Association between radiation dose to neuronal progenitor cell niches and temporal lobes and performance on neuropsychological testing in children: a prospective study

Pediatric CNS Radiation Oncology: Recent Developments and Novel Techniques

Radiation therapy (RT) is a cornerstone in the management of pediatric central nervous system (CNS) tumors. Recent advancements in RT delivery and techniques aim to enhance therapeutic effectiveness while minimizing both acute and long-term complications associated with pediatric brain RT. This paper highlights innovative developments in the field, including the clinical indications, benefits, and challenges of proton therapy and stereotactic radiotherapy. The ongoing refinement of risk-adapted RT volumes is highlighted, with examples of newly proposed germinoma RT volumes and hippocampal-sparing RT. Additionally, emerging experimental approaches, including FLASH therapy and theranostics, are also discussed as promising future directions. Further prospective, multi-institutional collaborative studies are essential to validate and expand upon the benefits outlined in this review.

Longitudinal analysis of cognitive function in patients treated with postoperative radiotherapy for grade 2 and 3 IDH mutant diffuse glioma

BACKGROUND

Postoperative radiotherapy and chemotherapy improve survival in IDH mutant diffuse glioma. We investigated whether neurocognitive function declines over time, and whether mean dose to the brain outside of CTV (mean brain dose) is related to neurocognitive function.

PATIENTS AND METHODS

Patients that underwent resection and postoperative radiotherapy for grade 2 or 3 IDH mutant diffuse glioma were tested using the Hopkins Verbal Learning Test, Letter Fluency and Trail Making Test before surgery and afterwards up until disease progression. Mixed effects models were fitted for each of three cognitive test scores, using time from surgery, mean brain dose, CTV volume, and tumor grade as fixed effects.

RESULTS

Between 1-10-2013 and 31-12-2022, 49 patients underwent longitudinal neurocognitive testing. Average mean dose to brain minus CTV was 17.8 Gy (95 % CI 16.1 - 19.4). At the time of analysis, median follow-up in patients free from disease progression was 5.8 years (range 1.1 - 20.8). Attrition rate during the first five years of follow up was 14.1 %. There was no decline of test performance over time (p ≥ 0.526). However, there was a negative effect of increasing mean brain dose on TMT score A (-0.11, p = 0.008) and TMT score B (-0.13, p = 0.004).

CONCLUSIONS

In this study, no effect of time after resection on test scores was found. Multivariable modelling indicates an negative relationship between mean brain dose and specific neurocognitive test scores, accounting for effects of tumor grade and CTV volume.

Pathological Mechanisms of Irradiation-Induced Neurological Deficits in the Developing Brain

Cranial irradiation or radiotherapy (CRT) is one of the essential therapeutic modalities for central nervous system (CNS) tumors, and its efficacy is well known. Nevertheless, CRT is also associated with brain damages such as focal cerebral necrosis, neuroinflammation, cerebral microvascular anomalies, neurocognitive dysfunction, and hormone deficiencies in children. Children's brains are much more sensitive to CRT compared to the adult's brains. Thus, children's brains are also more likely to develop long-term CRT complication, which severely lessens their long-term quality of life after treatment. CRT to the juvenile rat led to a retardation of growth of the cerebellum; both the gray and white matter and neurogenic regions like the subventricular zone and the dentate gyrus in the hippocampus were predominantly vulnerable to CRT. Also, CRT-induced cognitive changes typically manifested as deficits in hippocampal-related functions of learning as well as memory, such as spatial information processing. Fractionated CRT-stimulated cognitive decline and hormone deficiencies were precisely associated with augmented neuronal cell death, blockade of neurogenesis, and stimulation of astrocytes and microglia. Thus, the aim of this review is to highlight the pathological mechanism of CRT-induced neurological deficits in the developing brain.

Cognitive phenotypes: Unraveling the heterogeneity in cognitive dysfunction among patients with primary brain tumors receiving radiotherapy

BACKGROUND

Patients with primary brain tumors demonstrate heterogeneous patterns of cognitive dysfunction, which we explore using latent profile analysis to identify cognitive phenotypes and their trajectories in patients receiving radiotherapy (RT).

METHODS

Ninety-six patients completed neuropsychological testing before and post-RT (3, 6, and 12 months) on a prospective longitudinal trial, including measures of processing speed, executive function, language, and verbal and visual memory. Models with 2-4 classes were examined. Demographic and clinical data were examined across phenotypes and post-RT cognitive change was evaluated.

RESULTS

The optimal model identified 3 unique cognitive phenotypes including a group of patients with generalized impairments (11.5%), a group with isolated verbal memory impairments (21.9%), and a group with minimal impairments (66.7%). The Verbal Memory phenotype had fewer years of education (P = .007) and a greater proportion of males (P < .001); the Generalized group had a greater proportion of patients with IDH-wild type gliomas and showed greater symptoms of anxiety and poorer quality of life (P-values < .05); and the Minimal Impairment phenotype had higher rates of IDH-Mutant gliomas. Approximately 50% of patients declined on at least one cognitive domain with memory being the most vulnerable. Patients who declined reported greater symptoms of depression (P = .007) and poorer quality of life (P = .025).

CONCLUSIONS

We identified 3 distinct cognitive phenotypes in patients with primary brain tumors receiving RT, each associated with unique demographic and clinical (eg, IDH mutational status) profiles, with mood symptoms associated with late cognitive decline. This patient-centered approach enhances our understanding of clinical profiles associated with cognitive dysfunction and treatment-related neurotoxicity.

Dosimetric Evaluation of Hippocampus Sparing Intensity Modulated Radiation Therapy in Patients With Stage T1-T2 and Stage T3-T4 Nasopharyngeal Carcinoma

Purpose

To compare the hippocampus (HPC) dose reduced by HPC-sparing intensity modulated radiation therapy (IMRT) plans between nasopharyngeal carcinoma (NPC) patients of stages T1-T2 and T3-T4, and to investigate the correlation between the dose of the HPC and the volume of PTVnx70 (the planning target volume of the primary tumor in the nasopharynx that received 70 Gy).

Methods and Materials

Fifty-eight NPC patients were retrospectively evaluated. HPC-nonsparing IMRT or sparing IMRT for each patient was designed according to the protocol for NPC. Dose-volume histogram was used to evaluate the IMRT plans for each patient. The difference in values of HPC parameters (eg, Dmin[NS] - Dmin[S]) between HPC-sparing and nonsparing plans in the stage T1-T2 group and stage T3-T4 group were compared. The correlations between the dose of the HPC and the volume of PTVnx70 were analyzed.

Results

There was no significance between HPC-sparing and nonsparing IMRT plans. Compared with the HPC-nonsparing plans, the HPC-sparing plans significantly decreased both dosimetric and volumetric parameters for the HPC (P < .05), except for Dmin, D98%, and V5. The medians of Dmedian[NS] - Dmedian[S], Dmean[NS] - Dmean[S], D40%[NS] - D40%[S], V30[NS] - V30[S], V40[NS] - V40[S] and V50[NS] - V50[S] in the T1-T2 group were significantly lower than in the T3-T4 group (P < .05), respectively. Both dosimetric and volumetric parameters for the HPC were positively correlated with the volume of PTVnx70 in HPC-sparing and HPC-nonsparing plans (P < .05). The volume of PTVnx70 was positively correlated with Dmedian[NS] - Dmedian[S], Dmean[NS] - Dmean[S], D40%[NS] - D40%[S], V40[NS] - V40[S] and V50[NS] - V50[S] (P < .05).

