What are the indications and limitations of using Cone Beam Computed Tomography (CBCT) for lung imaging?

Indications and Limitations of Cone Beam Computed Tomography (CBCT) for Lung Imaging

CBCT is primarily indicated for image-guided radiotherapy in lung cancer and bronchoscopic diagnosis of peripheral pulmonary lesions, but has significant limitations including increased radiation exposure and should not be used routinely for short-term follow-up of lung conditions. 1, 2

Primary Indications for CBCT in Lung Imaging

Image-Guided Radiotherapy for Lung Cancer

• CBCT allows for more accurate patient setup in radiation therapy for lung cancer patients compared to traditional electronic portal imaging devices that only verify bony anatomy 1
• Both online and offline CBCT procedures are suitable for normal fractionation radiotherapy, with online verification being essential for stereotactic treatments 1
• Frequent CBCT imaging (more than once weekly) is particularly relevant when large anatomical changes are anticipated, such as in cases of atelectasis or bulky small cell lung cancer treated with concurrent chemoradiation 1
• CBCT enables verification of tumor position when motion management techniques like gating and active-breath hold techniques are applied 1

Bronchoscopic Diagnosis of Peripheral Pulmonary Lesions

• CBCT significantly improves navigation success for peripheral lung lesion biopsies, with navigation success rates of 76.3% when used as a primary approach 2
• When CBCT is combined with electromagnetic navigation bronchoscopy (EMN), navigation success rates increase to 87.5-89.9% per lesion 2
• CBCT-guided bronchoscopy with robotic assistance has been shown to reduce procedure times and radiation exposure compared to conventional flexible bronchoscopy with CBCT guidance 3

Clinical Benefits of CBCT in Lung Imaging

Radiotherapy Planning and Delivery

• Adaptive image-guided radiotherapy using CBCT can significantly decrease planning target volume (PTV) and dose to normal tissues, allowing for the possibility of dose escalation 4
• Online adaptive radiotherapy using CBCT can achieve relative decreases of 44% in PTV volumes, 31% in mean lung volume receiving ≥20Gy, and 31% in mean lung dose compared to 3D planning 4
• CBCT can be used to monitor tumor response during chemo-radiation therapy, with high correlation to diagnostic CT for tumor volume measurements (r=0.98) 5

Interventional Procedures

• CBCT with live 3D needle guidance allows faster lung radiofrequency ablation compared to conventional CT guidance, regardless of lesion size 6
• CBCT guidance may reduce the need for electrode repositioning during ablation procedures (27.8% with CBCT vs. 45.4% with CT) 6

Limitations and Considerations

Radiation Exposure

• CBCT increases radiation doses to patients, which should be taken into consideration in the final treatment plan 1
• Routine use of CBCT for short-term follow-up during pulmonary conditions is not recommended due to the risk of high cumulative radiation dose 1
• Clinicians should always consider the risk/benefit ratio related to annual radiation dose when prescribing CBCT scans 1

Technical Limitations

• While CBCT provides high navigation success for peripheral lung lesion biopsies, the overall diagnostic accuracy (72.4%) remains lower than the navigation success rate 2
• Image quality of CBCT may be inferior to conventional CT in certain applications, with a mean Dice's similarity coefficient of 0.66 (±0.16) when comparing tumor volumes 5

Patient-Specific Considerations

• Treatment delivery times can be prolonged with CBCT-guided stereotactic radiotherapy, which may necessitate repeated imaging to account for intrafractional tumor position changes 1
• For uncooperative patients, particularly in cystic fibrosis imaging, the risks related to sedation or anesthesia need to be considered when using advanced imaging techniques 1

Recommendations for Clinical Practice

• For lung cancer radiotherapy, CBCT should be used for patient setup verification, with online verification for stereotactic treatments and consideration of more frequent imaging when anatomical changes are anticipated 1
• For peripheral pulmonary lesion diagnosis, CBCT combined with electromagnetic navigation offers the highest navigation success and should be considered the preferred approach 2, 3
• A cautious approach is recommended for repeated CBCT imaging, with consideration of alternative imaging modalities such as MRI for conditions requiring serial imaging 1
• When using CBCT for interventional procedures like lung ablation, the faster procedure time should be balanced against the need for optimal diagnostic accuracy 6