Radiation dose from cone beam computed tomography for image-guided radiation therapy.
OBJECTIVE
To perform a comprehensive study on organ absorbed doses and effective doses from cone beam computed tomography (CBCT) for three different treatment sites.


METHODS
An extensive set of dosimetric measurements were performed using a widely used CBCT system, the On-Board Imager (OBI). Measurements were performed using a female anthropomorphic phantom with thermoluminescent dosimeters (TLD). The effective doses to the body and the absorbed doses to 26 organs were reported using two different technical settings, namely, the standard mode and the low-dose mode. The measurements were repeated for three different scan sites: head and neck, chest, and pelvis. Comparisons of patient doses as well as image quality were performed among the standard mode CBCT, low-dose mode CBCT, and fan beam CT.


RESULTS
The mean skin doses from standard mode CBCT to head and neck, chest and pelvis were 6.7, 6.4, and 5.4 cGy per scan, respectively. The effective doses to the body from standard mode CBCT for imaging of head and neck, chest, and pelvis were 10.3, 23.7, and 22.7 mSv per scan, respectively. Patient doses from low-dose mode CBCT were approximately one fifth of those from standard mode CBCT.


CONCLUSIONS
Patient position verification by standard mode CBCT acquired by OBI on a daily basis could increase the secondary cancer risk by up to 2% to 4%. Therefore lower mAs settings for daily CBCT should be considered, especially when bony anatomy is the main interest.
Kan
Monica W K
MW
Department of Oncology, Princess Margaret Hospital, Hong Kong SAR, China. kanwkm@ha.org.hk
Leung
Lucullus H T
LH
Wong
Wicger
W
Lam
Nelson
N
D002138:Calibration; D054893:Cone-Beam Computed Tomography; D005260:Female; D006257:Head; D006801:Humans; D009333:Neck; D010315:Particle Accelerators; D010388:Pelvis; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal; D050397:Radiotherapy, Intensity-Modulated; D013819:Thermoluminescent Dosimetry / Q000379:methods*