Conclusions

HPC-sparing IMRT plans may play a more significant role in decreasing Dmedian, Dmean, D40%, and V30-V50 of HPC in NPC patients with stages T3-T4 than those in stages T1-T2. PTVnx70 volume of NPC patients is positively correlated with all dosimetric and volumetric parameters of HPC and the reduction of specific dosage parameters by HPC-sparing IMRT plans.

Cognitive dysfunction induced by cranial radiotherapy: mechanisms and therapeutic methods

Cranial radiotherapy can damage normal brain tissues, inducing cognitive dysfunction in patients. Radiotherapy-induced cognitive dysfunction is associated with hippocampal injury, white matter damage and microvascular injury. In this study, the mechanisms of cognitive dysfunction induced by cranial radiotherapy and combined chemoradiotherapy are reviewed, and the advances in therapeutic methods for radiotherapy-induced brain injury are summarized. The mechanisms of radiotherapy-induced brain injury include a decline of neurogenesis, impairment of neurons and glial cells, vascular injury, oxidative stress and DNA damage, cell death, and inflammatory response. Disruption of the bloodbrain barrier (BBB) increases the exposure of the brain to chemotherapeutic agents, thus exacerbating radiotherapy-induced brain damage. The current methods used to prevent radiotherapy-induced brain injury mainly include precision radiotherapy, stem cell transplantation, and treatment with neuroprotective drugs. The combined application of precision radiotherapy and neuroprotective drugs, including antioxidants, anti-inflammatory agents and other drugs, might exert better neuroprotective effects. To resolve the issues of neuroprotective drugs, such as difficulty in crossing the BBB, nanoenzymes and drug delivery nano-systems could be applied in the future.

Neurocognitive Effects and Necrosis in Childhood Cancer Survivors Treated With Radiation Therapy: A PENTEC Comprehensive Review

PURPOSE

A PENTEC review of childhood cancer survivors who received brain radiation therapy (RT) was performed to develop models that aid in developing dose constraints for RT-associated central nervous system (CNS) morbidities.

METHODS AND MATERIALS

A comprehensive literature search, through the PENTEC initiative, was performed to identify published data pertaining to 6 specific CNS toxicities in children treated with brain RT. Treatment and outcome data on survivors were extracted and used to generate normal tissue complication probability (NTCP) models.

RESULTS

The search identified investigations pertaining to 2 of the 6 predefined CNS outcomes: neurocognition and brain necrosis. For neurocognition, models for 2 post-RT outcomes were developed to (1) calculate the risk for a below-average intelligence quotient (IQ) (IQ <85) and (2) estimate the expected IQ value. The models suggest that there is a 5% risk of a subsequent IQ <85 when 10%, 20%, 50%, or 100% of the brain is irradiated to 35.7, 29.1, 22.2, or 18.1 Gy, respectively (all at 2 Gy/fraction and without methotrexate). Methotrexate (MTX) increased the risk for an IQ <85 similar to a generalized uniform brain dose of 5.9 Gy. The model for predicting expected IQ also includes the effect of dose, age, and MTX. Each of these factors has an independent, but probably cumulative effect on IQ. The necrosis model estimates a 5% risk of necrosis for children after 59.8 Gy or 63.6 Gy (2 Gy/fraction) to any part of the brain if delivered as primary RT or reirradiation, respectively.

CONCLUSIONS

This PENTEC comprehensive review establishes objective relationships between patient age, RT dose, RT volume, and MTX to subsequent risks of neurocognitive injury and necrosis. A lack of consistent RT data and outcome reporting in the published literature hindered investigation of the other predefined CNS morbidity endpoints.

Hippocampal region avoidance in whole brain radiotherapy in brain metastases: For all or for some? A real-world feasibility report

PURPOSE

Hippocampal sparing whole-brain radiotherapy (HS-WBRT) showed significantly lower long-term side effects compared to standard WBRT. Aim of this study is to describe a HS-WBRT real-world monoinstitutional experience within a retrospective cohort.

METHODS

Patients who completed HS-WBRT course, with Karnofsky Performance Status ⩾ 60 and radiological diagnosis of brain metastases (BMs) were enrolled. Treatment was performed using helical Tomotherapy scheduled in 30 Gy in 10 or 12 fractions or 25 Gy in 10 fractions. Oncological outcomes were clinically and radiologically assessed every three months. Toxicity was graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events 4.3.

RESULTS

One hundred and nineteen patients from 2016 to 2020 met inclusion criteria; after a median follow-up of 18 months, 29 patients were alive; 6- and 12-months overall survival rates were 66% and 41%, respectively. HS-WBRT response was assessed for 72 patients. Median time to any progression and intracranial failure (IF) was 4.5 and 13.7 months, respectively. The 6- and 12-month IF rates were 85% and 57%. Among 40 patients (34%) who experienced IF, 17 (42%) were oligometastatic, 23 (58%) polymetastatic and 15/40 developed IF within the hippocampi avoidance zone. No grade (G) ⩾ 2 acute toxicities were reported and one G2 (dizziness) late toxicity was described.

CONCLUSIONS

HS-WBRT is well tolerated, and despite the hippocampal sparing region, the oncological control is satisfying. Further investigation is warranted to find patients who could most benefit from a HS-WBRT approach.

Unilateral hippocampal sparing during whole brain radiotherapy for multiple brain metastases: narrative and critical review

Background

The landscape of brain metastases radiotherapy is evolving, with a shift away from whole-brain radiotherapy (WBRT) toward targeted stereotactic approaches aimed at preserving neurocognitive functions and maintaining overall quality of life. For patients with multiple metastases, especially in cases where targeted radiotherapy is no longer feasible due to widespread dissemination, the concept of hippocampal sparing radiotherapy (HA_WBRT) gains prominence.

Methods

In this narrative review we explore the role of the hippocampi in memory formation and the implications of their postradiotherapy lateral damage. We also consider the potential advantages of selectively sparing one hippocampus during whole-brain radiotherapy (WBRT). Additionally, by systematic evaluation of relevant papers published on PubMed database over last 20 years, we provide a comprehensive overview of the various changes that can occur in the left or right hippocampus as a consequence of radiotherapy.

Results

While it is important to note that various neurocognitive functions are interconnected throughout the brain, we can discern certain specialized roles of the hippocampi. The left hippocampus appears to play a predominant role in verbal memory, whereas the right hippocampus is associated more with visuospatial memory. Additionally, the anterior part of the hippocampus is more involved in episodic memory and emotional processing, while the posterior part is primarily responsible for spatial memory and pattern separation. Notably, a substantial body of evidence demonstrates a significant correlation between post-radiotherapy changes in the left hippocampus and subsequent cognitive decline in patients.

Conclusion

In the context of individualized palliative radiotherapy, sparing the unilateral (specifically, the left, which is dominant in most individuals) hippocampus could expand the repertoire of strategies available for adapted WBRT in cases involving multiple brain metastases where stereotactic radiotherapy is not a viable option. Prospective ongoing studies assessing various memory-sparing radiotherapy techniques will define new standard of radiotherapy care of patients with multiple brain metastases.

