Background/aim: We report the analysis of ketamine doses needed and the recovery times in pediatric oncology patients undergoing repeated radiotherapy sessions. Materials and methods: In a single-blind prospective study design, thirty-three pediatric patients undergoing radiotherapy due to oncologic disorders received 2 mg/kg ketamine and 10 μg/kg atropine intravenously and the rescue drug to be administered was ketamine at 0.5 mg/kg when the sedation level was inadequate. Total ketamine consumption, additional doses, and recovery time were recorded. Results: Data of 635 consecutive radiotherapy sessions were evaluated. There was no significant alteration in total ketamine consumption required to complete the radiotherapy periods during consecutive procedures (P > 0.05). However, the recovery times started to decrease by the fourth session (P = 0.02) and continued to decrease onwards during the whole study period (P = 0.001). The mean of the first recovery time was 13.68 ± 3.99 min, whereas the mean of the last recovery time was 7.66 ± 6.35 min. Conclusion: A requirement for an incremental increase in ketamine dose after subsequent administrations was not detected, despite a significant decrease in recovery times being anticipated when ketamine is used repeatedly for sedative purposes in consecutive radiotherapy sessions.