Radiation dose measurements during kilovoltage-cone beam computed tomography imaging in radiotherapy

Objective: The use of image guidance during radiotherapy for accurate localization and setup has become the standard care of practice in radiotherapy. This mostly involves the use of kilovoltage-cone beam computed tomography (kV-CBCT) for verification of patient setup on the first few days and on a weekly basis. Some protocols require this to be performed daily and also before and after the treatment. Though the radiation due to this kV-CBCT is small, the repeated use could deliver a dose that could increase the probability of the stochastic effect. The main purpose of this work is to measure radiation dose during image guidance with kV-CBCT. Materials and Methods: In this work, we have attempted to measure the dose during kV-CBCT for different sites both on a humanoid phantom and on patients undergoing image-guided radiotherapy with MOSFETs calibrated against an ion chamber. Results: The dose measurement on patients during kV-CBCT resulted in mean doses of 0.19 and 0.3 cGy to the ipsilateral and contralateral eyes, 0.625 and 1.097 cGy to the surface of the ipsilateral and contralateral breasts, and 3.01 cGy to the surface of the pelvis. Conclusion: Radiation dose to the eye, breast, and the surface of the pelvis have been arrived at during CBCT. The doses measured on patients agreed closely with those measured on humanoid phantom and with published values.