Table 1.
Baseline characteristics of included studies
| References | Country | Design | Study period | WHO criteria | Simpson grade | No. of patients | |
|---|---|---|---|---|---|---|---|
| Adjuvant RT | Observation | ||||||
| Condra et al. [28] | USA | R, OS, 1 institution | 1964–1992 | 1993 | 1,2,3 | 4 | 21 |
| Aghi et al. [44] | USA | R, OS, 1 institution | 1993–2004 | NR | 1 | 8 | 100 |
| Jo et al. [29] | Korea | R, OS, 1 institution | 1997–2008 | 2000 | 1 | 19 | 13 |
| Yu et al. [43] | China | R, OS, 1 institution | 2003–2008 | NR | 1,2,3 | 47 | 11 |
| Komotar et al. [9] | USA | R, OS, 1 institution | 1992–2011 | 1993 | 1,2 | 13 | 32 |
| Lee et al. [30] | USA | R, OS, 1 institution | 1999–2009 | 2007 | 1,2,3 | 17 | 54 |
| Park et al. [10] | Korea | R, OS, 1 institution | 1997–2011 | 2000/2007 | 1,2,3 | 17 | 38 |
| Aizer et al. [11] | USA | R, OS, 1 institution | 1997–2011 | NR | 1,2,3 | 18 | 50 |
| Sun et al. [45] | USA | R, OS, 1 institution | 1993–2012 | 2007 | 1,2,3 | 39 | 112 |
| Yoon et al. [12] | USA | R, OS, 2 institutions | 2000–2010 | 2000 | 1,2,3 | 7 | 102 |
| Wang et al. [26] | Taiwan | R, OS, 1 institution | 2001–2009 | 2007 | GTR | 3 | 11 |
| Jenkinson et al. [7] | UK | R, OS, 3 institutions | 2001–2010 | 2000/2007 | 1,2,3 | 32 | 81 |
| Yip et al. [32] | Taiwan | R, OS, 1 institution | 2005–2014 | NR | TR | 7 | 16 |
| Endo et al. [31] | Japan | R, OS, 1 institution | 2000–2013 | 2007 | 1,2 | 11 | 19 |
| Bagshaw et al. [13] | USA | R, OS, 1 institution | 1991–2014 | 2007 | 1,2,3 | 12 | 40 |
| Graffeo et al. [14] | USA | R, OS, 1 institution | 1988–2011 | 2016 | 1,2,3 | 8 | 61 |
| Dohm et al. [34] | USA | R, OS, 1 institution | 1993–2014 | 2007 | 1,2,3 | 12 | 37 |
| Alghamdi et al. [3] | Canada | R, OS, 1 institution | 2003–2013 | NR | GTR | 1 | 43 |
| Cho et al. [33] | Korea | R, OS, 1 institution | 2003–2014 | 2000/2007 | 1,2 | 13 | 16 |
| Shakir et al. [36] | Canada | R, OS, 1 institution | 1992–2013 | 2007 | 1,2,3 | 12 | 28 |
| Chen et al. [15] | USA | R, OS, 1 institution | 1993–2014 | 1993/2000/2007 | 1,2,3 | 10 | 104 |
| Budohoski et al. [35] | UK | R, OS, 3 institutions | 2007–2014 | 2016 | 1,2,3 | 35 | 108 |
| Zeng et al. [40] | China | R, OS, SEER data | 2008–2015 | 2007 | 1,2,3 | 194 | 533 |
| Zhi et al. [41] | USA | R, OS, 1 institution | 2000–2012 | 2000/2007 | 1,2,3 | 26 | 72 |
| Wang et al. [39] | USA | R, OS, 1 institution | 2009–2018 | 2016 | 1,2,3 | 71 | 142 |
| Lee et al. [16] | Korea | R, OS, 1 institution | 2000–2013 | 2007 | 1,2,3 | 20 | 24 |
| Ros-Sanjuan et al. [38] | Spain | R, OS, 1 institution | 1994–2014 | 2016 | 1 | 5 | 5 |
| Li et al. [37] | China | R, OS, 1 institution | 2008–2015 | NR | 1,2 | 50 | 151 |
| Lee et al. [42] | USA | R, OS, 1 institution | 2000–2015 | 2000/2007 | 1,2,3 | 18 | 133 |
| Jiang 2020 [27] | China | R, OS, 1 institution | 2008–2016 | 2007 | 1,2 | 8 | 10 |
R, retrospective; OS, observational study; WHO, World Health Organization; GTR, gross total resection; RT, radiotherapy; SEER, Surveillance, Epidemiology, and End Results; NR, not reported