Radiation Necrosis in Pediatric Patients with Brain Tumors Treated with Proton Radiotherapy

Systematic review of MRI alterations in the brain following proton and photon radiation therapy: Towards a uniform European Particle Therapy Network (EPTN) definition

Magnetic resonance imaging (MRI) often demonstrates alterations following cranial radiotherapy (RT), which may result in clinical symptoms and diagnostic uncertainty, and thus potentially impact treatment decisions. The potential differences in MRI alterations after proton and photon RT, has raised concerns regarding the relative biological effectiveness of proton therapy. To provide an overview of MRI alterations in the brain post-RT and to explore differences between photon and proton RT, a systematic review adhering to the PRISMA guidelines was conducted, focusing on the assessment methods and definitions across studies. A systematic search of three electronic databases was performed using the concepts 'normo-fractionated radiotherapy ', 'MRI alterations' and 'brain, skull base or head and neck tumours in adult and paediatric populations'. Data extraction and quality assessment was performed on articles meeting the predefined criteria by two independent reviewers. Out of 5887 screened studies, 94 met the inclusion criteria. These studies were categorized based on confinement of the MRI alterations to temporal lobe, brainstem, or across the entire brain. Additional subclassification was performed based on MRI sequences evaluated or by the nature of the alterations, with pseudoprogression generally reserved for glioma patients. While many papers exist on MRI alterations in the brain after RT, this review highlights significant inconsistencies in the terminology and definitions, limiting the comparability of findings across studies. Our results highlight the need for and facilitate the development of a standardized framework for describing MRI alterations after RT.

Particle Therapy to Overcome Cancer Radiation Resistance: "ARCHADE" Consortium Updates in Radiation Biology

Radiation therapy is a medical treatment that uses high doses of radiation to kill or damage cancer cells. It works by damaging the DNA within the cancer cells, ultimately causing cell death. Radiotherapy can be used as a primary treatment, adjuvant treatment in combination with surgery or chemotherapy or palliative treatment to relieve symptoms in advanced cancer stages. Radiation therapy is constantly improving in order to enhance the effect on cancer cells and reduce the side effects on healthy tissues. Our results clearly demonstrate that proton therapy and, even more, carbon ion therapy appear as promising alternatives to overcome the radioresistance of various tumors thanks to less dependency on oxygen and a better ability to kill cancer stem cells. Interestingly, hadrons also retain the advantages of radiosensitization approaches. These data confirm the great ability of hadrons to spare healthy tissue near the tumor via various mechanisms (reduced lymphopenia, bystander effect, etc.). Technology and machine improvements such as image-guided radiotherapy or particle therapies can improve treatment quality and efficacy (dose deposition and biological effect) in tumors while increasingly sparing healthy tissues. Radiation biology can help to understand how cancer cells resist radiation (hypoxia, DNA repair mechanisms, stem cell status, cell cycle position, etc.), how normal tissues may display sensitivity to radiation and how radiation effects can be increased with either radiosensitizers or accelerated particles. All these research topics are under investigation within the ARCHADE research community in France. By focusing on these areas, radiotherapy can become more effective, targeted and safe, enhancing the overall treatment experience and outcomes for cancer patients. Our goal is to provide biological evidence of the therapeutic advantages of hadrontherapy, according to the tumor characteristics. This article aims to give an updated view of our research in radiation biology within the frame of the French "ARCHADE association" and new perspectives on research and treatment with the C400 multi-ions accelerator prototype.

The Association of Linear Energy Transfer and Dose With Radiation Necrosis After Pencil Beam Scanning Proton Therapy in Pediatric Posterior Fossa Tumors

PURPOSE

Proton therapy is the preferred treatment modality for most pediatric central nervous system tumors. The risk of radiation necrosis may be increased at the distal end of the beam because of an increase in linear energy transfer (LET) and relative biological effectiveness (RBE) dose. We report on the association of LET and dose with radiation necrosis after pencil beam scanning proton therapy in pediatric posterior fossa tumors using a case-control framework.

MATERIALS AND METHODS

From 2019 to 2022, 33 patients less than or equal to 18 years of age treated with first-line proton therapy for primary tumors in the posterior fossa and with 6 or more months of follow-up magnetic resonance imaging were retrospectively identified. Nine patients with imaging changes consistent with necrosis were matched with controls in a 1:2 fashion based on age, sex, dose, and follow-up time from proton therapy. Dose (Gy [RBE]) and dose-averaged LET (LETd) values for target structures and organs at risk were computed and compared between cases and controls.

RESULTS

Within the whole cohort, the mean age was 6.6 years (SD, 4.77) with a median follow-up time of 24.1 months. Within the case-control matched cohort (18 controls and 9 cases), there were no significant differences in age, sex, time to follow-up, tumor location, dose, and use of concurrent chemotherapy. The mean time to necrotic imaging finding was 4.47 months (SD, 2.03). Cases demonstrated significantly higher brainstem D50 (P = .02). LETd was not different between cases and controls. However, when using a combined metric of higher brainstem dose {>47.5 (Gy [RBE])} and higher LETd (>3.5 keV/µm), a greater proportion of cases compared with controls met this metric (89% vs 39%, P = .02).

CONCLUSIONS

Combined effects of intermediate-to-high dose and LETd in the brainstem may contribute to greater necrosis risk after pencil beam scanning proton therapy in children with posterior fossa tumors.

Radiological Predictors of Cognitive Impairment in Paediatric Brain Tumours Using Multiparametric Magnetic Resonance Imaging: A Review of Current Practice, Challenges and Future Directions

Paediatric brain tumours and their treatments are associated with long-term cognitive impairment. While the aetiology of cognitive impairment is complex and multifactorial, multiparametric Magnetic Resonance Imaging (MRI) can identify many risk factors including tumour location, damage to eloquent structures and tumour phenotype. Hydrocephalus and raised intracranial pressure can be observed, along with risk factors for post-operative paediatric cerebellar mutism syndrome or epilepsy. MRI can also identify complications of surgery or radiotherapy and monitor treatment response. Advanced imaging sequences provide valuable information about tumour and brain physiology, but clinical use is limited by extended scanning times and difficulties in processing and analysis. Brain eloquence classifications exist, but focus on adults with neurological deficits and are outdated. For the analysis of childhood tumours, limited numbers within tumour subgroups and the investigation of long-term outcomes necessitate using historical scans and/or multi-site collaboration. Variable imaging quality and differing acquisition parameters limit the use of segmentation algorithms and radiomic analysis. Harmonisation can standardise imaging in collaborative research, but can be challenging, while data-sharing produces further logistical challenges. Consequently, most research consists of small single-centre studies limited to regional analyses of tumour location. Technological advances reducing scanning times increase the feasibility of clinical acquisition of high-resolution standardised imaging including advanced physiological sequences. The RAPNO and SIOPE paediatric brain tumour imaging guidelines have improved image standardisation, which will benefit future collaborative imaging research. Modern machine learning techniques provide more nuanced approaches for integration and analysis of the complex and multifactorial data involved in cognitive outcome prediction.

