Reduced Treatment Volumes for Glioblastoma Associated With Lower Rates of Radionecrosis and Lymphopenia: A Pooled Analysis.

Purpose: There is marked variability in treatment fields for glioblastoma. We performed a retrospective study comparing outcomes of patients treated according to MD Anderson Cancer Center (MDACC) or Radiation Therapy Oncology Group (RTOG) guidelines and identified differences in treatment-related toxicity.

Methods And Materials: Adult patients with glioblastoma treated with surgery and adjuvant radiation treatment were included in this study. Primary outcomes were local control, progression-free survival (PFS), overall survival (OS), and radiation-related toxicity. PFS and OS were estimated using the Kaplan-Meier estimator. Univariate and multivariate analyses were conducted using Cox regression models.

Results: In total, 257 patients met the inclusion criteria with a median age of 60.1 years at diagnosis. There were 162 and 95 patients treated according to the MDACC or RTOG guidelines, respectively. Despite having similar gross tumor volumes, the RTOG cohort had a larger median planning target volume (303.2 cm³ vs 430.7 cm³, < .001) and worse PFS (6 months vs 9 months, = .031). There was no difference in OS between treatment techniques. Patients treated according to RTOG guidelines experienced higher rates of radionecrosis (34% vs 21%, = .024) and severe lymphopenia (15% vs 7%, = .044).

Conclusions: Patients treated according to MDACC guidelines had smaller treatment volumes, improved PFS, and lower rates of radionecrosis and severe lymphopenia. However, when adjusting for prognostic factors, treatment type was not associated with PFS in multivariate analysis. Prospective investigation is warranted to confirm these differences in outcomes.