Diffusion tensor imaging of deep gray matter in children treated for brain malignancies

Retrospective study of late radiation-induced damages after focal radiotherapy for childhood brain tumors

PURPOSE

To study a robust and reproducible procedure to investigate a relation between focal brain radiotherapy (RT) low doses, neurocognitive impairment and late White Matter and Gray Matter alterations, as shown by Diffusion Tensor Imaging (DTI), in children.

METHODS AND MATERIALS

Forty-five patients (23 males and 22 females, median age at RT 6.2 years, median age at evaluations 11.1 years) who had received focal RT for brain tumors were recruited for DTI exams and neurocognitive tests. Patients' brains were parceled in 116 regions of interest (ROIs) using an available segmented atlas. After the development of an ad hoc, home-made, multimodal and highly deformable registration framework, we collected mean RT doses and DTI metrics values for each ROI. The pattern of association between cognitive scores or domains and dose or DTI values was assessed in each ROI through both considering and excluding ROIs with mean doses higher than 75% of the prescription. Subsequently, a preliminary threshold value of dose discriminating patients with and without neurocognitive impairment was selected for the most relevant associations.

RESULTS

The workflow allowed us to identify 10 ROIs where RT dose and DTI metrics were significantly associated with cognitive tests results (p<0.05). In 5/10 ROIs, RT dose and cognitive tests were associated with p<0.01 and preliminary RT threshold dose values, implying a possible cognitive or neuropsychological damage, were calculated. The analysis of domains showed that the most involved one was the "school-related activities".

CONCLUSION

This analysis, despite being conducted on a retrospective cohort of children, shows that the identification of critical brain structures and respective radiation dose thresholds is achievable by combining, with appropriate methodological tools, the large amount of data arising from different sources. This supported the design of a prospective study to gain stronger evidence.

Quantitative Imaging Biomarkers of Damage to Critical Memory Regions Are Associated With Post-Radiation Therapy Memory Performance in Brain Tumor Patients

PURPOSE

We used quantitative magnetic resonance imaging to prospectively analyze the association between microstructural damage to memory-associated structures within the medial temporal lobe and longitudinal memory performance after brain radiation therapy (RT).

METHODS AND MATERIALS

Patients with a primary brain tumor receiving fractionated brain RT were enrolled on a prospective trial (n = 27). Patients underwent high-resolution volumetric brain magnetic resonance imaging, diffusion-weighted imaging, and neurocognitive testing before and 3, 6, and 12 months post-RT. Medial temporal lobe regions (hippocampus; entorhinal, parahippocampal, and temporal pole white matter [WM]) were autosegmented, quantifying volume and diffusion biomarkers of WM integrity (mean diffusivity [MD]; fractional anisotropy [FA]). Reliable change indices measured changes in verbal (Hopkins Verbal Learning Test-Revised) and visuospatial (Brief Visuospatial Memory Test-Revised [BVMT-R]) memory. Linear mixed-effects models assessed longitudinal associations between imaging parameters and memory.

RESULTS

Visuospatial memory significantly declined at 6 months post-RT (mean reliable change indices, -1.3; P = .012). Concurrent chemotherapy and seizures trended toward a significant association with greater decline in visuospatial memory (P = .053 and P = .054, respectively). Higher mean dose to the left temporal pole WM was significantly associated with decreased FA (r = -0.667; P = .002). Over all time points, smaller right hippocampal volume (P = .021), lower right entorhinal FA (P = .023), greater right entorhinal MD (P = .047), and greater temporal pole MD (BVMT-R total recall, P = .003; BVMT-R delayed recall, P = .042) were associated with worse visuospatial memory. The interaction between right entorhinal MD (BVMT-R total recall, P = .021; BVMT-R delayed recall, P = .004) and temporal pole FA (BVMT-R delayed recall, P = .024) significantly predicted visuospatial memory performance.

CONCLUSIONS

Brain tumor patients exhibited visuospatial memory decline post-RT. Microstructural damage to critical memory regions, including the hippocampus and medial temporal lobe WM, were associated with post-RT memory decline. The integrity of medial temporal lobe structures is critical to memory performance post-RT, representing possible avoidance targets for memory preservation.