Aberrant choroid plexus formation drives the development of treatment-related brain toxicity

Brain tumors are commonly treated with radiotherapy, but the efficacy of the treatment is limited by its toxicity to the normal tissue including post-irradiation contrast enhanced lesions often linked to necrosis. The poorly understood mechanisms behind such brain lesions were studied using cerebral organoids. Here we show that irradiation of such organoids leads to dose-dependent growth retardation and formation of liquid-filled cavities but is not correlated with necrosis. Instead, the radiation-induced changes comprise of an enhancement of cortical hem markers, altered neuroepithelial stem cell differentiation, and an increase of ZO1+/AQP1+/CLDN3+-choroid plexus (CP)-like structures accompanied by an upregulation of IGF2 mRNA, known to be expressed in CP and cerebrospinal fluid. The altered differentiation is attributed to changes in the WNT/BMP signaling pathways. We conclude that aberrant CP formation can be involved in radiation-induced brain lesions providing additional strategies for possible countermeasures.

CyberKnife in Pediatric Oncology: A Narrative Review of Treatment Approaches and Outcomes

Pediatric cancers, while rare, pose unique challenges due to the heightened sensitivity of developing tissues and the increased risk of long-term radiation-induced effects. Radiotherapy (RT) is a cornerstone in pediatric oncology, but its application is limited by concerns about toxicity, particularly secondary malignancies, growth abnormalities, and cognitive deficits. CyberKnife (CK), an advanced robotic radiosurgery system, has emerged as a promising alternative due to its precision, non-invasiveness, and ability to deliver hypofractionated, high-dose RT while sparing healthy tissues. This narrative review explores the existing evidence on CK application in pediatric patients, synthesizing data from case reports, small series, and larger cohort studies. All the studies analyzed reported cases of tumors located in the skull or in the head and neck region. Findings suggest CK's potential for effective tumor control with favorable toxicity profiles, especially for complex or inoperable tumors. However, the evidence remains limited, with the majority of studies involving small sample sizes and short follow-up periods. Moreover, concerns about the "dose-bath" effect and limited long-term data on stochastic risks warrant cautious adoption. Compared to Linac-based RT and proton therapy, CK offers unique advantages in reducing session numbers and enhancing patient comfort, while its real-time tracking provides superior accuracy. Despite these advantages, CK is associated with significant limitations, including a higher potential for low-dose scatter (often referred to as the "dose-bath" effect), extended treatment times in some protocols, and high costs requiring specialized expertise for operation. Emerging modalities like π radiotherapy further underscore the need for comparative studies to identify the optimal technique for specific pediatric cases. Notably, proton therapy remains the benchmark for minimizing long-term toxicity, but its cost and availability limit its accessibility. This review emphasizes the need for balanced evaluations of CK and highlights the importance of planning prospective studies and long-term follow-ups to refine its role in pediatric oncology. A recent German initiative to establish a CK registry for pediatric CNS lesions holds significant promise for advancing evidence-based applications and optimizing treatment strategies in this vulnerable population.

NRG Oncology White Paper on the Relative Biological Effectiveness in Proton Therapy

This position paper, led by the NRG Oncology Particle Therapy Work Group, focuses on the concept of relative biologic effect (RBE) in clinical proton therapy (PT), with the goal of providing recommendations for the next-generation clinical trials with PT on the best practice of investigating and using RBE, which could deviate from the current standard proton RBE value of 1.1 relative to photons. In part 1, current clinical utilization and practice are reviewed, giving the context and history of RBE. Evidence for variation in RBE is presented along with the concept of linear energy transfer (LET). The intertwined nature of tumor radiobiology, normal tissue constraints, and treatment planning with LET and RBE considerations is then reviewed. Part 2 summarizes current and past clinical data and then suggests the next steps to explore and employ tools for improved dynamic models for RBE. In part 3, approaches and methods for the next generation of prospective clinical trials are explored, with the goal of optimizing RBE to be both more reflective of clinical reality and also deployable in trials to allow clinical validation and interpatient comparisons. These concepts provide the foundation for personalized biologic treatments reviewed in part 4. Finally, we conclude with a summary including short- and long-term scientific focus points for clinical PT. The practicalities and capacity to use RBE in treatment planning are reviewed and considered with more biological data in hand. The intermediate step of LET optimization is summarized and proposed as a potential bridge to the ultimate goal of case-specific RBE planning that can be achieved as a hypothesis-generating tool in near-term proton trials.

Future Directions in the Treatment of Low-Grade Gliomas

ABSTRACT

There is major interest in deintensifying therapy for isocitrate dehydrogenase-mutant low-grade gliomas, including with single-agent cytostatic isocitrate dehydrogenase inhibitors. These efforts need head-to-head comparisons with proven modalities, such as chemoradiotherapy. Ongoing clinical trials now group tumors by intrinsic molecular subtype, rather than classic clinical risk factors. Advances in imaging, surgery, and radiotherapy have improved outcomes in low-grade gliomas. Emerging biomarkers, targeted therapies, immunotherapy, radionuclides, and novel medical devices are a promising frontier for future treatment. Diverse representation in glioma research and clinical trials will help to ensure that advancements in care are realized by all groups.

The current state of proton radiotherapy

Radiotherapy is indicated for nearly all cancers and at all stages in one form or another. More than half of all cancer patients are treated with radiation at some point in their cancer treatment. Conventional X-ray (photon) based radiotherapy does have a number of physical limitations which were theorized to be overcome by instead employing proton based radiotherapy. The late 1990s and early 2000s saw a rapid adoption in proton therapy as many speculated a greatly improved therapeutic window compared with photon therapy. Only a few randomized clinical trials have been reported, but to-date proton therapy has not shown to improve cancer control metrics. There is improved treatment related toxicity which may be clinically meaningful in some scenarios, but further expansion and wide spread utilization of the technology may be drastically limited by the substantially higher start up and operational costs of a proton center. Nonetheless, proton therapy may be beneficial in select scenarios which warrant individualized consideration.

Evolution of Proton Radiation Therapy Brainstem Constraints on the Pediatric Proton/Photon Consortium Registry

PURPOSE

Increasing concern that brainstem toxicity incidence after proton radiation therapy might be higher than with photons led to a 2014 University of Florida (UF) landmark paper identifying its risk factors and proposing more conservative dose constraints. We evaluated how practice patterns changed among the Pediatric Proton/Photon Consortium Registry (PPCR).

