Patterns of failure in pediatric medulloblastoma and implications for hippocampal sparing

Abstract

Background Hippocampal avoidance (HA) has been shown to preserve cognitive function in adult patients with cancer treated with whole‐brain radiation therapy for brain metastases. However, the feasibility of HA in pediatric patients with brain tumors has not been explored because of concerns of increased risk of relapse in the peri‐hippocampal region. Our aim was to determine patterns of recurrence and incidence of peri‐hippocampal relapse in pediatric patients with medulloblastoma (MB). Methods and materials We identified pediatric patients with MB treated with protons between 2002 and 2016 and who had recurrent disease. To estimate the risk of peri‐hippocampal recurrence, three hippocampal zones (HZs) were delineated corresponding to ≤5 mm (HZ‐1), 6 to 10 mm (HZ‐2), and >10 mm (HZ‐3) distance of the recurrence from the contoured hippocampi. To determine the feasibility of HA, three standard‐risk patients with MB were planned using either volumetric‐modulated arc therapy (VMAT) or intensity‐modulated proton therapy (IMPT) plans. Results Thirty‐eight patients developed a recurrence at a median of 1.6 years. Of the 25 patients who had magnetic resonance imaging of the recurrence, no patients failed within the hippocampus and only two patients failed within HZ‐1. The crude incidence of peri‐hippocampal failure was 8%. Both HA‐VMAT and HA‐IMPT plans were associated with significantly reduced mean dose to the hippocampi (p < .05). HA‐VMAT and HA‐IMPT plans were associated with decreased percentage of the third and lateral ventricles receiving the prescription craniospinal dose of 23.4 Gy. Conclusions Peri‐hippocampal failures are uncommon in pediatric patients with MB. Hippocampal avoidance should be evaluated in a prospective cohort of pediatric patients with MB. Plain Language Summary In this study, the patterns of disease recurrence in patients with a pediatric brain tumor known as medulloblastoma treated with proton radiotherapy were examined. The majority of failures occur outside of an important structure related to memory formation called the hippocampus. Hippocampal sparing radiation plans using proton radiotherapy were generated and showed that dose to the hippocampus was able to be significantly reduced. The study provides the rationale to explore hippocampal sparing in pediatric medulloblastoma in a prospective clinical trial.

Is the hippocampus‐sparing attempt really reasonable within the current technological possibilities?

“…We read with great interest the recently published article entitled "Patterns of failure in pediatric medulloblastoma and implications for hippocampal sparing" by Baliga et al 1 The study provides valuable insights into the patterns of failure in pediatric medulloblastoma, a common type of brain tumor that affects children. The authors also revealed that hippocampal-avoidance (HA) volumetric-modulated arc therapy and HA intensity-modulated proton therapy techniques to reduce dose to the hippocampus are dosimetrically feasible.…”

Proton PBS Planning Techniques, Robustness Evaluation, and OAR Sparing for the Whole-Brain Part of Craniospinal Axis Irradiation

“…Some toxicity types, for instance, those related to endocrine and neurocognitive functions, are unavoidable in the CSI phase of the treatment since the pituitary gland and brain are integral parts of the CTV. Consequently, sparing is only possible in the boost phase, although innovative ideas, such as hippocampal sparing CSI, have been investigated [ 1 , 2 , 3 ]. Due to its physical characteristics, the traditionally used megavoltage photon beam allows for only limited improvements in CSI-related toxicity reduction, even considering the high-technology advances in photon radiotherapy in recent decades [ 4 ].…”