Imaging doses from the Elekta Synergy X-ray cone beam CT system

Area of Science:

• Radiotherapy Physics
• Medical Imaging
• Radiation Dosimetry

Background:

• The Elekta Synergy machine uses kilovoltage (kV) X-ray imaging for cone beam CT (CBCT).
• Assessing the additional radiation dose from CBCT is crucial for patient safety.

Purpose of the Study:

• To quantify the additional imaging dose associated with CBCT on the Elekta Synergy.
• To compare these doses with established imaging modalities.

Main Methods:

• Cone beam CT dose index (CBDI) was measured in standard phantoms (head, lung, pelvis) at various kV and mAs settings.
• Weighted doses were compared with thermoluminescent dosimeter (TLD) measurements in a Rando phantom and on patient surfaces.
• The ImPACT CT Patient Dosimetry Calculator was used to estimate total effective dose.

Main Results:

• Measured in-air CBDIs varied by kV and mAs, with lower values at lower kV.
• Weighted CBDIs in phantoms ranged from 3.8 to 5.5 mGy/100mAs for body sites.
• Christie Hospital's CBCT protocols resulted in doses of 1.6 mGy (head), 6 mGy (lung), and 22 mGy (pelvis).

Conclusions:

• CBCT doses for head and lung scans are comparable or lower than electronic portal imaging (EPI) and CT.
• Pelvic CBCT doses are similar to EPI but higher than CT.
• Further development of low-dose CBCT techniques is recommended to minimize cumulative patient exposure, especially with repeated use for treatment verification.