MATERIAL AND METHODS

This prospective multicenter cohort study gathered data from patients under the age of 22 years enrolled on the PPCR, treated between 2002 and 2019 for primary posterior fossa brain tumors. After standardizing brainstem contours, we garnered dosimetry data and correlated those meeting the 2014 proton-specific brainstem constraint guidelines by treatment era, histology, and extent of surgical resection.

RESULTS

A total of 467 patients with evaluable proton radiation therapy plans were reviewed. Median age was 7.1 years (range: <1-21.9), 63.0% (n = 296) were men, 76.0% (n = 357) were White, and predominant histology was medulloblastoma (55.0%, n = 256), followed by ependymoma (27.0%, n = 125). Extent of resection was mainly gross total resection (GTR) (67.0%, n = 312), followed by subtotal resection (STR) or biopsy (20.0%, n = 92), and near total resection (NTR) (9.2%, n = 43). The UF brainstem constraint metrics most often exceeded were the goal D50% of 52.4 gray relative biological equivalents (43.3%, n = 202) and maximal D50% of 54 gray relative biological equivalents (12.6%, n = 59). The compliance rate increased after the new guidelines (2002-2014: 64.0% vs 2015-2019: 74.6%, P = .02), except for ependymoma (46.3% pre- vs 50.0% post-guidelines, P = .86), presenting lower compliance (48.8%) in comparison to medulloblastoma/ primitive neuroectodermal tumors/pineoblastoma (77.7%), glioma (89.1%), and atypical teratoid/rhabdoid tumors (90.9%) (P < .001). Degree of surgical resection did not affect compliance rates (GTR/NTR 71.0% vs STR/biopsy 72.8%, P = .45), even within the ependymoma subset (GTR/NTR 50.5% vs STR/biopsy 38.1%, P = .82).

CONCLUSION

Since the publication of the UF guidelines, the pediatric proton community has implemented more conservative brainstem constraints in all patients except those with ependymoma, irrespective of residual disease after surgery. Future work will evaluate if this change in practice is associated with decreased rates of brainstem toxicity.

Brainstem Toxicity Following Proton Beam Radiation Therapy in Pediatric Brain Tumors: A Systematic Review and Meta-Analysis

Background: Proton beam radiation therapy (PBRT) is an advanced cancer treatment modality that utilizes the distinctive physical properties of protons to precisely deliver radiation to tumor targets while sparing healthy tissue. This cannot be obtained with photon radiation. In this systematic review and meta-analysis, we aimed to comprehensively assess the risk of brainstem toxicity in pediatric brain tumor patients undergoing PBRT. Methods: With adherence to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a predetermined search strategy was used to identify eligible articles from PubMed, Web of Science, Scopus, and Cochrane Library through July 2024. Results: The current study included a total of 11 eligible articles. The pooled prevalence of patients who suffered from brainstem toxicity was 1.8% (95% CI: 1%, 2.6%). The pooled prevalences of patients with Grade 1 to Grade 5 brainstem toxicity were found to be 10.6% (95% CI: 8.8%, 30%), 1.5% (95% CI: 0.6%, 2.5%), 0.7% (95% CI: 0.3%, 1.1%), 0.4% (95% CI: 0.1%, 0.7%), and 0.4% (95% CI: 0.1%, 0.8%), respectively, with an overall pooled prevalence of 0.7% (95% CI: 0.4%, 1%). Conclusions: This study revealed a relatively low incidence of symptomatic brainstem toxicity and its related mortality in the pediatric population undergoing PBRT. However, further research is encouraged to study the broader effects of PBRT and to explore various factors that may influence the risk of brainstem toxicity in patients treated with PBRT.

Intensive Interdisciplinary Rehabilitation in the Pediatric Hematology/Oncology Setting: Feasibility and Perceived Benefit of the Acute Neurological Injury Service

(1) Background: Intensive interdisciplinary rehabilitation services more effectively promote recovery from acquired brain injury than a single discipline approach. However, research literature is lacking regarding the perceived feasibility and utility of an interdisciplinary approach across disciplines for patients within a tertiary care pediatric hematology/oncology setting. (2) Methods: The Acute Neurological Injury (ANI) service applied an acquired brain injury/inpatient rehabilitation interdisciplinary approach to a pediatric hematology/oncology population, with a focus on interdisciplinary communication, shared goal setting, and coordinated transition planning. Caregivers whose children received coordinated ANI program care were interviewed regarding the perceived feasibility and utility of ANI program components. (3) Results: An interdisciplinary approach to a pediatric hematology/oncology population is feasible for caregivers and for providers of rehabilitation and psychosocial services within a tertiary care cancer hospital setting. Parents perceived benefits from aspects of this approach including coordinated interdisciplinary care planning, the implementation of an interdisciplinary goal, parent brain injury education, neuropsychological assessment reports, and weekly cognitive intervention sessions. Parents were interested in both having a peer mentor while managing new cancer diagnoses and later serving in a mentor role for a newly diagnosed family. (4) Conclusions: An interdisciplinary acquired brain injury approach to a pediatric hematology/oncology population is feasible with perceived benefits to families managing new cancer diagnoses.

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.

Brain and Brain Stem Necrosis After Reirradiation for Recurrent Childhood Primary Central Nervous System Tumors: A PENTEC Comprehensive Review

PURPOSE

Reirradiation is increasingly used in children and adolescents/young adults (AYA) with recurrent primary central nervous system tumors. The Pediatric Normal Tissue Effects in the Clinic (PENTEC) reirradiation task force aimed to quantify risks of brain and brain stem necrosis after reirradiation.

METHODS AND MATERIALS

A systematic literature search using the PubMed and Cochrane databases for peer-reviewed articles from 1975 to 2021 identified 92 studies on reirradiation for recurrent tumors in children/AYA. Seventeen studies representing 449 patients who reported brain and brain stem necrosis after reirradiation contained sufficient data for analysis. While all 17 studies described techniques and doses used for reirradiation, they lacked essential details on clinically significant dose-volume metrics necessary for dose-response modeling on late effects. We, therefore, estimated incidences of necrosis with an exact 95% CI and qualitatively described data. Results from multiple studies were pooled by taking the weighted average of the reported crude rates from individual studies.