Bibliometric and visualization analysis of radiation brain injury from 2003 to 2023

Background

Over the past two decades, the field of radiation brain injury has attracted the attention of an increasing number of brain scientists, particularly in the areas of molecular pathology and therapeutic approaches. Characterizing global collaboration networks and mapping development trends over the past 20 years is essential.

Objective

The aim of this paper is to examine significant issues and future directions while shedding light on collaboration and research status in the field of radiation brain injury.

Methods

Bibliometric studies were performed using CiteSpaceR-bibliometrix and VOSviewer software on papers regarding radiation brain injury that were published before November 2023 in the Web of Science Core Collection.

Results

In the final analysis, we found 4,913 records written in 1,219 publications by 21,529 authors from 5,007 institutions in 75 countries. There was a noticeable increase in publications in 2014 and 2021. The majority of records listed were produced by China, the United States, and other high-income countries. The largest nodes in each cluster of the collaboration network were Sun Yat-sen University, University of California-San Francisco, and the University of Toronto. Galldiks N, Barnett GH, Langen KJ and Kim JH are known to be core authors in the field. The top 3 keywords in that time frame are radiation, radiation necrosis, and radiation-therapy.

Conclusions

The objective and thorough bibliometric analysis also identifies current research hotspots and potential future paths, providing a retrospective perspective on RBI and offering useful advice to researchers choosing research topics. Future development directions include the integration of multi-omics methodologies and novel imaging techniques to improve RBI's diagnostic effectiveness and the search for new therapeutic targets.

Comparison of Different Head Tilt Angles in Tomotherapy and Volumetric Modulated Arc Therapy for Hippocampal-Avoidance Whole-Brain Radiotherapy

PURPOSE

Hippocampal-avoidance whole-brain radiotherapy (HA-WBRT) planning can present challenges. This study examines the influence of head tilt angles on the dosimetric characteristics of target and organs at risk (OARs), aiming to identify the optimal tilt angle that yields optimal dosimetric outcomes using tomotherapy (TOMO).

METHODS

Eight patients diagnosed with brain metastases underwent CT scans at five tilt angles: [0°, 10°), [10°, 20°), [20°, 30°), [30°, 40°), and [40°, 45°]. Treatment plans were generated using TOMO and volumetric modulated arc therapy (VMAT). Dosimetric parameters including conformity index (CI), homogeneity index (HI), D2cc, D98%, and Dmean of PTV, as well as Dmax, and Dmean of OARs were analyzed. Furthermore, a comparison was made between the dosimetric parameters of TOMO and VMAT plans. Finally, delivery efficiency of TOMO plans were assessed.

RESULTS

For the PTV, [40°, 45°] tilt angle demonstrated significantly better conformity, homogeneity, lower D2cc, and lower Dmean for the PTV. Regarding the OARs, the [40°, 45°] head tilt angle demonstrated significantly lower Dmax and Dmean in hippocampus, eyes, optic chiasm, and optic nerves. The [40°, 45°] tilt angle also showed significantly lower Dmax for brainstem and cochleas, as well as a lower Dmean for lens. In the [40°,45°] tilt angle for HA-WBRT, TOMO showed superior performance over VMAT for the PTV. TOMO achieved lower Dmax for brainstem, cochleas, optic nerves, and optic chiasm, as well as a lower Dmean for hippocampus. Furthermore, a significant correlation was found between delivery time and the PTV projection length in the sagittal plane.

CONCLUSION

The TOMO plan utilizing a tilt angle range of [40°, 45°] demonstrated superior PTV conformity and uniformity, along with enhanced OARs sparing. Furthermore, it exhibited a dosimetric advantage over VMAT for PTV and most OARs at the same angle range.

Robustness and dosimetric verification of hippocampal-sparing craniospinal pencil beam scanning proton plans for pediatric medulloblastoma

Background and Purpose

Hippocampal-sparing (HS) is a method that can potentially reduce late cognitive complications for pediatric medulloblastoma (MB) patients treated with craniospinal proton therapy (PT). The aim of this study was to investigate robustness and dosimetric plan verification of pencil beam scanning HS PT.

Materials and Methods

HS and non-HS PT plans for the whole brain part of craniospinal treatment were created for 15 pediatric MB patients. A robust evaluation of the plans was performed. Plans were recalculated in a water phantom and measured field-by-field using an ion chamber detector at depths corresponding to the central part of hippocampi. All HS and non-HS fields were measured with the standard resolution of the detector and in addition 16 HS fields were measured with high resolution. Measured and planned dose distributions were compared using gamma evaluation.

Results

The median mean hippocampus dose was reduced from 22.9 Gy (RBE) to 8.9 Gy (RBE), while keeping CTV V95% above 95 % for all nominal HS plans. HS plans were relatively robust regarding hippocampus mean dose, however, less robust regarding target coverage and maximum dose compared to non-HS plans. For standard resolution measurements, median pass rates were 99.7 % for HS and 99.5 % for non-HS plans (p < 0.001). For high-resolution measurements, median pass rates were 100 % in the hippocampus region and 98.2 % in the surrounding region.

Conclusions

A substantial reduction of dose in the hippocampus region appeared feasible. Dosimetric accuracy of HS plans was comparable to non-HS plans and agreed well with planned dose distribution in the hippocampus region.

Cognition and Brain System Segregation in Pediatric Brain Tumor Patients Treated with Proton Therapy

Purpose

Pediatric brain tumor patients often experience significant cognitive sequelae. Resting-state functional MRI (rsfMRI) provides a measure of brain network organization, and we hypothesize that pediatric brain tumor patients treated with proton therapy will demonstrate abnormal brain network architecture related to cognitive outcome and radiation dosimetry.

Participants and Methods

Pediatric brain tumor patients treated with proton therapy were enrolled on a prospective study of cognitive assessment using the NIH Toolbox Cognitive Domain. rsfMRI was obtained in participants able to complete unsedated MRI. Brain system segregation (BSS), a measure of brain network architecture, was calculated for the whole brain, the high-level cognition association systems, and the sensory-motor systems.

Results

Twenty-six participants were enrolled in the study for cognitive assessment, and 18 completed rsfMRI. There were baseline cognitive deficits in attention and inhibition and processing speed prior to radiation with worsening performance over time in multiple domains. Average BSS across the whole brain was significantly decreased in participants compared with healthy controls (1.089 and 1.101, respectively; P = 0.001). Average segregation of association systems was significantly lower in participants than in controls (P < 0.001) while there was no difference in the sensory motor networks (P = 0.70). Right hippocampus dose was associated with worse attention and inhibition (P < 0.05) and decreased segregation in the dorsal attention network (P < 0.05).

Conclusion

Higher mean dose to the right hippocampus correlated with worse dorsal attention network segregation and worse attention and inhibition cognitive performance. Patients demonstrated alterations in brain network organization of association systems measured with rsfMRI; however, somatosensory system segregation was no different from healthy children. Further work with preradiation rsfMRI is needed to assess the effects of surgery and presence of a tumor on brain network architecture.

Patterns of failure in pediatric medulloblastoma and implications for hippocampal sparing

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.

