Correlation between initial tumor enlargement and magnetic resonance imaging characteristics following linear accelerator-based stereotactic radiosurgery for acoustic neuromas.

Abstract

Initial tumor enlargement (or pseudoprogression) instead of true tumor progression is acommon phenomenon in patients with acoustic neuromas who are treated with stereotactic radiosurgery (SRS). This phenomenon can affect clinical decision-making and patient management. This study assessed the correlation between initial tumor enlargement and magnetic resonance imaging characteristics in patients with acoustic neuromas who were treated with linear accelerator (LINAC)-based SRS. The long-term tumor control outcomes were also analyzed. In total, 330 patients with sporadic acoustic neuromas who were treated with LINAC SRS between March 2006 and March 2020 were retrospectively evaluated to assess their initial tumor enlargement. The tumors were divided into homogeneously enhanced, heterogeneously enhanced, and cystic types based on the morphological characteristics noted on magnetic resonance images. Tumor control was assessed in 275 patients with afollow-up duration of more than 2years. Initial enlargement was observed in 137 of 330 (41.5%) tumors as early as 3months after LINAC SRS. Data analysis revealed that postoperative tumors with aresidual volume lower than 2.5 cm3 had alower incidence of initial enlargement (p = 0.039). No correlation was noted between the initial enlargement and morphological characteristics of tumors. In patients with amean follow-up duration of 82.8 ± 37.2months, heterogeneously enhanced tumors exhibited alower control rate than homogeneously enhanced and cystic tumors (p = 0.045). No correlation was noted between initial enlargement and tumor control. Initial enlargement can occur as early as 3months after SRS. Postoperative residual tumors with avolume lower than 2.5 cm3 exhibit alower incidence of initial enlargement. Heterogeneously enhanced tumors have alower local control rate.