Relationships between Regional Radiation Doses and Cognitive Decline in Children Treated with Cranio-Spinal Irradiation for Posterior Fossa Tumors

The Role of TGF-β in Cognitive Decline Associated with Radiotherapy in Brain Tumor

Cognitive decline is a late adverse event in brain tumor survivors. The patients receiving radiation treatment exhibit a wide range of damage and impairment in attention, memory, and executive function compared to the untreated group. After radiation treatment, various changes are observed in astrocytes, oligodendrocytes, white matter, and vasculature. The major affected areas are the hippocampus and prefrontal cortex. Neurogenesis impairment is one of the primary mechanisms responsible for cognitive dysfunction. Various cytokines and growth factors are responsible for inducing apoptosis of neural cells, which results in impaired neurogenesis in response to radiotherapy. Transforming growth factor (TGF-β) is one of the key cytokines released in response to radiation. TGF-β plays a major role in neuronal apoptosis through various pathways such as the MAP kinase pathway, JAK/STAT pathway, and protein kinase pathway. In contrast, activation of the ALK5 pathway via TGF-β improves neurogenesis. So, the current review article focuses on the detailed effects of TGF-β on neuronal cells concerning radiation exposure. This in-depth knowledge will help researchers focus more on the TGF-β pathway and come up with new treatment schedules which will help reduce cognitive dysfunctions in brain tumor patients produced as a result of radiation therapy.

1-[(4-Nitrophenyl)sulfonyl]-4-phenylpiperazine treatment after brain irradiation preserves cognitive function in mice

BACKGROUND

Normal tissue toxicity is an inevitable consequence of primary or secondary brain tumor radiotherapy. Cranial irradiation commonly leads to neurocognitive deficits that manifest months or years after treatment. Mechanistically, radiation-induced loss of neural stem/progenitor cells, neuroinflammation, and demyelination are contributing factors that lead to progressive cognitive decline.

METHODS

The effects of 1-[(4-nitrophenyl)sulfonyl]-4-phenylpiperazine (NSPP) on irradiated murine neurospheres, microglia cells, and patient-derived gliomaspheres were assessed by sphere-formation assays, flow cytometry, and interleukin (IL)-6 enzyme-linked immunosorbent assay. Activation of the hedgehog pathway was studied by quantitative reverse transcription PCR. The in vivo effects of NSPP were analyzed using flow cytometry, sphere-formation assays, immunohistochemistry, behavioral testing, and an intracranial mouse model of glioblastoma.

RESULTS

We report that NSPP mitigates radiation-induced normal tissue toxicity in the brains of mice. NSPP treatment significantly increased the number of neural stem/progenitor cells after brain irradiation in female animals, and inhibited radiation-induced microglia activation and expression of the pro-inflammatory cytokine IL-6. Behavioral testing revealed that treatment with NSPP after radiotherapy was able to successfully mitigate radiation-induced decline in memory function of the brain. In mouse models of glioblastoma, NSPP showed no toxicity and did not interfere with the growth-delaying effects of radiation.

CONCLUSIONS

We conclude that NSPP has the potential to mitigate cognitive decline in patients undergoing partial or whole brain irradiation without promoting tumor growth and that the use of this compound as a radiation mitigator of radiation late effects on the central nervous system warrants further investigation.

Intellectual changes after radiation for children with brain tumors: which brain structures are most important?

BACKGROUND

The objective of this study was to evaluate the contribution of radiation dose to different intracranial structures on changes in intellectual function for children with brain tumors.

METHODS

We evaluated children with brain tumors treated in 2005-2017 who had longitudinal neuropsychological assessments and available photon dosimetric data (if radiation therapy [RT] given). Full Scale Intelligence Quotient (FSIQ) and index scores were evaluated (perceptual reasoning index [PRI], processing speed index [PSI], verbal comprehension index [VCI], and working memory index [WMI]). Multivariable linear mixed effects models were used to model endpoints, with age at RT and dose to different brain regions as fixed effects and patient-specific random intercepts. P-values (P*) were adjusted for multiple comparisons.

