Evaluation of Radiation Dose to Thoracic Organs from 3D Versus 4D CBCT Using Radiophotoluminescent Glass Dosimeters
Abstract
Purpose
Four-dimensional cone-beam computed tomography (4D-CBCT) provides respiratory motion–resolved imaging for image-guided radiotherapy (IGRT) in thoracic treatments but may increase imaging dose compared with conventional three-dimensional CBCT (3D-CBCT). This study compares thoracic organ doses from 3D- and 4D-CBCT using radiophotoluminescent glass dosimeters (RPLGDs).
Methods
Imaging dose measurements were performed using an Alderson Rando anthropomorphic phantom instrumented with RPLGDs model GD-352M calibrated at 70 kVp (HVL: 2.9 mm Al). Dosimeters were placed in thoracic organs, including the lungs, heart, esophagus, thyroid, thymus, breast, and skin. Standard clinical 3D-CBCT (125 kV, 270 mAs) and 4D-CBCT (125 kV, 671 mAs) protocols were delivered using a Varian TrueBeam linear accelerator. Organ doses were measured and compared between imaging protocols.
Results
For 3D-CBCT, organ doses of 5.1 ± 1.4, 5.8 ± 0.6, 6.2 ± 0.2, 5.8 ± 0.6, 4.3 ± 0.3, 2.5 ± 0.2, and 2.4 ± 0.1 mGy were measured for the heart, skin, thymus, lungs, breast, esophagus, and thyroid, respectively. Corresponding 4D-CBCT doses were 15.0 ± 0.5, 12.9 ± 14, 12.3 ± 0.4, 10.6 ± 4.2, 8.0 ± 1.0, 1.8 ± 0.0, and 1.8 ± 0.1 mGy. Overall, 4D-CBCT resulted in higher organ doses, primarily due to longer acquisition time, increased mAs and projection numbers. In contrast, the esophagus and thyroid received lower doses during 4D-CBCT due to partial or complete exclusion from the imaging field of view.
Conclusion
Overall, 4D-CBCT imaging doses are approximately twofold higher than 3D-CBCT, this increase may be clinically justified by improved image quality and respiratory motion information. These findings highlight the importance of imaging protocol optimization to balance IGRT accuracy and patient dose and support the use of RPLGDs as a reliable tool for CBCT dose assessment in thoracic radiotherapy.