Recent Updates on Radiation Therapy for Pediatric Optic Pathway Glioma

Optic pathway glioma (OPG) is a rare tumor located in optic nerve, optic tract, or optic chiasm. Treatment options for OPG include surgery, radiation therapy (RT), and chemotherapy. Although RT may provide favorable long-term outcomes in manner of either adjuvant or salvage aim, chemotherapy-first approach is increasingly performed due to possible late effects of RT. Proton beam RT may allow normal tissue sparing of radiation exposure compared to conventional X-ray treatment. Therefore, proton beam RT is expected to reduce complications from RT. This review discusses the recent updates on oncologic outcomes of OPG, late toxicities following RT, and compares the outcomes between X-ray treatment and proton beam RT.

Cross-translational models of late-onset cognitive sequelae and their treatment in pediatric brain tumor survivors

Pediatric brain tumor treatments have a high success rate, but survivors are at risk of cognitive sequelae that impact long-term quality of life. We summarize recent clinical and animal model research addressing pathogenesis or evaluating candidate interventions for treatment-induced cognitive sequelae. Assayed interventions encompass a broad range of approaches, including modifications to radiotherapy, modulation of immune response, prevention of treatment-induced cell loss or promotion of cell renewal, manipulation of neuronal signaling, and lifestyle/environmental adjustments. We further emphasize the potential of neuroimaging as a key component of cross-translation to contextualize laboratory research within broader clinical findings. This cross-translational approach has the potential to accelerate discovery to improve pediatric cancer survivors' long-term quality of life.

Irradiated microvascular endothelial cells may induce bystander effects in neural stem cells leading to neurogenesis inhibition

Radiation-induced neurocognitive dysfunction (RIND) has attracted a lot of attention lately due to the significant improvement of the survival of cancer patients after receiving cranial radiotherapy. The detailed mechanisms are not completely understood, but extensive evidence supports an involvement of the inhibition of hippocampal neurogenesis, which may result from radiation-induced depletion of neural stem cells (NSCs) as well as the damage to neurogenic niches. As an important component of neurogenic niches, vascular cells interact with NSCs through different signaling mechanisms, which is similar to the characteristics of radiation-induced bystander effect (RIBE). But whether RIBE is involved in neurogenesis inhibition contributed by the damaged vascular cells is unknown. Thus, the purpose of the present study was to investigate the occurrence of RIBEs in non-irradiated bystander NSCs induced by irradiated bEnd.3 vascular endothelial cells in a co-culture system. The results show that compared with the NSCs cultured alone, the properties of NSCs were significantly affected after co-culture with bEnd.3 cells, and further change was induced without obvious oxidative stress and apoptosis when bEnd.3 cells were irradiated, manifesting as a reduction in the proliferation, neurosphere-forming capability and differentiation potential of NSCs. All these results suggest that the damaged vascular endothelial cells may contribute to neurogenesis inhibition via inducing RIBEs in NSCs, thus leading to RIND.

Automatic Radiotherapy Planning for Glioblastoma Radiotherapy With Sparing of the Hippocampus and nTMS-Defined Motor Cortex

Background

Navigated transcranial magnetic stimulation (nTMS) of the motor cortex has been successfully implemented into radiotherapy planning by a number of studies. Furthermore, the hippocampus has been identified as a radiation-sensitive structure meriting particular sparing in radiotherapy. This study assesses the joint protection of these two eloquent brain regions for the treatment of glioblastoma (GBM), with particular emphasis on the use of automatic planning.

Patients and Methods

Patients with motor-eloquent brain glioblastoma who underwent surgical resection after nTMS mapping of the motor cortex and adjuvant radiotherapy were retrospectively evaluated. The radiotherapy treatment plans were retrieved, and the nTMS-defined motor cortex and hippocampus contours were added. Four additional treatment plans were created for each patient: two manual plans aimed to reduce the dose to the motor cortex and hippocampus by manual inverse planning. The second pair of re-optimized plans was created by the Auto-Planning algorithm. The optimized plans were compared with the “Original” plan regarding plan quality, planning target volume (PTV) coverage, and sparing of organs at risk (OAR).

Results

A total of 50 plans were analyzed. All plans were clinically acceptable with no differences in the PTV coverage and plan quality metrics. The OARs were preserved in all plans; however, overall the sparing was significantly improved by Auto-Planning. Motor cortex protection was feasible and significant, amounting to a reduction in the mean dose by &gt;6 Gy. The dose to the motor cortex outside the PTV was reduced by &gt;12 Gy (mean dose) and &gt;5 Gy (maximum dose). The hippocampi were significantly improved (reduction in mean dose: ipsilateral &gt;6 Gy, contralateral &gt;4.6 Gy; reduction in maximum dose: ipsilateral &gt;5 Gy, contralateral &gt;5 Gy). While the dose reduction using Auto-Planning was generally better than by manual optimization, the radiated total monitor units were significantly increased.

Conclusion

Considerable dose sparing of the nTMS-motor cortex and hippocampus could be achieved with no disadvantages in plan quality. Auto-Planning could further contribute to better protection of OAR. Whether the improved dosimetric protection of functional areas can translate into improved quality of life and motor or cognitive performance of the patients can only be decided by future studies.

Associations between patient-reported outcomes and radiation dose in patients treated with radiation therapy for primary brain tumours

AIM

This study aimed to explore associations between radiation dose and patient-reported outcomes in patients with a primary non-glioblastoma brain tumour treated with radiation therapy (RT), with a focus on health-related quality-of-life (HRQoL) and self-reported cognitive function.

METHODS

In this cross-sectional study, 78 patients who had received RT for a non-glioblastoma primary brain tumour, underwent neuropsychological testing and completed questionnaires on HRQoL, cognitive function, fatigue, depression, anxiety and perceived stress. The study explores the association between HRQoL scores, self-reported cognitive function and radiation doses to total brain, brainstem, hippocampus, thalamus, temporal lobes and frontal lobes. In addition, we examined correlations between neuropsychological test scores and self-reported cognitive function.

RESULTS

The median time between RT and testing was 4.6 years (range 1-9 years). Patients who had received high mean radiation doses to the total brain had low HRQoL scores (Cohen's d = 0.50, p = 0.04), brainstem (d = 0.65, p = 0.01) and hippocampus (d = 0.66, p = 0.01). High mean doses to the total brain were also associated with low scores on self-reported cognitive functioning (Cohen's d = 0.64, p = 0.02), brainstem (d = 0.55, p = 0.03), hippocampus (d = 0.76, p < 0.01), temporal lobes (d = 0.70, p < 0.01) and thalamus (d = 0.64, p = 0.01). Self-reported cognitive function correlated well with neuropsychological test scores (correlation range 0.27-0.54.).

CONCLUSIONS

High radiation doses to specific brain structures may be associated with impaired HRQoL and self-reported cognitive function with potentially negative implications to patients' daily lives. Patient-reported outcomes of treatment-related side-effects and their associations with radiation doses to the brain and its sub-structures may provide important information on radiation tolerance to the brain and sub-structures.

Partial-Brain Radiation-Induced Microvascular Cognitive Impairment in Juvenile Murine Unilateral Hippocampal Synaptic Plasticity

PURPOSE

Radiation-induced cognitive deficits have a severe negative impact on pediatric brain tumor patients. The severity of cognitive symptoms is related to the age of the child when radiation was applied, with the most severe effects seen in the youngest. Previous studies using whole-brain irradiation in mice confirmed these findings. To understand ipsilateral and contralateral changes in the hippocampus after partial-brain radiation therapy (PBRT) of the left hemisphere, we assessed the neuroplasticity and changes in the microvasculature of the irradiated and nonirradiated hippocampus in juvenile mice.