RESULTS

Sixty-nine patients were included, 56 of whom received RT. Median neuropsychological follow-up was 3.2 years. Right temporal lobe mean dose was strongly associated with decline in FSIQ (P* = 0.005); with each gray increase in mean dose, there was a decrease of 0.052 FSIQ points per year. Dose to 50% (D50) of the supratentorial brain was associated with decline in PSI (P* = 0.006) and WMI (P* = 0.001). Right and left hippocampus D50 were individually strongly associated with declines in VCI (P* = 0.009 for each). Presence of a ventriculoperitoneal shunt decreased FSIQ by 10 points.

CONCLUSIONS

We reported associations between dosimetry to specific brain regions and intellectual outcomes, with suggested avoidance structures during RT planning. These models can help clinicians anticipate changes in neurocognition post-RT and guide selection of an optimal RT plan.

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.

Variation in relative biological effectiveness for cognitive structures in proton therapy of pediatric brain tumors

BACKGROUND

Clinically, a constant value of 1.1 is used for the relative biological effectiveness (RBE) of protons, whereas in vitro the RBE has been shown to vary depending on physical dose, tissue type, and linear energy transfer (LET). As the LET increases at the distal end of the proton beam, concerns exist for an elevated RBE in normal tissues. The aim of this study was therefore to investigate the heterogeneity of RBE to brain structures associated with cognition (BSCs) in pediatric suprasellar tumors.

MATERIAL AND METHODS

Intensity-modulated proton therapy (IMPT) plans for 10 pediatric craniopharyngioma patients were re-calculated using 11 phenomenological and two plan-based variable RBE models. Based on LET, tissue dependence and number of data points used to fit the models, the three RBE models considered the most relevant for the studied endpoint were selected. Thirty BSCs were investigated in terms of RBE and dose/volume parameters.

RESULTS

For a representative patient, the median (range) dose-weighted mean RBE (RBE_d) across all BSCs from the plan-based models was among the lowest (1.09 (1.02-1.52) vs. the phenomenological models at 1.21 (0.78-2.24)). Omitting tissue dependency resulted in RBE_d at 1.21 (1.04-2.24). Across all patients, the narrower RBE model selection gave median RBE_d values from 1.22 to 1.30.

CONCLUSION

For all BSCs, there was a systematic model-dependent variation in RBE_d, mirroring the uncertainty in biological effects of protons. According to a refined selection of in vitro models, the RBE variation across BSCs was in effect underestimated when using a fixed RBE of 1.1.

Cerebellar-Subcortical-Cortical Systems as Modulators of Cognitive Functions

Over the past few decades, research has established that the cerebellum is involved in executive functions; however, its specific role remains unclear. There are numerous theories of cerebellar function and numerous cognitive processes falling under the umbrella of executive function, making investigations of the cerebellum's role in executive functioning challenging. In this review, we explored the role of the cerebellum in executive functioning through clinical and cognitive neuroscience frameworks. We reviewed the neuroanatomical systems and theoretical models of cerebellar functions and the multifaceted nature of executive functions. Using attention deficit hyperactivity disorder and cerebellar tumor as clinical developmental models of cerebellar dysfunction, and the functional magnetic resonance imaging literature, we reviewed evidence for cerebellar involvement in specific components of executive function in childhood, adolescence, and adulthood. There is evidence for posterior cerebellar contributions to working memory, planning, inhibition, and flexibility, but the heterogeneous literature that largely was not designed to study the cerebellum makes it difficult to determine specific functions of the cerebellum or cerebellar regions. In addition, while it is clear that cerebellar insult in childhood affects executive function performance later in life, more work is needed to elucidate the mechanisms by which executive dysfunction occurs and its developmental course. The limitations of the current literature are discussed and potential directions for future research are provided.