RESULTS

Treated cancers included ependymoma (n = 279 patients; 7 studies), medulloblastoma (n = 98 patients; 6 studies), any CNS tumors (n = 62 patients; 3 studies), and supratentorial high-grade gliomas (n = 10 patients; 1 study). The median interval between initial and reirradiation was 2.3 years (range, 1.2-4.75 years). The median cumulative prescription dose in equivalent dose in 2-Gy fractions (EQD22; assuming α/β value = 2 Gy) was 103.8 Gy (range, 55.8-141.3 Gy). Among 449 reirradiated children/AYA, 22 (4.9%; 95% CI, 3.1%-7.3%) developed brain necrosis and 14 (3.1%; 95% CI, 1.7%-5.2%) developed brain stem necrosis with a weighted median follow-up of 1.6 years (range, 0.5-7.4 years). The median cumulative prescription EQD22 was 111.4 Gy (range, 55.8-141.3 Gy) for development of any necrosis, 107.7 Gy (range, 55.8-141.3 Gy) for brain necrosis, and 112.1 Gy (range, 100.2-117 Gy) for brain stem necrosis. The median latent period between reirradiation and the development of necrosis was 5.7 months (range, 4.3-24 months). Though there were more events among children/AYA undergoing hypofractionated versus conventionally fractionated reirradiation, the differences were not statistically significant (P = .46).

CONCLUSIONS

Existing reports suggest that in children/AYA with recurrent brain tumors, reirradiation with a total EQD22 of about 112 Gy is associated with an approximate 5% to 7% incidence of brain/brain stem necrosis after a median follow-up of 1.6 years (with the initial course of radiation therapy being given with conventional prescription doses of ≤2 Gy per fraction and the second course with variable fractionations). We recommend a uniform approach for reporting dosimetric endpoints to derive robust predictive models of late toxicities following reirradiation.

Evolving Role of Proton Radiation Therapy in Clinical Practice

With the expansion of proton radiation therapy centers across the United States and a gradually expanding body of academic evidence supporting its use, more patients are receiving-and asking about-proton therapy than ever before. Here, we outline, for nonradiation oncologists, the theoretical benefits of proton therapy, the clinical evidence to date, the controversies affecting utilization, and the numerous randomized trials currently in progress. We also discuss the challenges of researching and delivering proton therapy, including the cost of constructing and maintaining centers, barriers with insurance approval, clinical situations in which proton therapy may be approached with caution, and the issue of equitable access for all patients. The purpose of this review is to assist practicing oncologists in understanding the evolving role of proton therapy and to help nonradiation oncologists guide patients regarding this technology.

Evaluation of specific RBE in different cells of hippocampus under high-dose proton irradiation in rats

The study aimed to determine the specific relative biological effectiveness (RBE) of various cells in the hippocampus following proton irradiation. Sixty Sprague-Dawley rats were randomly allocated to 5 groups receiving 20 or 30 Gy of proton or photon irradiation. Pathomorphological neuronal damage in the hippocampus was assessed using Hematoxylin-eosin (HE) staining. The expression level of NeuN, Nestin, Caspase-3, Olig2, CD68 and CD45 were determined by immunohistochemistry (IHC). The RBE range established by comparing the effects of proton and photon irradiation at equivalent biological outcomes. Proton20Gy induced more severe damage to neurons than photon20Gy, but showed no difference compared to photon30Gy. The RBE of neuron was determined to be 1.65. Similarly, both proton20Gy and proton30Gy resulted in more inhibition of oligodendrocytes and activation of microglia in the hippocampal regions than photon20Gy and photon30Gy. However, the expression of Olig2 was higher and CD68 was lower in the proton20Gy group than in the photon30Gy group. The RBE of oligodendrocyte and microglia was estimated to be between 1.1 to 1.65. For neural stem cells (NSCs) and immune cells, there were no significant difference in the expression of Nestin and CD45 between proton and photon irradiation (both 20 and 30 Gy). Therefore, the RBE for NSCs and immune cell was determined to be 1.1. These findings highlight the varying RBE values of different cells in the hippocampus in vivo. Moreover, the actual RBE of the hippocampus may be higher than 1.1, suggesting that using as RBE value of 1.1 in clinical practice may underestimate the toxicities induced by proton radiation.

Radiation-Induced Cerebral Contrast Enhancements Strongly Share Ischemic Stroke Risk Factors

PURPOSE

Radiation-induced cerebral contrast enhancements (RICE) are frequent after photon and particularly proton radiation therapy and are associated with a significant risk for neurologic morbidity. Nevertheless, risk factors are poorly understood. A more robust understanding of RICE risk factors is crucial to improve management and offer adaptive therapy at the outset and during follow-up.

METHODS AND MATERIALS

We analyzed the comorbidities in detail of 190 consecutive adult patients treated at a single European national comprehensive cancer center with proton radiation therapy (54 Gy relative biological effectiveness) for LGG from 2010 to 2020 who were followed with serial clinical examinations and magnetic resonance imaging for a median 5.6 years.

RESULTS

Classical vascular risk factors including age (≥50 vs <50 years: 1.6-fold; P = .0024), hypertension (2.7-fold; P = .00012), and diabetes (11.7-fold; P = .0066) were observed more frequently in the cohort that developed RICE. Dyslipidemia (2.1-fold), being overweight (2.0-fold), and smoking (2.6-fold), as well as history of previous stroke (1.7-fold), were also more frequently observed in the RICE cohort, although these factors did not reach the threshold for significance. Multivariable regression modeling supported the influence of age (P = .05), arterial hypertension (P = .01), and potentially male sex (P = .02), diabetes (P = .0008), and smoking (P = .001) on RICE occurrence over time, independent of each other and further vascular risk factors. If RICE occurred, bevacizumab treatment was 2-fold more frequently needed in the cohort with vascular risk factors, but RICE long-term prognosis did not differ between the RICE subcohorts with and without vascular risk factors.

CONCLUSIONS

This is the first report in the literature demonstrating that RICE strongly shares vascular risk factors with ischemic stroke, which further enhances the nebulous understanding of the multifactorial pathophysiology of RICE. Classical vascular risk factors, especially age, hypertension, and diabetes, clearly correlated independently with RICE risk. Risk-adapted screening and management for RICE can be directly derived from these data to assist in clinical management.

Excessively Delayed Radiation Changes After Proton Beam Therapy for Brain Tumors: Report of Two Cases

Delayed cerebral necrosis is a well-known complication of radiation therapy (RT). Because of its irreversible nature, it should be avoided if possible, but avoidance occurs at the expense of potentially compromised tumor control, despite the use of the modern advanced technique of conformal RT that minimizes radiation to normal brain tissue. Risk factors for radiation-induced cerebral necrosis include a higher dose per fraction, larger treatment volume, higher cumulative dose, and shorter time interval (for re-irradiation). The same principle can be applied to proton beam therapy (PBT) to avoid delayed cerebral necrosis. However, conversion of PBT radiation energy into conventional RT is still short of clinical support, compared to conventional RT. Herein, we describe two patients with excessively delayed cerebral necrosis after PBT, in whom follow-up MRI showed no RT-induced changes prior to 3 years after treatment. One patient developed radiation necrosis at 4 years after PBT to the resection cavity of an astroblastoma, and the other developed brainstem necrosis that became symptomatic 6 months after its first appearance on the 3-year follow-up brain MRI. We also discuss possible differences between radiation changes after PBT versus conventional RT.