METHODS AND MATERIALS

The left hemispheres of 5-week-old mice were irradiated with 2, 8, and 20 Gy and a fractionated dose of 8 Gy in 2 fractions using a computed tomography image guided small animal radiation research platform. Long-term potentiation (LTP) has been monitored ex vivo in the hippocampal cornu ammonis 1 (CA1) region and was assessed 3 days and 5 and 10 weeks after PBRT in both hemispheres and compared to a sham group. Irradiation effects on the hippocampus microvasculature were quantified by efficient tissue clearing and multiorgan volumetric imaging.

RESULTS

LTP in irradiated hippocampal slices of juvenile mice declines 3 days after radiation, lasts up to 10 weeks in the irradiated part of the hippocampus, and correlates with a significantly reduced microvasculature length. Specifically, LTP inhibition is sustained in the irradiated (20 Gy, 8 Gy in 2 fractions, 8 Gy, 2 Gy) hippocampus, whereas the contralateral hippocampus remains unaffected after PBRT. LTP inhibition in the irradiated hemisphere after PBRT might be associated with an impaired microvascular network.

CONCLUSION

PBRT induces a long-lasting impairment in neuroplasticity and the microvessel network of the irradiated hippocampus, whereas the contralateral hippocampus remains unaffected. These findings provide insight into the design of PBRT strategies to better protect the young developing brain from cognitive decline.

The Advantage of Proton Therapy in Hypothalamic-Pituitary Axis and Hippocampus Avoidance for Children with Medulloblastoma

Purpose

Craniospinal irradiation (CSI) improves clinical outcomes at the cost of long-term neuroendocrine and cognitive sequelae. The purpose of this pilot study was to determine whether hypothalamic-pituitary axis (HPA) and hippocampus avoidance (HPA-HA) with intensity-modulated proton therapy (IMPT) can potentially reduce this morbidity compared with standard x-ray CSI.

Materials and Methods

We retrospectively evaluated 10 patients with medulloblastoma (mean, 7 years; range, 4-14 years). Target volumes and organs at risk were delineated as per our local protocol and the ACNS0331 atlas. An experienced neuroradiologist verified the HPA and hippocampus contours. The primary objective was CSI and boost clinical target volume (CTV) covering 95% of the volume (D₉₅) > 99% coverage with robustness. Described proton therapy doses in grays are prescribed using a biological effectiveness relative to photon therapy of 1.1. The combined prescribed dose in the boost target was 54 Gy. Secondary objectives included the HPA and hippocampus composite average dose (D_mean ≤ 18 Gy). For each patient, volumetric modulated arc radiotherapy (VMAT) and tomotherapy (TOMO) plans existed previously, and a new plan was generated with 3 cranial and 1 or 2 spinal beams for pencil-beam scanning delivery. Statistical comparison was performed with 1-way analysis of variance.

Results

Compared with standard CSI, HPA-HA CSI had statistically significant decreases in the composite doses received by the HPA (32.2 versus 17.9 Gy; P < .001) and hippocampi (39.8 versus 22.8 Gy; P < .001). The composite HPA D_mean was lower in IMPT plans (17.9 Gy) compared with that of VMAT (21.8 Gy) and TOMO (21.2 Gy) plans (P = .05). Hippocampi composite D_mean was also lower in IMPT plans (21 Gy) compared with that of VMAT (27.5 Gy) and TOMO (27.2 Gy) plans (P = .02). The IMPT CTV D₉₅ coverage was lower in IMPT plans (52.8 Gy) compared with that of VMAT (54.6 Gy) and TOMO (54.6 Gy) plans (P < .001) The spared mean volume was only 1.35% (19.8 cm³) of the whole-brain CTV volume (1476 cm³).

Conclusion

We found that IMPT has the strong potential to reduce the dose to the HPA and hippocampus, compared with standard x-ray CSI while maintaining target coverage. A prospective clinical trial is required to establish the safety, efficacy, and toxicity of this novel CSI approach.

Metformin pretreatment rescues olfactory memory associated with subependymal zone neurogenesis in a juvenile model of cranial irradiation

Cranial irradiation (IR) is an effective adjuvant therapy in the treatment of childhood brain tumors but results in long-lasting cognitive deficits associated with impaired neurogenesis, as evidenced in rodent models. Metformin has been shown to expand the endogenous neural stem cell (NSC) pool and promote neurogenesis under physiological conditions and in response to neonatal brain injury, suggesting a potential role in neurorepair. Here, we assess whether metformin pretreatment, a clinically feasible treatment for children receiving cranial IR, promotes neurorepair in a mouse cranial IR model. Using immunofluorescence and the in vitro neurosphere assay, we show that NSCs are depleted by cranial IR but spontaneously recover, although deficits to proliferative neuroblasts persist. Metformin pretreatment enhances the recovery of neurogenesis, attenuates the microglial response, and promotes recovery of long-term olfactory memory. These findings indicate that metformin is a promising candidate for further preclinical and clinical investigations of neurorepair in childhood brain injuries.

Out-of-Field Hippocampus from Partial-Body Irradiated Mice Displays Changes in Multi-Omics Profile and Defects in Neurogenesis

The brain undergoes ionizing radiation exposure in many clinical situations, particularly during radiotherapy for brain tumors. The critical role of the hippocampus in the pathogenesis of radiation-induced neurocognitive dysfunction is well recognized. The goal of this study is to test the potential contribution of non-targeted effects in the detrimental response of the hippocampus to irradiation and to elucidate the mechanisms involved. C57Bl/6 mice were whole body (WBI) or partial body (PBI) irradiated with 0.1 or 2.0 Gy of X-rays or sham irradiated. PBI consisted of the exposure of the lower third of the mouse body, whilst the upper two thirds were shielded. Hippocampi were collected 15 days or 6 months post-irradiation and a multi-omics approach was adopted to assess the molecular changes in non-coding RNAs, proteins and metabolic levels, as well as histological changes in the rate of hippocampal neurogenesis. Notably, at 2.0 Gy the pattern of early molecular and histopathological changes induced in the hippocampus at 15 days following PBI were similar in quality and quantity to the effects induced by WBI, thus providing a proof of principle of the existence of out-of-target radiation response in the hippocampus of conventional mice. We detected major alterations in DAG/IP3 and TGF-β signaling pathways as well as in the expression of proteins involved in the regulation of long-term neuronal synaptic plasticity and synapse organization, coupled with defects in neural stem cells self-renewal in the hippocampal dentate gyrus. However, compared to the persistence of the WBI effects, most of the PBI effects were only transient and tended to decrease at 6 months post-irradiation, indicating important mechanistic difference. On the contrary, at low dose we identified a progressive accumulation of molecular defects that tended to manifest at later post-irradiation times. These data, indicating that both targeted and non-targeted radiation effects might contribute to the pathogenesis of hippocampal radiation-damage, have general implications for human health.

