• Int. J. Radiat. Oncol. Biol. Phys. · May 2012

    Patient-specific three-dimensional concomitant dose from cone beam computed tomography exposure in image-guided radiotherapy.

    • Emiliano Spezi, Patrick Downes, Richard Jarvis, Emil Radu, and John Staffurth.
    • Department of Medical Physics, Velindre Cancer Centre, Cardiff, United Kingdom. Spezi@wales.nhs.uk
    • Int. J. Radiat. Oncol. Biol. Phys. 2012 May 1; 83 (1): 419-26.

    PurposeThe purpose of the present study was to quantify the concomitant dose received by patients undergoing cone beam computed tomography (CBCT) scanning in different clinical scenarios as a part of image-guided radiotherapy (IGRT) procedures.Methods And MaterialsWe calculated the three-dimensional concomitant dose received as a result of CBCT scans in 6 patients representing different clinical scenarios: two pelvis, two head and neck, and two chest. We assessed the effect that a daily on-line IGRT strategy would have on the patient dose distribution, assuming 40 CBCT scans throughout the treatment course. The additional dose to the planning target volume margin region was also estimated.ResultsIn the pelvis, a single CBCT scan delivered a mean dose to the femoral heads of 2-6 cGy and the rectum of 1-2 cGy. An additional dose to the planning target volume was within 1-3 cGy. In the chest, the mean dose to the planning target volume varied from 2.5 to 5 cGy. The lung and spinal cord planning organ at risk volume received ≤4 cGy and ≤5 cGy, respectively. In the head and neck, a single CBCT scan delivered a mean dose of 0.3 cGy, with bony structures receiving 0.5-0.8 cGy. The femoral heads received an additional dose of 1.5-2.5 Gy. A reduction of 20-30% in the mean dose to the organs at risk was achieved using bowtie filtration. In the head and neck, the dose to the eyes and brainstem was eliminated by decreasing the craniocaudal field size.ConclusionsThe additional dose from on-line IGRT procedures can be clinically relevant. The organ dose can be significantly reduced with the use of appropriate patient-specific settings. The concomitant dose from CBCT should be accounted for and the acquisition settings optimized for optimal IGRT strategies on a patient basis.Copyright © 2012 Elsevier Inc. All rights reserved.

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