Radiation dose response for supratentorial low-grade glioma--institutional experience and literature review

Purpose: To examine radiation dose response for low-grade glioma (LGG) based on our institutional experience and to review the literature on this topic. Methods and Materials: Sixty-seven patients with supratentorial low-grade nonpilocytic astrocytomas (n=36) or oligodendrogliomas (n=31) were treated with postoperative radiation therapy (RT). Twenty-seven patients (group A) received 5520 cGy; 24 patients (group B) received 5940 cGy; and 16 patients (group C) received 6375 cGy. The corresponding median follow-up was 60, 35 and 91 months, respectively. Results: The disease-specific survival (DSS) at 5 and 10 years were 90.2% and 56.2%, 67.6% and 47.3%, and 62.5% and 50% for groups A, B and C, respectively (P=0.40). Only a greater extent of surgical resection and absence of contrast enhancement predicted DSS on multivariate analyses. Patients receiving higher doses of RT had higher complication rates. Conclusion: Our data confirmed the lack of radiation dose response for supratentorial LGG as demonstrated in the previous randomized trials. The radiation dose should not exceed 5520 cGy because dose escalation did not result in an improvement of DSS and it also increased the complication rates. Future research should focus on the eradication of radioresistant clones either by the improvement of surgical resection or the use of cytotoxic agents that can target on the radioresistant tumor cells.