The quality of evidence is downgraded by study limitations (unclear allocation concealment and lack of blinding), by inconsistency (variability in results), and by imprecise results (wide confidence intervals).
A Cochrane review [Abstract] 1 included 9 studies with a total of 2 406 subjects with glioma (low-grade glioma in 7 studies and grade 3 glioma in 2 studies). Meta-analysis was not possible due to differences in interventions and outcomes.
Radiotherapy versus no adjuvant treatment (2 observational studies): At the 12-year follow-up, the risk of cognitive impairment was greater in the radiotherapy group (RR 1.95, 95% CI 1.02 to 3.71; 1 study, n=65); at 5 to 6 years the difference was not statistically significant (RR 1.38, 95% CI 0.92 to 2.06; 1 study, n=195). In the other study, one subject in the radiotherapy group had cognitive impairment at 2 years compared with none in the control group.In one study the radiotherapy group was reported to have had significantly worse mean neurocognitive scores on some tests compared with no radiotherapy, and in the second study, there were no clear differences in any of the various cognitive outcomes at 2 years (n=31) and 4 years (n=15).
Radiotherapy versus chemotherapy (1 RCT): There was no clear difference between study groups in cognitive impairment at up to 3 years (RR 1.43, 95% CI 0.36 to 5.70; 1 study, n=117).High-dose radiotherapy versus low-dose radiotherapy (only 1 of 2 studies reporting this comparison contributed data): at 2 and 5 years there were no clear differences between high- and low-dose radiotherapy arms.Conventional radiotherapy versus stereotactic conformal radiotherapy (1 study involving younger people contributed limited data from the subgroup aged 16 to 25 years): There was no clear difference in the numbers of participants with neurocognitive impairment at 5 years after treatment between conventional arm and stereotactic conformal radiotherapy arm (2/12 vs. 0/11; RR 4.62, 95% CI 0.25 to 86.72; 1 study, n=23).Chemoradiotherapy versus radiotherapy (3 RCTs): One study defined cognitive impairment as a decline of more than 3 points in MMSE score compared with baseline and reported data from 2-year (n=110), 3-year (n=91), and 5-year (n=57) follow-up with no clear difference between the 2 groups. A second study measured MMSE scores over 5 years (n=126 at 2 years, n=110 at 3 years, n=69 at 4 years and n=53 at 5 years), and concluded that there was no difference in MMSE scores between the two study groups (P = 0.4752).Two studies reported quality of life (QoL) outcomes: 1 study reported no differences in Brain-QoL scores between study arms over a 5-year follow-up period, and the other study reported that the long-term results of health-related QoL showed no difference between the groups.
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