Targeted Dorsal Dentate Gyrus or Whole Brain Irradiation in Juvenile Mice Differently Affects Spatial Memory and Adult Hippocampal Neurogenesis

The cognitive consequences of postnatal brain exposure to ionizing radiation (IR) at low to moderate doses in the adult are not fully established. Because of the advent of pediatric computed tomography scans used for head exploration, improving our knowledge of these effects represents a major scientific challenge. To evaluate how IR may affect the developing brain, models of either whole brain (WB) or targeted dorsal dentate gyrus (DDG) irradiation in C57Bl/6J ten-day-old male mice were previously developed. Here, using these models, we assessed and compared the effect of IR (doses range: 0.25-2 Gy) on long-term spatial memory in adulthood using a spatial water maze task. We then evaluated the effects of IR exposure on adult hippocampal neurogenesis, a form of plasticity involved in spatial memory. Three months after WB exposure, none of the doses resulted in spatial memory impairment. In contrast, a deficit in memory retrieval was identified after DDG exposure for the dose of 1 Gy only, highlighting a non-monotonic dose-effect relationship in this model. At this dose, a brain irradiated volume effect was also observed when studying adult hippocampal neurogenesis in the two models. In particular, only DDG exposure caused alteration in cell differentiation. The most deleterious effect observed in adult hippocampal neurogenesis after targeted DDG exposure at 1 Gy may contribute to the memory retrieval deficit in this model. Altogether these results highlight the complexity of IR mechanisms in the brain that can lead or not to cognitive disorders and provide new knowledge of interest for the radiation protection of children.

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.

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.

Radiation-induced bystander effects may contribute to radiation-induced cognitive impairment

PURPOSE

Despite being a major treatment modality for brain cancer due to its efficiency in achieving cancer control, radiotherapy has long been known to cause long-term side effects, including radiation-induced cognitive impairment (RICI). Neurogenesis inhibition due to radiation-induced damage in neural stem cells (NSCs) has been demonstrated to be an important mechanism underlying RICI. Radiation-induced bystander effects (RIBEs) denote the biological responses in non-targeted cells after their neighboring cells are irradiated. We have previously demonstrated that RIBEs could play an important role in the skin wound healing process. Therefore, we aimed to investigate whether RIBEs contribute to RICI in this study.

MATERIALS AND METHODS

The transwell co-culture method was used to investigate bystander effects in mouse NSCs induced by irradiated GL261 mouse glioma cells in vitro. The proliferation, neurosphere-forming capacity and differentiation potential of NSCs were determined as the bystander endpoints. The exosomes were extracted from the media used to culture GL261 cells and were injected into the hippocampus of C57BL/6 mice. Two months later, the neurogenesis of mice was assessed using BrdU incorporation and immunofluorescence microscopy, and cognitive function was evaluated by the Morris Water Maze.

RESULTS

After co-culture with GL261 glioma cells, mouse NSCs displayed inhibited proliferation and reduced neurosphere-forming capacity and differentiation potential. The irradiated GL261 cells caused greater inhibition and reduction in NSCs than unirradiated GL261 cells. Moreover, adding the exosomes secreted by GL261 cells into the culture of NSCs inhibited NSC proliferation, suggesting that the cancer cell-derived exosomes may be critical intercellular signals. Furthermore, injection of the exosomes from GL261 cells into the hippocampus of mice caused significant neurogenesis inhibition and cognitive impairment two month later, and the exosomes from irradiated GL261 cells induced greater inhibitory effects.

CONCLUSION

RIBEs mediated by the exosomes from irradiated cancer cells could contribute to RICI and, therefore, could be a novel mechanism underlying RICI.

A Prospective Cohort Study of Neural Progenitor Cell-Sparing Radiation Therapy Plus Temozolomide for Newly Diagnosed Patients With Glioblastoma

BACKGROUND

In treating glioblastoma, irradiation of the neural progenitor cell (NPC) niches is controversial. Lower hippocampal doses may limit neurocognitive toxicity, but higher doses to the subventricular zones (SVZ) may improve survival.

OBJECTIVE

To prospectively evaluate the impact of limiting radiation dose to the NPC niches on tumor progression, survival, and cognition in patients with glioblastoma.

METHODS

Patients with glioblastoma received resection followed by standard chemoradiation. Radiation dose to the NPC niches, including the bilateral hippocampi and SVZ, was minimized without compromising tumor coverage. The primary outcome was tumor progression in the spared NPC niches. Follow-up magnetic resonance imaging was obtained bimonthly. Neurocognitive testing was performed before treatment and at 6- and 12-mo follow-up. Cox regression evaluated predictors of overall and progression-free survival. Linear regression evaluated predictors of neurocognitive decline.

RESULTS

A total of 30 patients enrolled prospectively. The median age was 58 yr. Median mean doses to the hippocampi and SVZ were 49.1 and 41.8 gray (Gy) ipsilaterally, and 16.5 and 19.9 Gy contralaterally. Median times to death and tumor progression were 16.0 and 7.6 mo, and were not significantly different compared to a matched historical control. No patients experienced tumor progression in the spared NPC-containing regions. Overall survival was associated with neurocognitive function (P ≤ .03) but not dose to the NPC niches. Higher doses to the hippocampi and SVZ predicted greater decline in verbal memory (P ≤ .01).

CONCLUSION

In treating glioblastoma, limiting dose to the NPC niches may reduce cognitive toxicity while maintaining clinical outcomes. Further studies are needed to confirm these results.

Radiation-induced astrocyte senescence is rescued by Δ133p53

BACKGROUND

Cellular senescence and the senescence-associated secretory phenotype (SASP) may contribute to the development of radiation therapy-associated side effects in the lung and blood vessels by promoting chronic inflammation. In the brain, inflammation contributes to the development of neurologic disease, including Alzheimer's disease. In this study, we investigated the roles of cellular senescence and Δ133p53, an inhibitory isoform of p53, in radiation-induced brain injury.

METHODS

Senescent cell types in irradiated human brain were identified with immunohistochemical labeling of senescence-associated proteins p16INK4A and heterochromatin protein Hp1γ in 13 patient cases, including 7 irradiated samples. To investigate the impact of radiation on astrocytes specifically, primary human astrocytes were irradiated and examined for expression of Δ133p53 and induction of SASP. Lentiviral expression of ∆133p53 was performed to investigate its role in regulating radiation-induced cellular senescence and astrocyte-mediated neuroinflammation.

RESULTS

Astrocytes expressing p16INK4A and Hp1γ were identified in all irradiated tissues, were increased in number in irradiated compared with untreated cancer patient tissues, and had higher labeling intensity in irradiated tissues compared with age-matched controls. Human astrocytes irradiated in vitro also experience induction of cellular senescence, have diminished Δ133p53, and adopt a neurotoxic phenotype as demonstrated by increased senescence-associated beta-galactosidase activity, p16INK4A, and interleukin (IL)-6. In human astrocytes, Δ133p53 inhibits radiation-induced senescence, promotes DNA double-strand break repair, and prevents astrocyte-mediated neuroinflammation and neurotoxicity.

CONCLUSIONS

Restoring expression of the endogenous p53 isoform, ∆133p53, protects astrocytes from radiation-induced senescence, promotes DNA repair, and inhibits astrocyte-mediated neuroinflammation.

Early volume reduction of the hippocampus after whole-brain radiation therapy: an automated brain structure segmentation study

PURPOSE

To assess atrophy differences among brain regions and time-dependent changes after whole-brain radiation therapy (WBRT).