Prospective Analysis of Radiation-Induced Contrast Enhancement and Health-Related Quality of Life After Proton Therapy for Central Nervous System and Skull Base Tumors

PURPOSE

Intracerebral radiation-induced contrast enhancement (RICE) can occur after photon as well as proton beam therapy (PBT). This study evaluated the incidence, characteristics, and risk factors of RICE after PBT delivered to, or in direct proximity to, the brain and its effect on health-related quality of life (HRQoL).

METHODS AND MATERIALS

Four hundred twenty-one patients treated with pencil beam scanning PBT between 2017 and 2021 were included. Follow-up included clinical evaluation and contrast-enhanced magnetic resonance imaging at 3, 6, and 12 months after treatment completion and annually thereafter. RICE was graded according to Common Terminology Criteria for Adverse Events version 4, and HRQoL parameters were assessed via European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ)-C30 questionnaires.

RESULTS

The median follow-up was 24 months (range, 6-54), and median dose to 1% relative volume of noninvolved central nervous system (D1%CNS) was 54.3 Gy relative biologic effectiveness (RBE; range, 30-76 Gy RBE). The cumulative RICE incidence was 15% (n = 63), of which 10.5% (n = 44) were grade 1, 3.1% (n = 13) were grade 2, and 1.4% (n = 6) were grade 3. No grade 4 or 5 events were observed. Twenty-six of 63 RICE (41.3%) had resolved at the latest follow-up. The median onset after PBT and duration of RICE in patients in whom the lesions resolved were 11.8 and 9.0 months, respectively. On multivariable analysis, D1%CNS > 57.6 Gy RBE, previous in-field radiation, and diabetes mellitus were identified as significant risk factors for RICE development. Previous radiation was the only factor influencing the risk of symptomatic RICE. After PBT, general HRQoL parameters were not compromised. In a matched cohort analysis of 54/50 patients with and without RICE, no differences in global health score or functional and symptom scales were seen.

CONCLUSIONS

The overall incidence of clinically relevant RICE after PBT is very low and has no significant negative effect on long-term patient QoL.

Somatic Versus Germline: A Case Series of Three Children With ATM-Mutated Medulloblastoma

Somatic versus Germline-A Case Series of Three Children with ATM- mutated Medulloblastoma.

Current Molecular and Clinical Landscape of ATRT - The Link to Future Therapies

ATRT is a highly aggressive and rare pediatric CNS tumor of very young children. Its genetic hallmark is bi-allelic inactivation of SMARCB1 encoding INI1. Rarely SMARCA4 encoding BRG1 is affected. Up to 30% are associated with constitutional heterozygous pathogenic variants in one of the two genes, giving rise to the Rhabdoid-Tumor-Predisposition-Syndromes (RTPS) 1 and 2. Characteristic DNA methylation profiles distinguish ATRT from other SMARCB1-deficient entities. Three distinct subtypes ATRT-MYC, -TYR, and -SHH are on record. ATRT-SHH may be further divided into the subgroups ATRT-SHH1A, -SHH1B, and -SHH2. The cure of ATRT remains challenging, notwithstanding an increasing understanding of molecular pathomechanisms and genetic background. The implementation of multimodal institutional treatment protocols has improved prognosis. Regardless of treatment approaches, clinical risk factors such as age, metastases, and DNA methylation subtype affect survival probability. We provide a critical appraisal of current conventional multimodal regimens and emerging targeted treatment approaches investigated in clinical trials and entity-specific registries. Intense treatment approaches featuring radiotherapy (RT) and high-dose chemotherapy (HDCT) face the difficulty of balancing tumor control and treatment-related toxicity. Current approaches focus on minimizing radiation fields by proton beam therapy or to withhold RT in HDCT-only approaches. Still, a 40-75% relapse rate upon first-line treatment reveals the need for novel treatment strategies in primary and even more in recurrent/refractory (r/r) disease. Among targeted treatments, immune checkpoint inhibitors and epigenetically active agents appear most promising. Success remains limited in single agent approaches. We hypothesize that mechanism-informed combination therapy will enhance response, as the low mutational burden of ATRT may contribute to acquiring resistance to single targeted agents. As DNA methylation group-specific gene expression profiles appear to influence response to distinct agents, the future treatment of ATRT should respect clinical and biological heterogeneity in risk group adjusted treatment protocols.

Pediatric Neuro-oncology

OBJECTIVE

This article reviews the most common pediatric brain tumors, neurocutaneous syndromes, treatment-related neurotoxicities, and the long-term outcomes of survivors.

LATEST DEVELOPMENTS

In the era of molecular diagnostics, the classification, management, and prognostication of pediatric brain tumors and neurocutaneous syndromes has been refined, resulting in advancements in patient management. Molecular diagnostics have been incorporated into the most recent World Health Organization 2021 classification. This knowledge has allowed for novel therapeutic approaches targeting the biology of these tumors with the intent to improve overall survival, decrease treatment-related morbidity, and improve quality of life. Advances in management have led to better survival, but mortality remains high and significant morbidity persists. Current clinical trials focus on tumor biology targeted therapy, deescalation of therapy, and multimodal intensified approaches with targeted therapy in more high-risk tumors.

ESSENTIAL POINTS

Molecular diagnostics for pediatric brain tumors and neurocutaneous syndromes have led to novel therapeutic approaches targeting the biology of these tumors with the goals of improving overall survival and decreasing treatment-related morbidity. Further understanding will lead to continued refinement and improvement of tumor classification, management, and prognostication.

Delivery of re-irradiation and complex palliative radiotherapy using proton therapy in pediatric cancer patients

BACKGROUND

The intent of this study is to characterize indications for pediatric palliative-intent proton radiation therapy (PIPRT).

PROCEDURE

We retrospectively reviewed patients 21 years and younger who received PIPRT. We defined PIPRT as radiotherapy (RT) aimed to improve cancer-related symptoms/provide durable local control in the non-curative setting. Mixed proton/photon plans were included. Adjacent re-irradiation (reRT) was defined as a reRT volume within the incidental dose cloud of a prior RT target, whereas direct reRT was defined as in-field overlap with prior RT target. Acute toxicity during RT until first inspection visit was graded according to the Common Terminology Criteria for Adverse Events. The Kaplan-Meier method, measured from last PIPRT fraction, was used to assess progression-free survival (PFS) and overall survival (OS).

