Evaluation of dynamic tumour tracking radiotherapy with real-time monitoring for lung tumours using a gimbal mounted linac

Abstract Purpose To evaluate feasibility and acute toxicities after dynamic tumour tracking (DTT) irradiation with real-time monitoring for lung tumours using a gimbal mounted linac. Materials and methods Spherical gold markers were placed around the tumour using a bronchoscope prior to treatment planning. Prescription dose at the isocentre was 56Gy in 4 fractions for T2a lung cancer and metastatic tumour, and 48Gy in 4 fractions for the others. Dose-volume metrics were compared between DTT and conventional static irradiation using in-house developed software. Results Of twenty-two patients enrolled, DTT radiotherapy was successfully performed for 16 patients, except 4 patients who coughed out the gold markers, one who showed spontaneous tumour regression, and one where the abdominal wall motion did not correlate with the tumour motion. Dose covering 95% volume of GTV was not different between the two techniques, while normal lung volume receiving 20Gy or more was reduced by 20%. A mean treatment time per fraction was 36min using DTT. With a median follow-up period of 13.2months, no severe toxicity grade 3 or worse was observed. Conclusions DTT radiotherapy using a gimbal mounted linac was clinically feasible for lung treatment without any severe acute toxicity.