MATERIALS AND METHODS

Twenty patients with lung cancer who underwent both WBRT and chemotherapy (WBRT group) and 18 patients with lung cancer who underwent only chemotherapy (control group) were recruited. Three-dimensional T1WI were analyzed to calculate volume reduction ratio after WBRT in various brain structures. The volume reduction ratio of the hippocampus was compared among following 3 periods: 0-3, 4-7, and 8-11 months after WBRT.

RESULTS

The volume reduction ratio of the hippocampus was significantly higher in the WBRT group than in the control group (p < 0.05). In WBRT group, the volume reduction ratio of the hippocampus was significantly higher than that of the cortex and white matter (p < 0.05). There were significant differences in the volume reduction ratio between of 0-3 months and that of 4-7 months (p = 0.02) and between 4-7 months and that of 8-11 months (p = 0.01).

CONCLUSION

The hippocampus is more vulnerable to the radiation compared with other brain regions and may become atrophic even in the early stage after WBRT.

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.

Therapeutic strategy for pineal parenchymal tumor of intermediate differentiation (PPTID): case report of PPTID with malignant transformation to pineocytoma with leptomeningeal dissemination 6 years after surgery

Pineal parenchymal tumor of intermediate differentiation (PPTID) is rare. The WHO first classified PPTID in 2000 as a pineal parenchymal tumor (PPT) with an intermediate prognosis between pineocytoma (PC) and pineoblastoma (PB). It is considered an intermediate-grade tumor and divided into WHO grade II or III.The number of available reports about PPTID is presently limited, and the appropriate management for this tumor has not yet been determined.The authors report a rare case of PC in a 63-year-old woman who presented with lower-extremity weakness and gait disturbance. A pineal mass lesion was detected on MRI. A diagnosis of PC was established after microsurgical gross-total tumor resection, and the patient received no adjuvant therapy after surgery. Two years after surgery, a partial recurrence was recognized and Gamma Knife radiosurgery was performed. Fours years later, the patient developed diffuse leptomeningeal dissemination. She was successfully treated with craniospinal irradiation. Leptomeningeal dissemination may develop 6 years after the initial diagnosis of PC. A histopathological study of the recurrent tumor revealed a malignant change from PC to PPTID.The present case shows the importance of long-term follow-up of patients with PPTs following resection and the efficacy of craniospinal irradiation in the treatment of leptomeningeal dissemination.

Whole-ventricular irradiation for intracranial germ cell tumors: Dosimetric comparison of pencil beam scanned protons, intensity-modulated radiotherapy and volumetric-modulated arc therapy

Background

Whole-ventricular radiotherapy (WV-RT) followed by a boost to the tumor bed (WV-RT/TB) is recommended for intracranial germ cell tumors (IGCT). As the critical brain areas are mainly in the target volume vicinity, it is unclear if protons indeed substantially spare neurofunctional organs at risk (NOAR). Therefore, a dosimetric comparison study of WV-RT/TB was conducted to assess whether proton or photon radiotherapy achieves better NOAR sparing.

Methods

Eleven children with GCT received 24 Gy(RBE) WV-RT and a boost up to 40 Gy(RBE) in 25 fractions of 1.6 Gy(RBE) with pencil beam scanning proton therapy (PBS-PT). Intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans were generated for these patients. NOAR were delineated and treatment plans were compared for target volume coverage (TVC), homogeneity index (HI), inhomogeneity coefficient (IC) and (N)OAR sparing.

Results

TVC was comparable for all three modalities. Compared to IMRT and VMAT, PBS-PT showed statistically significant optimized IC, as well as dose reduction, among others, in mean and integral dose to the: normal brain (-35.2%, -32.7%; -35.2%, -33.0%, respectively), cerebellum (-53.7%, -33.1%; -53.6%, -32.7%) and right temporal lobe (-14.5%, -31.9%; -14.7%, -29.9%). The Willis' circle was better protected with PBS-PT than IMRT (-7.1%; -7.8%). The left hippocampus sparing was higher with IMRT. Compared to VMAT, the dose to the hippocampi, amygdalae and temporal lobes was significantly decreased in the IMRT plans.

Conclusions

Dosimetric comparison of WV-RT/TB in IGCT suggests PBS-PT's advantage over photons in conformality and NOAR sparing, whereas IMRT's superiority over VMAT, thus potentially minimizing long-term sequelae.

Dosimetric Comparison of Proton Radiation Therapy, Volumetric Modulated Arc Therapy, and Three-Dimensional Conformal Radiotherapy Based on Intracranial Tumor Location

(1) Background: Selecting patients that will benefit the most from proton radiotherapy (PRT) is of major importance. This study sought to assess dose reductions to numerous organs-at-risk (OARs) with PRT, as compared to three-dimensional conformal radiotherapy (3DCRT) and volumetric-modulated arc therapy (VMAT), as a function of tumor location. (2) Materials/Methods: Patients with intracranial neoplasms (all treated with PRT) were stratified into five location-based groups (frontal, suprasellar, temporal, parietal, posterior cranial fossa; n = 10 per group). Each patient was re-planned for 3DCRT and intensity-modulated radiotherapy (IMRT) using similar methodology, including the originally planned target and organ-at-risk (OAR) dose constraints. (3) Results: In parietal tumors, PRT showed the most pronounced dose reductions. PRT lowered doses to nearly every OAR, most notably the optical system and several contralateral structures (subventricular zone, thalamus, hippocampus). For frontal lobe cases, the greatest relative dose reductions in mean dose (D_mean) with PRT were to the infratentorial normal brain, contralateral hippocampus, brainstem, pituitary gland and contralateral optic nerve. For suprasellar lesions, PRT afforded the greatest relative D_mean reductions to the infratentorial brain, supratentorial brain, and the whole brain. Similar results could be observed in temporal and posterior cranial fossa disease. (4) Conclusions: The effectiveness and degree of PRT dose-sparing to various OARs depends on intracranial tumor location. These data will help to refine selection of patients receiving PRT, cost-effectiveness, and future clinical toxicity assessment.

Grafting Neural Stem and Progenitor Cells Into the Hippocampus of Juvenile, Irradiated Mice Normalizes Behavior Deficits

The pool of neural stem and progenitor cells (NSPCs) in the dentate gyrus of the hippocampus is reduced by ionizing radiation. This explains, at least partly, the learning deficits observed in patients after radiotherapy, particularly in pediatric cases. An 8 Gy single irradiation dose was delivered to the whole brains of postnatal day 9 (P9) C57BL/6 mice, and BrdU-labeled, syngeneic NSPCs (1.0 × 10⁵ cells/injection) were grafted into each hippocampus on P21. Three months later, behavior tests were performed. Irradiation impaired novelty-induced exploration, place learning, reversal learning, and sugar preference, and it altered the movement pattern. Grafting of NSPCs ameliorated or even normalized the observed deficits. Less than 4% of grafted cells survived and were found in the dentate gyrus 5 months later. The irradiation-induced loss of endogenous, undifferentiated NSPCs in the dentate gyrus was completely restored by grafted NSPCs in the dorsal, but not the ventral, blade. The grafted NSPCs did not exert appreciable effects on the endogenous NSPCs; however, more than half of the grafted NSPCs differentiated. These results point to novel strategies aimed at ameliorating the debilitating late effects of cranial radiotherapy, particularly in children.

