Measurement of field match lines in electron beam radiotherapy using carbon quantum dot sheeting enhanced Cherenkov imaging

The aim of this study is to test the utility of optical imaging technique that contains a flexible carbon quantum dot (cQD) sheet and optical camera to measure matching of adjacent radiation fields due to introduced distances delivered during electron radiotherapy treatments. Aqueous solution of cQD is prepared with distilled water at the concentration of 0.1 g/L and the cQD sheet is prepared by spin coating and UV curing with the same concentration. All experiments are performed on the Varian VitalBeam system and optical emission is captured at source to surface distance (SSD) of 100 cm using a tripod mounted camera (Andor iXon ultra-888). The results demonstrate that the captured optical intensity is linear with delivered dose, almost independent of energy and dose rate. The profile in x and y axis show agreement with defined field sizes using maximum slope profile estimate measurement of <3.5 mm. The results of random tests also show that the differences between the measured field match distances calculated by match amplitude of optical imaging and the actual settings are all less than 1.3 mm. This work demonstrated that the optical imaging technique which consist of flexible cQD sheet and optical camera has potential to detect and quantify the field match line in surface tissue during electron beam radiotherapy.