Program Information
Imaging Dose From Kilovoltage Cone Beam Computed Tomography On a TrueBeam Linear Accelerator in Radiation Therapy
X Pan*, W Bradley , T Ochran , UT Health Science Center at Tyler, Tyler, TX
Presentations
SU-H4-GePD-I-5 (Sunday, July 30, 2017) 4:30 PM - 5:00 PM Room: Imaging ePoster Lounge
Purpose: To measure the imaging dose from kilovoltage cone beam computed tomography (kV CBCT) of a TrueBeam accelerator in radiation therapy.
Methods: Clinical protocols on a TrueBeam accelerator for pelvis (full rotation, “half fan” mode, 125 kVp, 1080 mAs) and head (full rotation, “full fan” mode, 100 kVp, 270 mAs) kV CBCT techniques were assessed. An ArcCheck phantom with the cavity insert was selected for the pelvis protocol, while only the cavity insert of the phantom was used for the head protocol. A farmer chamber connected to a PC ElectrometerTM was used to measure the charge generated during the CBCT scan. Radiation exposure was measured at the center and surface for both protocols. Radiation dose was determined by methods recommended by AAPM’s TG-61 protocol for kilovoltage x-ray beam dosimetry.
Results: The measured average reading was 476.86 pC at the center and 450.82 pC near the surface for pelvis protocol, while it was 164.22 pC at the center and 116.74 pC near the surface for head protocol. The doses were determined to be 2.31 and 2.18 cGy for the pelvis protocol, and 0.79 and 0.56 cGy for the head protocol, respectively. For a 44-fraction prostate treatment course, daily CBCT imaging would contribute an additional 1.02 Gy to the center and 0.96 Gy near the surface of the patient. For a 35-fraction head and neck treatment course, daily CBCT imaging would contribute an additional 0.28 Gy to the center and 0.20 Gy near the surface of the patient.
Conclusion: This work shows that the dose from a clinical kV CBCT scan ranges from 0.79 to 2.31 cGy at the center and from 0.56 to 2.18 cGy near the surface. Daily CBCT imaging radiation dose can be taken into account during treatment planning for cancer patients.
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