comparison study of radiation dose received during cone beam computerized tomography and portal imaging techniques

ABSTRACT

Although widely varied in modality and method, all radiographic guidance techniques have one thing in common; they can give a significant radiation dose to the patient; which may have a late radiation stochastic effect on normal body tissues. To quantify and compare radiation doses to the tumour and the surrounding critical organs resulting from the orthogonal pair portal and megavoltage cone beam computarized tomography [MV CBCT] imaging techniques. The dose to the patient resulting from the orthogonal pair and the MV CBCT imaging techniques, has been calculated based on a 6 MV Oncor linear accelerator equipped with an amorphous silicon flat panel. All calculations were done on Eclipse 3D treatment planning system. 18 patients representing three different treatment sites [head and neck, thorax, and pelvis] were analysed. Data from 6 patients for each treatment site were used to calculate the mean doses. Calculations were done for The integral dose, maximum dose to the patient, dose at the isocenter, and mean dose to the tumour and each critical organ. The absolute dose measured as integral dose, maximum dose to the patient, dose at the isocenter, and mean dose to the tumour and each critical organ was higher for MV CBCT as compared to orthogonal pair technique for all treatment sites. For both techniques, the absolute dose was higher for head and neck and thorax as compared to pelvis. The difference of maximum dose to the patient showed greater variation for head and neck, but not for thorax and pelvis. There are relatively high dose regions generated by MV CBCT that occur inside critical organs as well treatment area and tend to be larger than those generated by the orthogonal pair technique