Low Grade Glioma: a Measuring Radiographic Response to Radiotherapy

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 > or = 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.