Actigraphic measures
Sleep estimates were assessed using a wrist-worn actigraph (type wGT3XBT, Pensacola, FL). This device registers the occurrence and the intensity of arm movements and distinguishes the wake state from sleep. This low-cost measurement has been validated against polysomnography, and is well-tolerated during this intense stage of cancer therapy26. Participants were instructed to wear the actigraph for seven days and seven nights. Also, they were asked to keep a sleep log, to facilitate correct interpretation of the data.
The actigraphy software ActiLife (version 6.13.4, Sadeh algorithm) and the sleep- and wake times from the sleep log were used to process the actigraph data and calculate sleep outcomes. Sleep outcomes were only calculated if there were available recordings of at least five nights, as this is advised to obtain reliable actigraphic measures27. The following outcomes were obtained: sleep efficiency (SE; ratio between the time spent in bed and the total sleep time), sleep onset latency (SOL; number of minutes between bedtime and onset of sleep), wake after sleep onset (WASO; number of minutes awake after the onset of sleep), total sleep time (TST), total time spent in bed (TIB) and number of awakenings (NA). Norm data of 47 healthy Dutch children within the same age range were used to compare actigraphic sleep outcomes28.