Using an on-board cone-beam computed tomography scanner as an imaging modality for gel dosimetry: A feasibility study

On-board cone-beam computed tomography (CBCT) was used to scan the N-isopropylacrylamide (NIPAM) gel dosimeter. A dose-response curve from 1 to 12 Gy was created. The dose profile and depth dose curve were measured, and the dose distribution acquired from CBCT was then compared with that obtained from a treatment planning system (TPS). The linearity of the dose-response curve obtained by CBCT scanning of the NIPAM gel was 0.985. The mean percent standard deviation of various doses was 12.8%. A 12- to 24-h post-irradiation time was required to achieve stable CBCT readouts. Both dose profile and depth dose were in agreement with the results of TPS. The dose difference at the isocenter between CBCT and TPS was 3.8%. The gamma evaluation under the conditions of 5% dose difference and 5 mm distance-to-agreement was performed with the pass rate of 92.6%. These results indicate that an on-board CBCT can be used for scanning gel dosimeters in clinical radiotherapy.