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


RESULTS
In 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.


CONCLUSIONS
The 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.
Department of Medical Physics, Velindre Cancer Centre, Cardiff, United Kingdom. Spezi@wales.nhs.uk
Emiliano
E
Spezi
Patrick
P
Downes
Richard
R
Jarvis
Emil
E
Radu
John
J
Staffurth
D001933:Brain Stem / Q000000981:diagnostic imaging / Q000528:radiation effects; D054893:Cone-Beam Computed Tomography / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D005123:Eye / Q000000981:diagnostic imaging / Q000528:radiation effects; D005270:Femur Head / Q000000981:diagnostic imaging / Q000528:radiation effects; D006257:Head / Q000000981:diagnostic imaging / Q000528:radiation effects; D006321:Heart / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects; D009010:Monte Carlo Method; D009333:Neck / Q000000981:diagnostic imaging / Q000528:radiation effects; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects*; D010388:Pelvis / Q000000981:diagnostic imaging / Q000528:radiation effects; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control*; D061089:Radiotherapy, Image-Guided / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000528:radiation effects