Does pre-irradiation gross tumor volume predict the risk of progression after radiation therapy in pediatric patients with adamantinomatous craniopharyngioma?

Objective: In a cohort of patients who were treated with resection and adjuvant radiotherapy (RT) for adamantinomatous craniopharyngioma (ACP), the authors aimed to determine whether gross tumor volume (GTV) at the initiation of RT was associated with the risk of progressive disease (PD) following treatment.
Methods: Pediatric and adolescent patients who received surgery and RT for ACP at a single institution from 1998 to 2021 were identified. Univariable Cox regression analyses (UVAs) were performed to assess the association between pre-RT GTV and PD after RT. Multivariable analyses (MVAs) were used to control for potential confounders. Two different endpoints were used to define PD. The first definition was based on radiographic tumor growth, with or without progression of clinical symptoms. The second definition was the requirement for an additional tumor-directed intervention following the completion of RT.
Results: Forty-eight patients were eligible for inclusion. The median age at diagnosis was 7.9 years (range 2.1-17.4 years). All patients were treated with surgery and RT with a median dose of 52.2 Gy (range 45-55.8 Gy) and median GTV of 9.86 cm3 (range 0.7-117.7 cm3). After a median follow-up of 66.4 months, 8 patients experienced PD based on both definitions. The 5-year event-free survival rate was 85.4% (95% CI 74.1%-98.3%). On both UVA and MVA, GTV was significantly associated with an increased likelihood of PD (UVA: HR 1.02, 95% CI 1.00-1.04, p = 0.02; MVA: HR 1.10, 95% CI 1.02-1.19, p = 0.01). However, after exclusion of a single outlier with a GTV of 117.7 cm3 prior to RT (remainder of the cohort: range 0.7-37.3 cm3), a second analysis identified no significant association between GTV and PD (UVA: HR 1.03, 95% CI 0.96-1.10, p = 0.4; MVA: HR 1.06, 95% CI 0.96-1.17, p = 0.24).
Conclusions: The authors conclude that for most children and adolescents with ACP, the GTV at the initiation of RT is not associated with the risk of PD. This finding may influence surgical practice, because it suggests that aggressive tumor debulking for the purpose of improving the efficacy of RT may not be necessary. In the case of giant tumors, however, novel strategies may be needed for tumor control.