Cancer is one of the major causes of death in pediatric population. In Hong Kong, 46 patients aged 0 - 19 died from cancer in 2016. Childhood cancer is not common. According to Hong Kong Cancer Registry, there are approximately 190 newly diagnosed cases of childhood cancer each year. Despite this figure is not as high as that in adults, childhood cancer remains a significant concern in healthcare system because of its damaging impacts on children's physical and psychological functions throughout their lifespan. Particularly, children surviving cancer still have to pay a high price for numerous sequelae, notwithstanding their treatment is completed after months and even years.

One of the most prevalent symptoms reported by patients surviving cancer is sleep disturbance. A systematic review indicates 25 - 59 % adults reporting sleep disturbance after their treatment for cancer. A retrospective cohort study in the West also pointed out that 16.7% of childhood cancer survivors complained of disrupted sleep. The causes of sleep disturbance are multifactorial. However, it can largely be attributed to disruption of circadian rhythm by prolonged use of medications and longterm hospitalization. In fact, experiencing sleep disturbance can be devastating for survivors of cancer. Previous literature indicates that sleep disturbance precipitates inflammation and oxidative stress, which are known to be a contributing factor of neurocognitive impairment. Sleep disturbance can also lead to fatigue, which in turn limits patients' capacity in engaging in daily activities and even results in depression, severely compromising patients' quality of life in the long run. In this regard, healthcare professionals, particularly oncology nurses should bear unshrinkable responsibility to intervene this symptom with appropriate interventions, with an aim of improving the survivors' sleep quality and quality of life. Having a reliable and valid instrument that can precisely assess the problem of sleep disturbance of cancer survivors is therefore crucial for the development and evaluation of the intervention.

The Pittsburgh Sleep Quality Index (PSQI) is the most commonly used instrument to assess sleep disturbance. Although this instrument was originally developed to collect subjective information about sleep habits of psychiatric patients, it has been translated into different languages, and has been extensively applied in studies on adult cancer survivors. The results of these studies generally support this instrument to be reliable and valid in assessing sleep disturbance for this group of population. Despite the growing popularity of using this instrument in adults, no studies has so far been conducted to validate the PSQI in the pediatric population, thus limiting its usefulness for children and adolescents. In fact, a comprehensive review of the literature indicated that no validated instrument is currently available for assessing sleep disturbance of childhood cancer survivors, especially in the Hong Kong Chinese context. This lack of validated instruments precludes us from understanding the severity of the problem. Also, it hinders the development of appropriate interventions that promote sleep quality.