paediatrics Brussels 17

Impact of Radiation Boost on Intelligence in Medulloblastoma

Table 2. CSR Dose and Boost Volume

Total Patients

Intercept

Slope

Index

No.

Mean

SE

Comparison P

Estimate SE Estimate SE

P

Comparison P

FSIQ

Growth curve analysis Reduced TB boost Reduced PF boost Standard TB boost Standard PF boost Single–time point analysis

93.02 3.53 97.29 2.86 101.24 5.19 95.78 1.90

1.12 2.18 2.96 2.05

1.55 0.88 2.78 0.54

.39 .01 .23

.04 .19 .04† .04 .78 .89† .19 .78 .75†

19 27

91.97 4.22 .13 .31 .11 83.93 2.57 .13 .75 .87 84.98 8.35 .31 .75 .55 82.90 2.00 .11 .87 .55

7

.001 .04 .89 .75†

49

.06

—

Reduced TB boost All other treatments

8

91.25 6.17 78.65 2.17

— — — — — — — — — —

65

PSI

Growth curve analysis Reduced TB boost All other treatments Single–time point analysis

.75

.45

18 80

83.07 4.29 80.41 1.26

90.74 3.40 92.63 1.71

1.14 2.38

1.63 0.38

.47

.001

.07

—

Reduced TB boost All other treatments

5

89.20 6.81 76.11 2.02

— — — — — — — — — —

57

PRI

Growth curve analysis Reduced TB boost All other treatments Single–time point analysis

.07

.03

19 89

95.95 4.49 85.30 1.62

96.17 3.49 98.56 1.73

1.40 2.20

1.64 0.46

.38

.001

.096

—

Reduced TB boost All other treatments

8

92.50 6.43 80.98 2.27

— — — — — — — — — —

64

WMI

Growth curve analysis Reduced TB boost All other treatments Single–time point analysis

.40

.18

18 81

93.04 5.15 87.37 1.56

96.02 3.66 99.75 1.87

0.30 2.15

1.82 0.45

.86

.001

.04

—

Reduced TB boost All other treatments

5 100.20 7.72

— — — — — — — — — —

59

83.31 2.25

VCI

Growth curve analysis Reduced TB boost All other treatments Single–time point analysis

.27

.14

20 87

93.66 3.83 87.24 1.36

95.04 3.14 96.39 1.57

0.64 1.48

1.42 0.39

.64

.001

.12

—

Reduced TB boost All other treatments

8

93.50 5.61 84.03 1.97

— — — — —

65 — — — — — 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.

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

1763

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