Low grade glioma: A measuring radiographic response to radiotherapy

Purpose: We set out to determine the rate of response of low-grade (WHO Gra de II) gliomas to radiotherapy and analyze the relationship between radiogr aphic response, symptom control and patient survival. Methods: Patients wer e eligible for this study if they had received radiotherapy for pathologica lly confirmed, residual, supratentorial low-grade astrocytoma, oligodendrog lioma, or mixed glioma, and imaging studies (baseline and follow-up) were a vailable for review. Percent change in tumor size and rate and timing of re sponse were determined by maximum linear measurement, area measurement, vol ume measurement using an ellipsoid model, and volume measurement by image s egmentation. For each method, response to radiotherapy was defined firstly as a greater than or equal to 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 im provement and progression-free survival were analyzed using a Cox Proportio nal 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 a fter surgery. Responses were common and not felt to be due to a steroid eff ect. Use of normalized response criteria improved agreement between assessm ent of response as determined by the 4 methods. Median time to maximum radi ographic 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-gr ade gliomas are moderately radioresponsive. Use of volume measurement may o ver-estimate the number of partial responses unless a volume reduction equi valent to a 50% area decrease is used to define response. The best way to m easure response remains uncertain because neither visual, areal nor volume changes confidently predicted clinical outcomes.