Neurodevelopmental consequences of pediatric cancer and its treatment: applying an early adversity framework to understanding cognitive, behavioral, and emotional outcomes

Today, children are surviving pediatric cancer at unprecedented rates, making it one of modern medicine's true success stories. However, we are increasingly becoming aware of several deleterious effects of cancer and the subsequent "cure" that extend beyond physical sequelae. Indeed, survivors of childhood cancer commonly report cognitive, emotional, and psychological difficulties, including attentional difficulties, anxiety, and posttraumatic stress symptoms (PTSS). Cognitive late- and long-term effects have been largely attributed to neurotoxic effects of cancer treatments (e.g., chemotherapy, cranial irradiation, surgery) on brain development. The role of childhood adversity in pediatric cancer - namely, the presence of a life-threatening disease and endurance of invasive medical procedures - has been largely ignored in the existing neuroscientific literature, despite compelling research by our group and others showing that exposure to more commonly studied adverse childhood experiences (i.e., domestic and community violence, physical, sexual, and emotional abuse) strongly imprints on neural development. While these adverse childhood experiences are different in many ways from the experience of childhood cancer (e.g., context, nature, source), they do share a common element of exposure to threat (i.e., threat to life or physical integrity). Therefore, we argue that the double hit of early threat and cancer treatments likely alters neural development, and ultimately, cognitive, behavioral, and emotional outcomes. In this paper, we (1) review the existing neuroimaging research on child, adolescent, and adult survivors of childhood cancer, (2) summarize gaps in our current understanding, (3) propose a novel neurobiological framework that characterizes childhood cancer as a type of childhood adversity, particularly a form of early threat, focusing on development of the hippocampus and the salience and emotion network (SEN), and (4) outline future directions for research.

Longitudinal changes in gray matter regions after cranial radiation and comparative analysis with whole body radiation: a DTI study

PURPOSE

Radiation-induced white matter changes are well known and vastly studied. However, radiation-induced gray matter alterations are still a research question. In the present study, these changes were assessed in a longitudinal manner using Diffusion Tensor Imaging (DTI) and further compared for cranial and whole body radiation exposure.

MATERIALS AND METHODS

Male mice (C57BL/6) were irradiated with cranial or whole body radiation followed by DTI study at 7T animal MRI system during predose, subacute and early delayed phases of radiation sickness. Fractional anisotropy (FA) and mean diffusivity (MD) values were obtained from brain's gray matter regions.

RESULTS

Decreased FA with increased MD was observed prominently in animals exposed to cranial radiation showing most changes at 8 months post irradiation. However, whole body radiation induced FA changes were mostly observed at 1 month post irradiation as compared to controls.

CONCLUSIONS

The differential response after whole body and cranial irradiation observed in the study depicts that radiation exposure of 5 Gy could induce permanent alterations in gray matter regions prominently as observed in Caudoputamen region at all the time points. Thus, our study has bolstered the role of DTI to probe microstructural changes in gray matter regions of brain after radiation exposure.

Brain Perfusion and Diffusion Abnormalities in Children Treated for Posterior Fossa Brain Tumors

OBJECTIVE

To compare cerebral perfusion and diffusion in survivors of childhood posterior fossa brain tumor with neurologically normal controls and correlate differences with cognitive dysfunction.

STUDY DESIGN

We analyzed retrospectively arterial spin-labeled cerebral blood flow (CBF) and apparent diffusion coefficient (ADC) in 21 patients with medulloblastoma (MB), 18 patients with pilocytic astrocytoma (PA), and 64 neurologically normal children. We generated ANCOVA models to evaluate treatment effects on the cerebral cortex, thalamus, caudate, putamen, globus pallidus, hippocampus, amygdala, nucleus accumbens, and cerebral white matter at time points an average of 5.7 years after original diagnosis. A retrospective review of patient charts identified 12 patients with neurocognitive data and in whom the relationship between IQ and magnetic resonance imaging variables was assessed for each brain structure.

RESULTS

Patients with MB (all treated with surgery, chemotherapy, and radiation) had significantly lower global CBF relative to controls (10%-23% lower, varying by anatomic region, all adjusted P?<?.05), whereas patients with PA (all treated with surgery alone) had normal CBF. ADC was decreased specifically in the hippocampus and amygdala of patients with MB and within the amygdala of patients with PA but otherwise remained normal after therapy. In the patients with tumor previously evaluated for IQ, regional ADC, but not CBF, correlated with IQ (R²?=?0.33-0.75).

CONCLUSIONS

The treatment for MB, but not PA, was associated with globally reduced CBF. Treatment in both tumor types was associated with diffusion abnormalities of the mesial temporal lobe structures. Despite significant perfusion abnormalities in patients with MB, diffusion, but not perfusion, correlated with cognitive outcomes.

Magnetic resonance imaging based functional imaging in paediatric oncology

Imaging is central to management of solid tumours in children. Conventional magnetic resonance imaging (MRI) is the standard imaging modality for tumours of the central nervous system (CNS) and limbs and is increasingly used in the abdomen. It provides excellent structural detail, but imparts limited information about tumour type, aggressiveness, metastatic potential or early treatment response. MRI based functional imaging techniques, such as magnetic resonance spectroscopy, diffusion and perfusion weighted imaging, probe tissue properties to provide clinically important information about metabolites, structure and blood flow. This review describes the role of and evidence behind these functional imaging techniques in paediatric oncology and implications for integrating them into routine clinical practice.