RESULTS

Eighteen patients underwent PIPRT between 2014 and 2020. Median age at treatment start was 10 years [2-21]. Median follow-up was 8.2 months [0-48]. Treatment sites included: brain/spine [10], abdomen/pelvis [3], thorax [3], and head/neck [2]. Indications for palliation included: durable tumor control [18], neurologic symptoms [4], pain [3], airway compromise [2], and great vessel compression [1]. Indications for protons included: reRT [15] (three adjacent, 12 direct), craniospinal irradiation [4], reduction of dose to normal tissues [3]. Sixteen experienced grade (G) 1-2 toxicity; two G3. There were no reports of radionecrosis. Median PFS was 5.3 months [95% confidence interval (CI): 2.7-16.3]. Median OS was 8.3 months [95% CI: 5.5-26.3].

CONCLUSIONS

The most common indication for PIPRT was reRT to provide durable tumor control. PIPRT appears to be safe, with no cases of high-grade toxicity.

Aberrant choroid plexus formation in human cerebral organoids exposed to radiation

Brain tumor patients are commonly treated with radiotherapy, but the efficacy of the treatment is limited by its toxicity, particularly the risk of radionecrosis. We used human cerebral organoids to investigate the mechanisms and nature of postirradiation brain image changes commonly linked to necrosis. Irradiation of cerebral organoids lead to increased formation of ZO1+/AQP1+/CLN3+-choroid plexus (CP) structures. Increased CP formation was triggered by radiation via the NOTCH/WNT signaling pathways and associated with delayed growth and neural stem cell differentiation, but not necrosis. The effect was more pronounced in immature than in mature organoids, reflecting the clinically-observed increased radiosensitivity of the pediatric brain. Protons were more effective than X-rays at the same dose, as also observed in clinical treatments. We conclude that radiation-induced brain image-changes can be attributed to aberrant CP formation, providing a new cellular mechanism and strategy for possible countermeasures.

From Bragg Peaks to Adaptive Fields-The Need for Evidence-Based Adoption of New Technologies in Radiotherapy

This Viewpoint discusses the need for multi-institutional prospective randomized trials of new technologies in radiotherapy to improve the therapeutic ratio and safety of radiotherapy treatments.

A Radiation Oncologist's Journey Through Technological Advancements in Oncology: Reflections on the Proton Therapy Winterschool at Paul Scherrer Institute, Switzerland

The proton therapy course at the Paul Scherrer Institute (PSI) in Switzerland provided a comprehensive insight into the clinical, physics, and technological aspects of proton therapy, with a particular focus on pencil beam scanning techniques. The program consisted of engaging lectures, hands-on workshops, and facility tours, which covered topics such as the history of proton therapy, treatment planning systems, clinical applications, and future developments. Participants gained practical experience with treatment planning and simulation, while also exploring the challenges associated with various tumor types and motion management. The collaborative and supportive learning environment fostered by the faculty and staff at PSI enriched the educational experience, empowering participants to better serve their patients in the field of radiation oncology.

Slice2Volume: Fusion of multimodal medical imaging and light microscopy data of irradiation-injured brain tissue in 3D

Comprehending cellular changes of radiation-induced brain injury is crucial to prevent and treat the pathology. We provide a unique open dataset of proton-irradiated mouse brains consisting of medical imaging, radiation dose simulations, and large-scale microscopy images, all registered into a common coordinate system. This allows dose-dependent analyses on single-cell level.

Analysis of safety and efficacy of proton radiotherapy for IDH-mutated glioma WHO grade 2 and 3

PURPOSE

Proton beam radiotherapy (PRT) has been demonstrated to improve neurocognitive sequelae particularly. Nevertheless, following PRT, increased rates of radiation-induced contrast enhancements (RICE) are feared. How safe and effective is PRT for IDH-mutated glioma WHO grade 2 and 3?

METHODS

We analyzed 194 patients diagnosed with IDH-mutated WHO grade 2 (n = 128) and WHO grade 3 (n = 66) glioma who were treated with PRT from 2010 to 2020. Serial clinical and imaging follow-up was performed for a median of 5.1 years.

RESULTS

For WHO grade 2, 61% were astrocytoma and 39% oligodendroglioma while for WHO grade 3, 55% were astrocytoma and 45% oligodendroglioma. Median dose for IDH-mutated glioma was 54 Gy(RBE) [range 50.4-60 Gy(RBE)] for WHO grade 2 and 60 Gy(RBE) [range 54-60 Gy(RBE)] for WHO grade 3. Five year overall survival was 85% in patients with WHO grade 2 and 67% in patients with WHO grade 3 tumors. Overall RICE risk was 25%, being higher in patients with WHO grade 2 (29%) versus in patients with WHO grade 3 (17%, p = 0.13). RICE risk increased independent of tumor characteristics with older age (p = 0.017). Overall RICE was symptomatic in 31% of patients with corresponding CTCAE grades as follows: 80% grade 1, 7% grade 2, 13% grade 3, and 0% grade 3 + . Overall need for RICE-directed therapy was 35%.

CONCLUSION

These data demonstrate the effectiveness of PRT for IDH-mutated glioma WHO grade 2 and 3. The RICE risk differs with WHO grading and is higher in older patients with IDH-mutated Glioma WHO grade 2 and 3.

Increased relative biological effectiveness and periventricular radiosensitivity in proton therapy of glioma patients

PURPOSE

Currently, there is an intense debate on variations in intra-cerebral radiosensitivity and relative biological effectiveness (RBE) in proton therapy of primary brain tumours. Here, both effects were retrospectively investigated using late radiation-induced brain injuries (RIBI) observed in follow-up after proton therapy of patients with diagnosed glioma.

METHODS

In total, 42 WHO grade 2-3 glioma patients out of a consecutive patient cohort having received (adjuvant) proton radio(chemo)therapy between 2014 and 2017 were eligible for analysis. RIBI lesions (symptomatic or clinically asymptomatic) were diagnosed and delineated on contrast-enhanced T1-weighted magnetic resonance imaging scans obtained in the first two years of follow-up. Correlation of RIBI location and occurrence with dose (D), proton dose-averaged linear energy transfer (LET) and variable RBE dose parameters were tested in voxel- and in patient-wise logistic regression analyses. Additionally, anatomical and clinical parameters were considered. Model performance was estimated through cross-validated area-under-the-curve (AUC) values.

