Evaluasi Dosis Tambahan dari Cone Beam Computed Tomography (CBCT) pada Image Guided Radiotherapy (IGRT) Kasus Kanker Head and Neck, Payudara, dan Pelvis

Cone Beam CT (CBCT) is an imaging system used to verify the position in Image Guided Radiotherapy (IGRT). CBCT uses wide-cone beam radiation, which is wider than that of a regular CT Scan. Therefore, an evaluation of the dose associated with CBCT use in IGRT is necessary. This study aims to measure the CBCT output dose, analyze the CBCT dose addition to the radiotherapy patient dose, and provide recommendations for the use of CBCT in radiotherapy. The CBCT dose parameter evaluated was CBDIw, measured on a CTDI phantom with a diameter of 16 cm for head and neck and 32 cm for breast and pelvis, using a 100 mm pencil ion chamber dosimeter from PTW Nomex. Three CBCT protocols, fast head and neck CW S20, Breast Left S20 CW, and Pelvis L20, were evaluated. The dose addition analysis was carried out in three cancer cases: breast, head and neck, and pelvis, each with 10 patients. The CBDIw value for the Pelvis L20 protocol is the highest at 24.7 mGy; Breast Left S20 CW is 14.3 mGy; and Fast Head and Neck S20 is 0.7 mGy. In head & neck cancer cases, the use of the breast left S20 CW protocol contributes to a cumulative increase in the mean body dose of up to 12.85%. The use of the L20 pelvis protocol in each fraction in breast cancer cases results in a dose increase of up to 7.91% and in pelvic cancer cases results in a dose increase of up to 7.59%. Optimization of protocol selection and CBCT frequency should be adjusted individually for each patient based on clinical characteristics, while also considering image quality, especially in pediatric patients who are vulnerable to radiation. Keywords: Cone Beam CT (CBCT), CBDI, additional dose, radiotherapy