The posterior cerebellum, a new organ at risk?

Abstract

Eekers et al. have recently proposed a neuro-oncology atlas, which was co-authored by most centers associated in the European Proton Therapy Network (EPTN; Figure 1). With the introduction of new treatment techniques, such as integrated magnetic resonance imaging and linear accelerators (MR-linac) or particle therapy, the prediction of clinical efficacy of these more costly treatment modalities becomes more relevant. One of the side-effects of brain irradiation, being cognitive decline, is one of the toxicities most difficult to measure and predict. In order to validly compare different treatment modalities, 1) a uniform nomenclature of the organs at risk (OARs), 2) uniform atlas-based delineation [e.g., Eekers et al.], 3) long-term follow-up data with standardized cognitive tests, 4) a large patient population, and 5) (thus derived) validated normal tissue complication probability (NTCP) models are mandatory. Apart from the Gondi model, in which the role of the dose to 40% of both hippocampi (HC) proves to be significantly related to cognition in 18 patients, no similar models are available. So there is a strong need for more NTCP models, on HC, brain tissue and possible other relevant brain structures. In this review we summarize the available evidence on the role of the posterior cerebellum as a possible new organ at risk for cognition, which is deemed relevant for irradiation of brain and head and neck tumors.

Keywords: Cognition; Delineation atlas; Neuro-oncology; Organ at risk; Posterior cerebellum; Radiotherapy.

Fig. 1

3D view of the Brain, brainstem, cerebellum posterior and anterior. Lateral view of a 3D-reconstruction on CT of: 1. Total brain (brown) and brainstem (red). 2. Brain (brown), brainstem (red), cerebellum posterior* (dark blue). 3. Right brain (brown), brainstem (red), right cerebellum anterior* (light blue) and right cerebellum posterior* (dark blue). *In accordance to Atlas for Neuro-Oncology (Eekers et al., submitted). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Role of cerebellum in cognition.