Effectiveness of spiritual interventions on psychological outcomes and quality of life among paediatric patients with cancer: a study protocol for a systematic review oleh Ka Yan Ho, Katherine Ka Wai Lam, Qi Liu, Hammoda Abu-Odah, Jacqueline Mei Chi Ho, Winsome Lam, Polly Ma, Getaneh Mulualem Belay, Dong-Lan Ling, Shirley-Siu-Yin Ching, Frances-Kam-Yuet Wong