RESULTS

In total, 64 RIBI lesions were diagnosed in 21 patients. The median time between start of proton radio(chemo)therapy and RIBI appearance was 10.2 months. Median distances of the RIBI volume centres to the cerebral ventricles and to the clinical target volume border were 2.1 mm and 1.3 mm, respectively. In voxel-wise regression, the multivariable model with D, D × LET and periventricular region (PVR) revealed the highest AUC of 0.90 (95 % confidence interval: 0.89-0.91) while the corresponding model without D × LET revealed a value of 0.84 (0.83-0.86). In patient-level analysis, the equivalent uniform dose (EUD₁₁, a = 11) in the PVR using a variable RBE was the most prominent predictor for RIBI with an AUC of 0.63 (0.32-0.90).

CONCLUSIONS

In this glioma cohort, an increased radiosensitivity within the PVR was observed as well as a spatial correlation of RIBI with an increased RBE. Both need to be considered when delivering radio(chemo)therapy using proton beams.

Proton Beam Therapy for Pediatric Tumors of the Central Nervous System-Experiences of Clinical Outcome and Feasibility from the KiProReg Study

As radiotherapy is an important part of the treatment in a variety of pediatric tumors of the central nervous system (CNS), proton beam therapy (PBT) plays an evolving role due to its potential benefits attributable to the unique dose distribution, with the possibility to deliver high doses to the target volume while sparing surrounding tissue. Children receiving PBT for an intracranial tumor between August 2013 and October 2017 were enrolled in the prospective registry study KiProReg. Patient's clinical data including treatment, outcome, and follow-up were analyzed using descriptive statistics, Kaplan-Meier, and Cox regression analysis. Adverse events were scored according to the Common Terminology Criteria for Adverse Events (CTCAE) 4.0 before, during, and after PBT. Written reports of follow-up imaging were screened for newly emerged evidence of imaging changes, according to a list of predefined keywords for the first 14 months after PBT. Two hundred and ninety-four patients were enrolled in this study. The 3-year overall survival of the whole cohort was 82.7%, 3-year progression-free survival was 67.3%, and 3-year local control was 79.5%. Seventeen patients developed grade 3 adverse events of the CNS during long-term follow-up (new adverse event n = 7; deterioration n = 10). Two patients developed vision loss (CTCAE 4°). This analysis demonstrates good general outcomes after PBT.

Primary cilia contribute to the aggressiveness of atypical teratoid/rhabdoid tumors

Atypical teratoid/rhabdoid tumor (AT/RT) is a highly malignant brain tumor in infants that is characterized by loss of nuclear expression of SMARCB1 or SMARCA4 proteins. Recent studies show that AT/RTs comprise three molecular subgroups, namely AT/RT-TYR, AT/RT-MYC and AT/RT-SHH. The subgroups show distinct expression patterns of genes involved in ciliogenesis, however, little is known about the functional roles of primary cilia in the biology of AT/RT. Here, we show that primary cilia are present across all AT/RT subgroups with specific enrichment in AT/RT-TYR patient samples. Furthermore, we demonstrate that primary ciliogenesis contributes to AT/RT biology in vitro and in vivo. Specifically, we observed a significant decrease in proliferation and clonogenicity following disruption of primary ciliogenesis in AT/RT cell line models. Additionally, apoptosis was significantly increased via the induction of STAT1 and DR5 signaling, as detected by proteogenomic profiling. In a Drosophila model of SMARCB1 deficiency, concomitant knockdown of several cilia-associated genes resulted in a substantial shift of the lethal phenotype with more than 20% of flies reaching adulthood. We also found significantly extended survival in an orthotopic xenograft mouse model of AT/RT upon disruption of primary ciliogenesis. Taken together, our findings indicate that primary ciliogenesis or its downstream signaling contributes to the aggressiveness of AT/RT and, therefore, may constitute a novel therapeutic target.

Iatrogenic Influence on Prognosis of Radiation-Induced Contrast Enhancements in Patients with Glioma WHO 1-3 following Photon and Proton Radiotherapy

BACKGROUND AND PURPOSE

Radiation-induced contrast enhancement (RICE) is a common side effect following radiotherapy for glioma, but both diagnosis and handling are challenging. Due to the potential risks associated with RICE and its challenges in differentiating RICE from tumor progression, it is critical to better understand how RICE prognosis depends on iatrogenic influence.

MATERIALS AND METHODS

We identified 99 patients diagnosed with RICE who were previously treated with either photon or proton therapy for World Health Organization (WHO) grade 1-3 primary gliomas. Post-treatment brain MRI-based volumetric analysis and clinical data collection was performed at multiple time points.

RESULTS

The most common histologic subtypes were astrocytoma (50%) and oligodendroglioma (46%). In 67%, it was graded WHO grade 2 and in 86% an IDH mutation was present. RICE first occurred after 16 months (range: 1 - 160) in median. At initial RICE occurrence, 39% were misinterpreted as tumor progression. A tumor-specific therapy including chemotherapy or re-irradiation led to a RICE size progression in 86% and 92% of cases, respectively and RICE symptom progression in 57% and 65% of cases, respectively. A RICE-specific therapy such as corticosteroids or Bevacizumab for larger or symptomatic RICE led to a RICE size regression in 81% of cases with symptom stability or regression in 62% of cases.

CONCLUSIONS

While with chemotherapy and re-irradiation a RICE progression was frequently observed, anti-edematous or anti-VEGF treatment frequently went along with a RICE regression. For RICE, correct diagnosis and treatment decisions are challenging and critical and should be made interdisciplinarily.

Brainstem Toxicity in Pediatric Patients Treated with Protons Using a Single-vault Synchrocyclotron System

Purpose

Cranial radiation therapy remains an integral component of curative treatment for pediatric patients with brain tumors. Proton beam radiation therapy (PBT) can limit collateral radiation dose to surrounding normal tissue, thus reducing off-target exposure while maintaining appropriate tumor coverage. While PBT offers significant advantages over photon therapy for pediatric patients with intracranial malignancies, cases of brainstem necrosis after PBT have raised concerns that PBT may pose an increased risk of necrosis over photon therapy. We investigated the incidence of brainstem necrosis at our institution in children treated with PBT for intracranial malignancies.

Patients and Methods

Patients with pediatric brain tumor treated with passively scattered PBT, using a gantry-mounted, synchrocyclotron single-vault system between 2013 and 2018, were retrospectively reviewed. Inclusion criteria included patients 21 years of age or younger who received a minimum 0.1 cm³ maximum brainstem dose of 50 Gray relative biological effectiveness (GyRBE). Patients were assessed for “central nervous system necrosis” in the brainstem per the Common Terminology Criteria for Adverse Events (CTCAE), version 5.0 (US National Cancer Institute, Bethesda, Maryland) criteria.

