The Association Between Radiation Therapy Dose and Overall Survival in Patients With Intracranial Infiltrative Low-Grade Glioma Treated With Concurrent and/or Adjuvant Chemotherapy

ABSTRACT: Purpose Previous trials have shown no benefit for radiotherapy (RT) dose escalation when RT is given as adjuvant monotherapy for infiltrative low grade glioma (LGG). However, the current standard of care for high risk LGG is RT with concurrent and/or adjuvant chemotherapy. The effect of RT dose escalation on overall survival (OS) in the setting of concurrent and/or adjuvant chemotherapy is not well established. Methods and materials We used the National Cancer Database (NCDB) to select records for adult patients with intracranial grade 2 LGG diagnosed between 2004–2015. Patients must have received adjuvant external beam RT with concurrent and/or adjuvant chemotherapy. RT dose level was categorized as standard (45 - 54 Gy) or high (>54 Gy - 65 Gy). Multivariable and propensity score matched analyses were used. Results The study cohort consisted of 1043 patients, of which 644 (62%) received standard dose (median 54 Gy) and 399 (38%) received high dose RT (median 60 Gy). RT dose level was not associated with OS (hazard ratio [HR] 1.2, p=0.1) in multivariable analysis. Propensity score matching yielded 380 matched pairs (n=760). There was no difference in OS for high dose vs. standard dose RT in the matched cohort (5-year OS 64% vs. 69%, p=0.14), nor in the 2 prespecified subgroups of astrocytoma histology and 1p/19q non-codeleted. Conclusions Adjuvant RT dose escalation above 54 Gy in the setting of concurrent and/or adjuvant chemotherapy was not associated with improved OS for patients with infiltrative LGG in this NCDB retrospective study. This was also true for the subgroups with less chemotherapy sensitive disease including astrocytoma histology and 1p/19q non-codeleted, though these analyses were limited by small size. Methods to improve OS other than RT dose escalation in the setting of concurrent and/or adjuvant chemotherapy should be considered for patients with poor prognosis LGG.