Significance of Early Proton Beam Therapy Initiation in Achieving Complete Response in Pediatric Medulloblastoma: A Retrospective Study

ABSTRACT Introduction Proton beam therapy (PBT) has proven to be highly effective in treating pediatric medulloblastoma, offering both excellent therapeutic outcomes and reduced side effects. However, factors influencing tumor response following PBT remain poorly defined, including the optimal interval time between surgery and PBT initiation (ISP). Methods This retrospective study analyzed data from 52 patients with postoperative residual medulloblastoma treated with PBT, focusing on the correlation between tumor response and ISP, as well as other variables associated with achieving complete response (CR). Results The median follow‐up period was 12.5 months (5.3–20.3 months). Treatment response was assessable in all patients, with 26 (50.00%) patients in CR, 15 (28.85%) patients in partial response (PR), and 11 (21.15%) patients with stable disease (SD). Patients who initiated PBT within 31 days post‐surgery had a markedly higher CR rate (74.07%), while those with longer ISPs were more likely to exhibit PR (32.00%) or SD (44.00%). An improved tumor response was significantly associated with a shorter ISP (30.15 ± 5.31 days, p  < 0.001). Univariate logistic regression identified Chang staging M3 (Odds ratio [OR] = 0.103, p  = 0.046), residual tumor size > 1.5 cm (OR = 0.278, p  = 0.043), and longer ISP (OR = 0.906, p  = 0.013)—particularly beyond 31 days (OR = 0.111, p  = 0.001)—as factors associated with a lower likelihood of CR. Multivariate analysis further confirmed that ISP was the only independent factor correlated with CR (OR = 0.884, p  = 0.009). Conclusion This study highlights that the timely initiation of PBT following surgery, particularly within 31 days, is associated with improved CR in pediatric medulloblastoma. Our findings suggest that a shorter interval between surgery and PBT initiation may be an important factor influencing early treatment response, providing preliminary evidence to support earlier postoperative PBT delivery.