Neurocognitive and Psychosocial Outcomes in Pediatric Brain Tumor Survivors

The late neurocognitive and psychosocial effects of treatment for pediatric brain tumor (PBT) represent important areas of clinical focus and ongoing research. Neurocognitive sequelae and associated problems with learning and socioemotional development negatively impact PBT survivors' overall health-related quality of life, educational attainment and employment rates. Multiple factors including tumor features and associated complications, treatment methods, individual protective and vulnerability factors and accessibility of environmental supports contribute to the neurocognitive and psychosocial outcomes in PBT survivors. Declines in overall measured intelligence are common and may persist years after treatment. Core deficits in attention, processing speed and working memory are postulated to underlie problems with overall intellectual development, academic achievement and career attainment. Additionally, psychological problems after PBT can include depression, anxiety and psychosocial adjustment issues. Several intervention paradigms are briefly described, though to date research on innovative, specific and effective interventions for neurocognitive late effects is still in its early stages. This article reviews the existing research for understanding PBT late effects and highlights the need for innovative research to enhance neurocognitive and psychosocial outcomes in PBT survivors.

Association of Neuronal Injury in the Genu and Body of Corpus Callosum After Cranial Irradiation in Children With Impaired Cognitive Control: A Prospective Study

PURPOSE

Brain radiation is associated with functional deficits in children. The purpose of this study was to examine white matter integrity as measured by diffusion tensor imaging and associations with region-specific radiation dose and neuropsychological functioning in children treated with cranial irradiation.

METHODS AND MATERIALS

A total of 20 patients and 55 age- and sex-matched controls were included in the present study. Diffusion tensor imaging and neuropsychological assessments were conducted at baseline and 6, 15, and 27 months after treatment. The neuropsychological assessment included motor dexterity, working memory, and processing speed. White matter regions were contoured, and the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were recorded for each participant. Linear mixed effects regression models were used to prospectively compare the associations among ADC, FA, radiation dose to contoured structures, and performance on the neuropsychological assessments over time.

RESULTS

The mean prescription dose was 44 Gy (range 12-54). Across visits, compared with the controls, the patients showed a significantly increased ADC across all selected regions and alterations in FA in the dorsal midbrain and corpus callosum (genu, splenium, body). An increased radiation dose to the genu and body of the corpus callosum was associated with alterations in ADC and FA and reduced neuropsychological performance, most notably motor speed and processing.

CONCLUSIONS

These prospective data suggest that subcortical white matter, especially the genu and body of the corpus callosum, could be regions with increased susceptibility to radiation-induced injury, with implications for cognitive function.

Hippocampal sparing in stereotactic radiotherapy for brain metastases: To contour or not contour the hippocampus?

PURPOSE

The aim of our study was to evaluate hippocampal irradiation in patients treated with fractionated stereotactic brain radiotherapy.

PATIENTS AND METHODS

Retrospective hippocampal dosimetric analysis performed on 22 patients with one to four brain metastases treated with fractionated stereotactic radiotherapy using volumetric intensity-modulated arc therapy. Original plans did not include hippocampus as avoidance structure in optimization criteria; hippocampus was retrospectively delineated on magnetic resonance coregistered with planning CT and using as reference the RTOG 0933 atlas. Hippocampus was defined both as a single and as pair organ. Constraints analysed were: Dmax<16Gy, D40%<7.3Gy, D100%=Dmin<9Gy. Assuming a α/β ratio of 2Gy, biologically equivalent dose in 2Gy fractions was calculated. Hippocampal-sparing plans were developed in cases where hippocampal constraints were not respected in the original plan.

RESULTS

Among constraints analysed Dmax and D40% have been exceeded in ten out of 22 cases. The constraints were not respected in patients with more than one metastatic lesion and in three patients with only one lesion. Considering all exceeded constraints values in non-hippocampal sparing plans, the 50% of them was respected after replanning. No significant differences were found among conformity and homogeneity index between non-hippocampal sparing and hippocampal sparing plans.

CONCLUSION

Volumetric intensity-modulated arc therapy hippocampal sparing plans significantly decreases dose to hippocampus assuring an equal target coverage and organs at risk avoiding.

A role for endothelial cells in radiation-induced inflammation

PURPOSE

To unravel the role of the vasculature in radiation-induced brain tissue damage.

MATERIALS AND METHODS

Postnatal day 14 mice received a single dose of 10 Gy cranial irradiation and were sacrificed 6 h, 24 h or 7 days post-irradiation. Endothelial cells were isolated from the hippocampus and cerebellum using fluorescence-activated cell sorting, followed by cell cycle analysis and gene expression profiling.

RESULTS

Flow cytometric analysis revealed that irradiation increased the percentage of endothelial cells, relative to the whole cell population in both the hippocampus and the cerebellum. This change in cell distribution indicates that other cell types are more susceptible to irradiation-induced cell death, compared to endothelial cells. This was supported by data showing that genes involved in endothelial cell-specific apoptosis (e.g. Smpd1) were not induced at any time point investigated but that genes involved in cell-cycle arrest (e.g. Cdkn1a) were upregulated at all investigated time points, indicating endothelial cell repair. Inflammation-related genes, on the other hand, were strongly induced, such as Ccl2, Ccl11 and Il6.

CONCLUSIONS

We conclude that endothelial cells are relatively resistant to ionizing radiation but that they play an active, hitherto unknown, role in the inflammatory response after irradiation. In the current study, this was shown in both the hippocampus, where neurogenesis and extensive cell death after irradiation occurs, and in the cerebellum, where neurogenesis no longer occurs at this developmental age.

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

Pediatric posterior fossa tumor (PFT) survivors who have been treated with cranial radiation therapy often suffer from cognitive impairments that might relate to IQ decline. Radiotherapy (RT) distinctly affects brain regions involved in different cognitive functions. However, the relative contribution of regional irradiation to the different cognitive impairments still remains unclear. We investigated the relationships between the changes in different cognitive scores and radiation dose distribution in 30 children treated for a PFT. Our exploratory analysis was based on a principal component analysis (PCA) and an ordinary least square regression approach. The use of a PCA was an innovative way to cluster correlated irradiated regions due to similar radiation therapy protocols across patients. Our results suggest an association between working memory decline and a high dose (equivalent uniform dose, EUD) delivered to the orbitofrontal regions, whereas the decline of processing speed seemed more related to EUD in the temporal lobes and posterior fossa. To identify regional effects of RT on cognitive functions may help to propose a rehabilitation program adapted to the risk of cognitive impairment.

Home sweet home: the neural stem cell niche throughout development and after injury

Neural stem cells and their progeny reside in two distinct neurogenic niches within the mammalian brain: the subventricular zone and the dentate gyrus. The interplay between the neural stem cells and the niche in which they reside can have significant effects on cell kinetics and neurogenesis. A comprehensive understanding of the changes to the niche that occur through postnatal development and aging, as well as following injury, is relevant for developing therapeutics and interventions to promote neural repair. We discuss changes that occur within the neural stem and progenitor cell populations, the vasculature, extracellular matrix, microglia, and secreted proteins through aging which impact cell behavior within the neurogenic niches. We examine neural precursor cell and niche responses to injury in neonatal hypoxia-ischemia, juvenile cranial irradiation, and adult stroke. This review examines the interplay between the niche and stem cell behavior through aging and following injury as a means to understand intrinsic and extrinsic factors that regulate neurogenesis in vivo.