Regional Responses in Radiation-Induced Normal Tissue Damage

Normal tissue side effects remain a major concern in radiotherapy. The improved precision of radiation dose delivery of recent technological developments in radiotherapy has the potential to reduce the radiation dose to organ regions that contribute the most to the development of side effects. This review discusses the contribution of regional variation in radiation responses in several organs. In the brain, various regions were found to contribute to radiation-induced neurocognitive dysfunction. In the parotid gland, the region containing the major ducts was found to be critical in hyposalivation. The heart and lung were each found to exhibit regional responses while also mutually affecting each other's response to radiation. Sub-structures critical for the development of side effects were identified in the pancreas and bladder. The presence of these regional responses is based on a non-uniform distribution of target cells or sub-structures critical for organ function. These characteristics are common to most organs in the body and we therefore hypothesize that regional responses in radiation-induced normal tissue damage may be a shared occurrence. Further investigations will offer new opportunities to reduce normal tissue side effects of radiotherapy using modern and high-precision technologies.

Immune cell infiltration and cytokine secretion analysis reveal a non-inflammatory microenvironment of medulloblastoma

Medulloblastoma (MB) is the most common lethal malignant pediatric brain tumor. Adjuvant immunotherapy for medulloblastoma has been proposed in both pre-clinical and clinical practice. To provide a precision strategy of designing immunotherapy for MB, the present study performed a descriptive analysis of immune microenvironment in a cohort and compared the differences between four subgroups of MB. Subtypes (WNT, SHH Group 3 and Group 4) of medulloblastoma were identified using K-means clustering according to the expression of signature genes. Tumor infiltrating immune cell population was assessed by both bio-informative algorithm based on gene expression and immunohistochemistry staining. Cytokines in tumor microenvironment were detected using Luminex. Gene Set Enrichment Analysis demonstrated a raised immune response in the SHH subgroup. Lymphocyte infiltration was low in all four subgroups, while more CD4⁺ T cells were observed in the Group 4 subtype. Programmed cell death protein 1 (PD1)/ ligand 1 (PD-L1) expression was absent in the cohort. The SHH subtype recruited more activated tumor associated macrophage/microglia compared with the other subgroups. Cytokines within the MB microenvironment were low compared with the glioblastoma samples. In contrast to glioblastoma, the immune microenvironment of pediatric MB is non-inflammatory and does not recruit many immune cells. These observations provide important considerations for the design of immunotherapeutic approaches for MB, such as inducing more lymphocytes into the tumor microenvironment.

Neurocognitive impairment following proton therapy for paediatric brain tumour: a systematic review of post-therapy assessments

BACKGROUND

Proton therapy (PT), frequently utilised to treat paediatric brain tumour (PBT) patients, eliminates exit dose and minimises dose to healthy tissues that theoretically can mitigate treatment-related effects including cognitive deficits. As clinical outcome data are emerging, we aimed to systematically review current evidence of cognitive changes following PT of PBT.

MATERIALS AND METHODS

We searched PubMed and Scopus electronic databases to identify eligible reports on cognitive changes following PT of PBT according to PRISMA guidelines. Reports were extracted for information on demographics and cognitive outcomes. Then, they were systematically reviewed based on three themes: (1) comparison with photon therapy, (2) comparison with baseline cognitive measures, to population normative mean or radiotherapy-naïve PBT patients and (3) effects of dose distribution to cognition.

RESULTS

Thirteen reports (median size (range): 70 (12-144)) were included. Four reports compared the cognitive outcome between PBT patients treated with proton to photon therapy and nine compared with baseline/normative mean/radiotherapy naïve from which two reported the effects of dose distribution. Reports found significantly poorer cognitive outcome among patients treated with photon therapy compared with proton therapy especially in general cognition and working memory. Craniospinal irradiation (CSI) was consistently associated with poorer cognitive outcome while focal therapy was associated with minor cognitive change/difference. In limited reports available, higher doses to the hippocampus and temporal lobes were implicated to larger cognitive change.

CONCLUSION

Available evidence suggests that PT causes less cognitive deficits compared with photon therapy. Children who underwent focal therapy with proton were consistently shown to have low risk of cognitive deficit suggesting the need for future studies to separate them from CSI. Evidence on the effect of dose distribution to cognition in PT is yet to mature.

