Variation of patient imaging doses with scanning parameters for linac-integrated kilovoltage cone beam CT

Abstract

Abstract. To evaluate the Elekta kilovoltage CBCT doses and the associated technical protocols with patient dosimetry estimation. Image guidance technique with cone-beam CT (CBCT) in radiation oncology on a daily basis can deliver a significant dose to the patient. To evaluate the patient dose from LINAC-integrated kV cone beam CT imaging in imageguided radiotherapy. CT dose index (CTDI) were measured with PTW TM30009 CT ion chamber in air, in head phantom and body phantom, respectively; with different combinations of tube voltage, current, exposure time per frame, collimator and gantry rotation range. Dose length products (DLP) were subsequently calculated to account for volume integration effects. The CTDI and DLP were also compared to AcQSim™ simulator CT for routine clinical protocols. Both CTDI air and CTDI w depended quadratically on the voltage, while linearly on milliampere x seconds (mAs) settings. It was shown that CTDI w and DLP had very close relationship with the collimator settings and the gantry rotation ranges. Normalized CTDI w for Elekta XVI™ CBCT was lower than that of ACQSim simulator CT owing to its pulsed radiation output characteristics. CTDI w can be used to assess the patient dose in CBCT due to its simplicity for measurement and reproducibility. Regular measurement should be performed in QA & QC program. Optimal image parameters should be chosen to reduce patient dose during CBCT.

Evaluation of the relationship between phantom position and computed tomography dose index in cone beam computed tomography when assuming breast irradiation

“…Although the effective dose does not represent the exposure of an individual patient, it is useful for comparing doses from different examinations 16 . Consequently, Liao et al measured CTDI w in CBCT and calculated DLP from the CTDI w 17 . Moreover, Abuhaimed et al reported that DLP is useful for comparing patient doses between diagnostic CT and CBCT in radiation therapy 18 .…”

“…16 Consequently, Liao et al measured CTDI w in CBCT and calculated DLP from the CTDI w . 17 Moreover, Abuhaimed et al reported that DLP is useful for comparing patient doses between diagnostic CT and CBCT in radiation therapy. 18 This study calculated DLP by multiplying the CTDI w by the x-ray beam width in a longitudinal direction.…”