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Low Grade Glioma: A Measuring
Radiographic Response to Radiotherapy
Glenn Bauman, Peter Pahapill, David
Macdonald, Barbara Fisher, Christopher Leighton, Gregory Cairncross
From the Departments of
Oncology (G.B., D.M., B.F., C.L., G.C.) and Clinical Neurological
Sciences (P.P., D.M., G.C.), University of Western Ontario, and London
Regional Cancer Centre (G.B., D.M., B.F., C.L., G.C.), London,
Ontario. RECEIVED APRIL 9, 1998. ACCEPTED IN FINAL FORM JULY 15, 1998.
Reprint requests to: Glenn Bauman, Department of Radiation Oncology,
London Regional Cancer Centre, 790 Commissioners Road, East, London,
Ontario, Canada N6A 4L6.
Purpose. We
set out to determine the rate of response of low-grade (WHO Grade II)
gliomas to radiotherapy and analyze the relationship between
radiographic response, symptom control and patient survival.
Methods.
Patients were eligible for this study if they had received
radiotherapy for pathologically confirmed, residual, supratentorial
low-grade astrocytoma, oligodendroglioma, or mixed glioma, and imaging
studies (baseline and follow-up) were available for review.
Percent change in tumor size and
rate and timing of response were determined by maximum linear
measurement, area measurement, volume measurement using an ellipsoid
model, and volume measurement by image segmentation.
For each method, response to
radiotherapy was defined firstly as a = 50% decrease in tumor size
(partial response), and secondly as a decrease equivalent to a 50%
area decrease (normalized partial response).
Relationships between radiographic
response, clinical improvement and progression-free survival were
analyzed using a Cox Proportional Hazard's model.
Results.
Twenty-one patients in a database (13 male, 8 female; ages 22-66
years) met the eligibility criteria.
Twenty were imaged by computed
tomography, 18 had an astrocytoma and 15 were irradiated soon after
surgery.
Responses were common and not felt
to be due to a steroid effect.
Use of normalized response criteria
improved agreement between assessment of response as determined by the
4 methods.
Median time to maximum radiographic
improvement was 2.8 months (range, 1.5-11).
Sixteen patients (76%) were
improved neurologically, the median time to progression was 4.8 years
and the 5-year progression-free survival rate was 43%.
We did not detect a statistically
significant association between response (as measured by any method),
symptomatology and progression-free survival.
Conclusions.
Low-grade gliomas are moderately radioresponsive.
Use of volume measurement may
over-estimate the number of partial responses unless a volume
reduction equivalent to a 50% area decrease is used to define
response.
The best way to measure response
remains uncertain because neither visual, area, nor volume changes
confidently predicted clinical outcomes.
Copyright © Canadian Journal of
Neurological Sciences. All rights reserved.
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