Improved neuropsychological outcomes following proton therapy relative to X-ray therapy for pediatric brain tumor patients

BACKGROUND

Survivors of pediatric brain tumors are at risk for impaired development in multiple neuropsychological domains. The purpose of this study was to compare neuropsychological outcomes of pediatric brain tumor patients who underwent X-ray radiotherapy (XRT) versus proton radiotherapy (PRT).

METHODS

Pediatric patients who underwent either XRT or PRT and received posttreatment age-appropriate neuropsychological evaluation-including measures of intelligence (IQ), attention, memory, visuographic skills, academic skills, and parent-reported adaptive functioning-were identified. Multivariate analyses were performed to assess differences in neuropsychological outcomes and included tests for interaction between treatment cohort and follow-up time.

RESULTS

Between 1998 and 2017, 125 patients with tumors located in the supratentorial (17.6%), midline (28.8%), or posterior fossa (53.6%) compartments received radiation and had posttreatment neuropsychological evaluation. Median age at treatment was 7.4 years. The PRT patient cohort had higher estimated SES and shorter median time from radiotherapy completion to last neuropsychological evaluation (6.7 vs 2.6 y, P < 0.001). On multivariable analysis, PRT was associated with higher full-scale IQ (β = 10.6, P = 0.048) and processing speed (β = 14.4, P = 0.007) relative to XRT, with trend toward higher verbal IQ (β = 9.9, P = 0.06) and general adaptive functioning (β = 11.4, P = 0.07). Planned sensitivity analyses truncating follow-up interval in the XRT cohort re-demonstrated higher verbal IQ (P = 0.01) and IQ (P = 0.04) following PRT, with trend toward improved processing speed (P = 0.09).

CONCLUSIONS

PRT is associated with favorable outcomes for intelligence and processing speed. Combined with other strategies for treatment de-intensification, PRT may further reduce neuropsychological morbidity of brain tumor treatment.

Neurodevelopmental effects of low dose ionizing radiation exposure: A systematic review of the epidemiological evidence

BACKGROUND

The neurodevelopmental effects of high doses of ionizing radiation (IR) in children are well established. To what extent such effects exist at low-to-moderate doses is unclear. Considering the increasing exposure of the general population to low-to-moderate levels of IR, predominantly from diagnostic procedures, the study of these effects has become a priority for radiation protection.

OBJECTIVES

We conducted a systematic review of the current evidence for possible effects of low-to-moderate IR doses received during gestation, childhood and adolescence on different domains of neurodevelopment.

DATA SOURCES

Searches were performed in PubMed, Scopus, EMBASE and Psychinfo on the 6th of June 2017 and repeated in December 2018.

STUDY ELIGIBILITY CRITERIA

We included studies evaluating the association between low-to-moderate IR doses received during gestation, childhood and adolescence, and neurodevelopmental functions.

STUDY APPRAISAL AND SYNTHESIS METHODS

Studies were evaluated using the Cochrane Collaboration's risk of bias tool adapted to environmental sciences. A qualitative synthesis was performed.

RESULTS

A total of 26 manuscripts were finally selected. Populations analyzed in these publications were exposed to the following sources of IR: atomic bomb (Hiroshima and Nagasaki), diagnostic/therapeutic radiation, and Chernobyl and nuclear weapon testing fallout. There was limited evidence for an association between low-to-moderate doses of IR and a decrease in general cognition and language abilities, that is, a causal interpretation is credible, but chance or confounding cannot not be ruled out with reasonable confidence. Evidence for a possible stronger effect when exposure occurred early in life, in particular, during the fetal period, was inadequate. Evidence for an association between IR and other specific domains, including attention, executive function, memory, processing speed, visual-spatial abilities, motor and socio-emotional development, was inadequate, due to the very limited number of studies found.

