Table 1.

Characteristics of studies included in the meta-analysis.

Study	Year	Language	Control source	Number of patients in radiotherapy group	Number of healthy controls in control group
Luo et al. [14]	2004	English	Healthy controls	76	25
Zhao et al. [15]	2007	Chinese	Healthy controls	23	21
Qiu et al. [16]	2007	English	Healthy controls	21	10
Li et al. [17]	2011	Chinese	Healthy controls	28	10