on all sides, no wider than the area requested.
Faults & how to fix them
| Fault | Cause | Fix |
|---|---|---|
| Dependent side cut off | Patient lying on the table surface | Raise the patient on pads. |
Common questions
- Where do you centre for a chest lateral decubitus X-ray?
- The centring point is T7, mid-sagittal.
- What distance and beam angle does a chest lateral decubitus need?
- 110 cm from the tube to the receptor. The beam passes back to front (PA), straight on to the receptor with the tube horizontal.
- What size receptor, and do you need a grid?
- Use a 24 × 30 cm receptor, landscape, in the wall bucky. A grid is needed.
- What should the patient do with their breathing?
- Ask them to breathe out and hold it while you expose.
- What goes wrong most often on a chest lateral decubitus?
- Dependent side cut off. Usual cause: patient lying on the table surface. The fix: raise the patient on pads.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a chest lateral decubitus in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.