LIMITATIONS, CONCLUSIONS, AND IMPLICATIONS OF KEY FINDINGS

Overall, depending on the domain, there was limited to inadequate evidence for an effect of low-to-moderate IR doses on neurodevelopment. Heterogeneity across studies in terms of outcome and exposure assessment hampered any quantitative synthesis and any stronger conclusion. Future research with adequate dosimetry and covering a range of specific neurodevelopmental outcomes would likely contribute to improve the body of evidence.

SYSTEMATIC REVIEW REGISTRATION NUMBER

The systematic review protocol was registered in PROSPERO (registration number CRD42018091902).

Radiation doses to brain substructures associated with cognition in radiotherapy of pediatric brain tumors

Background: Several brain substructures associated with cognition (BSCs) are located close to typical pediatric brain tumors. Pediatric patients therefore have considerable risks of neurocognitive impairment after brain radiotherapy. In this study, we investigated the radiation doses received by BSCs for three common locations of pediatric brain tumor entities. Material and methods: For ten patients in each group [posterior fossa ependymoma (PFE), craniopharyngioma (CP), and hemispheric ependymoma (HE)], the cumulative fraction of BSCs volumes receiving various dose levels were analyzed. We subsequently explored the differences in dose pattern between the three groups and used available dose response models from the literature to estimate treatment-induced intelligence quotient (IQ) decline. Results: Doses to BSCs were found to differ considerably between the groups, depending on their position relative to the tumor. Large inter-patient variations were observed in the ipsilateral structures of the HE groups, and at low doses for all three groups. IQ decline estimates differed depending on the model applied, presenting larger variations in the HE group. Conclusion: While there were notable differences in the dose patterns between the groups, the extent of estimated IQ decline depended more on the model applied. This inter-model variability should be considered in dose-effect assessments on cognitive outcomes of pediatric patients.

Intelligence and posterior fossa tumors in Brazilian youth

Central nervous system tumors are the most frequent solid neoplasms in childhood and are frequently located in posterior fossa (PF). In Brazil, this diagnosis is associated to high mortality rates and this context is increasingly worrisome outside of large urban centers in which delayed diagnosis and defaulting from treatment compromise survivorship. Moreover, the lesion and therapeutic toxicity compromise cognitive domains. This study investigated the impact of PF tumors and their treatments on the intellectual capacity of 37 children and adolescents aged 6 to 16, divided into two groups: patients with low grade tumors, submitted only to neurosurgery (G1) and with tumors of higher malignancy submitted to neurosurgery, chemotherapy, and/or radiotherapy (G2). Using the Wechsler Intelligence Scales for Children, data reveal that G1 presented preserved mean performance, while G2 presented low average performance. Cluster-type analysis divided the participants into two groups regarding intelligence, clinical and sociodemographic variables. Inferential statistical analysis highlighted the influence of antineoplastic treatment on nonverbal domains. Mother's schooling demonstrated influence on verbal domains, revealing an important dissociation pattern. The results suggest the relevance of sociocultural factors on the expression of the damage, as well as the administration of radiotherapy at critical neurodevelopmental stages.

Long-term Survivors of Childhood Brain Tumors: Impact on General Health and Quality of Life

PURPOSE OF REVIEW

We review and summarize the key issues affecting general health and quality of life (QOL) of pediatric long-term survivors of brain tumors.

RECENT FINDINGS

Long-term survivors of brain tumors are at risk of considerable late morbidity and mortality. Lengthening survival in brain tumors has highlighted the deep impact of tumor and its treatment on the physical, psychological, functional, and social health and QOL of these survivors. Evolution in tumor therapy including surgery, radiotherapy, and systemic therapies, etc., has the potential to mitigate this impact to some extent. Sensitization of health staff, policy makers, and the primary designers of clinical trials towards integration of QOL end points while measuring survival in brain tumor patients is the need of the hour. New developments in tumor therapeutics must not only provide quantitative gain but also improve the quality of survival in these long-term survivors. While majority of the issues presented pertain to survivorship in pediatric brain tumor population, similar challenges are likely to exist in young adults surviving brain tumors as well.