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complications (ie, hydrocephalus, other neurologic complications, and mut-
ism alone). The mixed-model technique can handle unbalanced and missing
data, a common phenomenon in clinical samples, and can account for the
different times since diagnosis assessments were conducted.
27
Linear and
curvilinear (ie, quadratic) models were generated for all indices of intellectual
functioning, and the curvilinear model was reported when both models were
significant. (A significant curvilinear term reflects curvature in the slope of the
modeled function representing change over time; for indices that decline over
time, it indicates that the rate of decline from year to year decreases as time
increases.) The intercept produced by the model estimates group functioning
at the beginning of the modeled time period, which was shortly after tumor
resection in our sample. This mixed-model technique was applied using the
PROC MIXED procedure in SAS software (version 9.1; SAS Institute, Cary,
NC). In mixed-model approaches, single–time point data were included,
because these contribute to overall groupmeans and add stability to the overall
model but do not contribute to slope. Furthermore, a univariable analysis was
conducted to examine intellectual outcome as a function of radiation dose and
volume at a single time point, approximately 5 years after diagnosis. For all
analyses, results were considered significant if
P
.05. Finally, a Kaplan-Meier
survival plot was generated to display overall survival for patients separated by
treatment group. Because our groups did not correspond to specific treatment
arms, the plot was not used for statistical analysis.
RESULTS
Patient and Sample Cohort Comparisons
First, we compared patients treated before and after 1995 on
factors that might contribute to cognitive risk. The cohorts did not
differ in age at diagnosis (
P
.72), rate of hydrocephalus requiring
CSF diversion (
P
.95), or mutism (
P
.08). Patients treated
before 1995 had a longer average time from diagnosis to first
Table 2.
CSR Dose and Boost Volume
Index
Total Patients
Intercept
Slope
No.
Mean
SE
Comparison
P
Estimate SE Estimate SE
P
Comparison
P
FSIQ
Growth curve analysis
Reduced TB boost
19
91.97 4.22 .13 .31 .11
93.02 3.53
1.12
1.55
.39
.04 .19 .04†
Reduced PF boost
27
83.93 2.57 .13 .75 .87
97.29 2.86
2.18
0.88
.01
.04 .78 .89†
Standard TB boost
7
84.98 8.35 .31 .75 .55
101.24 5.19
2.96
2.78
.23
.19 .78 .75†
Standard PF boost
49
82.90 2.00 .11 .87 .55
95.78 1.90
2.05
0.54
.001 .04 .89 .75†
Single–time point analysis
.06
—
Reduced TB boost
8
91.25 6.17
— — — — —
All other treatments
65
78.65 2.17
— — — — —
PSI
Growth curve analysis
.75
.45
Reduced TB boost
18
83.07 4.29
90.74 3.40
1.14
1.63
.47
All other treatments
80
80.41 1.26
92.63 1.71
2.38
0.38
.001
Single–time point analysis
.07
—
Reduced TB boost
5
89.20 6.81
— — — — —
All other treatments
57
76.11 2.02
— — — — —
PRI
Growth curve analysis
.07
.03
Reduced TB boost
19
95.95 4.49
96.17 3.49
1.40
1.64
.38
All other treatments
89
85.30 1.62
98.56 1.73
2.20
0.46
.001
Single–time point analysis
.096
—
Reduced TB boost
8
92.50 6.43
— — — — —
All other treatments
64
80.98 2.27
— — — — —
WMI
Growth curve analysis
.40
.18
Reduced TB boost
18
93.04 5.15
96.02 3.66
0.30
1.82
.86
All other treatments
81
87.37 1.56
99.75 1.87
2.15
0.45
.001
Single–time point analysis
.04
—
Reduced TB boost
5 100.20 7.72
— — — — —
All other treatments
59
83.31 2.25
— — — — —
VCI
Growth curve analysis
.27
.14
Reduced TB boost
20
93.66 3.83
95.04 3.14
0.64
1.42
.64
All other treatments
87
87.24 1.36
96.39 1.57
1.48
0.39
.001
Single–time point analysis
.12
—
Reduced TB boost
8
93.50 5.61
— — — — —
All other treatments
65
84.03 1.97
— — — — —
Abbreviations: FSIQ, Full Scale Intelligence Quotient; PF, posterior fossa; PSI, Processing Speed Index; TB, tumor bed; VCI, Verbal Comprehension Index; WMI,
Working Memory/Freedom From Distractibility Index.
Mean comparison.
†Slope comparison.
Impact of Radiation Boost on Intelligence in Medulloblastoma
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