Results

Fifty-eight patients were included for analysis. The median age was 10.3 years. Twenty-one (36.2%) patients received craniospinal irradiation. Thirty-four (58.6%) patients received chemotherapy. The median prescription radiation dose was 54 GyRBE. Regarding published dosimetric constraints used at 3 separate proton centers, the goal brainstem D50% <52 GyRBE was exceeded in 23 (40%) patients, but the brainstem Dmax <58 GyRBE was not exceeded in any patients. No patient experienced grade ≥2 brainstem injury. One patient demonstrated radiographic changes consistent with grade 1 toxicity. This patient had myeloablative chemotherapy with tandem stem cell rescue before PBT.

Conclusion

Our data demonstrates a low risk of any brainstem injury in children treated with passively scattered PBT using a single-vault synchrocyclotron.

Molecular targeted therapies for pediatric atypical teratoid/rhabdoid tumors

Atypical teratoid/rhabdoid tumors (AT/RTs) are lethal central nervous system tumors, which are primarily diagnosed in infants. Current treatments for AT/RTs include surgery, radiotherapy, and chemotherapy; these treatments have poor prognoses and challenging side effects. The pivotal genetic event in AT/RT pathogenesis comprises the inactivation of SMARCB1 or SMARCA4. Recent epigenetic studies have demonstrated mutual and subtype-specific epigenetic derangements that drive tumorigenesis; the exploitation of these potential targets might improve the dismal treatment outcomes of AT/RTs. This review aims to summarize the literature concerning targeted molecular therapies for pediatric AT/RTs.

Radiation-induced contrast enhancement following proton radiotherapy for low-grade glioma depends on tumor characteristics and is rarer in children than adults

BACKGROUND AND PURPOSE

Proton beam radiotherapy (PRT) is used in the treatment of low-grade glioma (LGG) to mitigate long-term sequelae. Following PRT, increased rates of radiation-induced contrast enhancements (RICE) are suspected but poorly understood.

MATERIALS AND METHODS

We analyzed consecutive 227 patients (42 children and 185 adults) treated with PRT (54Gy RBE) for LGG from 2010 to 2020 and followed with serial clinical exams and magnetic resonance imaging for in median 5.6 years.

RESULTS

Tumors were graded WHO 1 in a minority (n = 22, 12%) of adults, but a majority of children (n = 29, 69%). In contrast, tumors were graded WHO 2 in the majority (n = 160, 87%) of adults and a minority of children (n = 10, 24%). Five-year overall survival following PRT was 81% in adults and 91% in children. The risk of RICE was 5-fold more frequent in adults (25%) versus children (5%) (p = 0.0043). In children and adults, RICE were symptomatic in 50% and 55% (n=1 and 26) of cases with CTCAE grade 0 in 47% (n=23), grade 1 in 25% (n=12), 0% grade 2 (n=0) and 29% grade 3 (n=14), respectively. In adults, RICE risk was associated to WHO grading (8% in WHO grade 1 vs. 24% in WHO grade 2, p = 0.026), independent of age (p=0.44) and irradiation dose (p=0.005), but not independent of IDH mutational status.

CONCLUSIONS

These data demonstrate effectiveness of PRT for LGG in both children and adults. The RICE risk is lower in children which are a main target group for PRT and differs with WHO grading.

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.

MR Imaging of Pediatric Brain Tumors

Primary brain tumors are the most common solid neoplasms in children and a leading cause of mortality in this population. MRI plays a central role in the diagnosis, characterization, treatment planning, and disease surveillance of intracranial tumors. The purpose of this review is to provide an overview of imaging methodology, including conventional and advanced MRI techniques, and illustrate the MRI appearances of common pediatric brain tumors.

A roadmap to clinical trials for FLASH

While FLASH radiation therapy is inspiring enthusiasm to transform the field, it is neither new nor well understood with respect to the radiobiological mechanisms. As FLASH clinical trials are designed, it will be important to ensure we can deliver dose consistently and safely to every patient. Much like hyperthermia and proton therapy, FLASH is a promising new technology that will be complex to implement in the clinic and similarly will require customized credentialing for multi‐institutional clinical trials. There is no doubt that FLASH seems promising, but many technologies that we take for granted in conventional radiation oncology, such as rigorous dosimetry, 3D treatment planning, volumetric image guidance, or motion management, may play a major role in defining how to use, or whether to use, FLASH radiotherapy. Given the extended time frame for patients to experience late effects, we recommend moving deliberately but cautiously forward toward clinical trials. In this paper, we review the state of quality assurance and safety systems in FLASH, identify critical pre‐clinical data points that need to be defined, and suggest how lessons learned from previous technological advancements will help us close the gaps and build a successful path to evidence‐driven FLASH implementation.

Quantifying the risk and dosimetric variables of symptomatic brainstem injury after proton beam radiation in pediatric brain tumors

BACKGROUND

Brainstem toxicity after radiation therapy (RT) is a devastating complication and a particular concern with proton radiation (PBT). We investigated the incidence and clinical correlates of brainstem injury in pediatric brain tumors treated with PBT.

METHODS

All patients <21 years with brain tumors treated with PBT at our institution from 2007-2019, with a brainstem Dmean >30 Gy and/or Dmax >50.4 Gy were included. Symptomatic brainstem injury (SBI) was defined as any new or progressive cranial neuropathy, ataxia, and/or motor weakness with corresponding radiographic abnormality within brainstem.

RESULTS

A total of 595 patients were reviewed and 468 (medulloblastoma = 200, gliomas = 114, ependymoma = 87, ATRT = 43) met our inclusion criteria. Median age at RT was 6.3 years and median prescribed RT dose was 54Gy [RBE]. Fifteen patients (3.2%) developed SBI, at a median of 4 months after RT. Grades 2, 3, 4, and 5 brainstem injuries were seen in 7, 5, 1, and 2 patients respectively. Asymptomatic radiographic changes were seen in 51 patients (10.9%). SBI was significantly higher in patients with age ≤3 years, female gender, ATRT histology, patients receiving high-dose chemotherapy with stem cell rescue, and those not receiving craniospinal irradiation. Patients with SBI had a significantly higher V50-52. In 2014, our institution started using strict brainstem dose constraints (Dmax ≤57 Gy, Dmean ≤52.4 Gy, and V54≤10%). There was a trend towards decrease in SBI from 4.4% (2007-2013) to 1.5% (2014-2019) (P = .089) without affecting survival.

CONCLUSION

Our results suggest a low risk of SBI after PBT for pediatric brain tumors, comparable to photon therapy. A lower risk was seen after adopting strict brainstem dose constraints.

Pretreatment Normal WM Magnetization Transfer Ratio Predicts Risk of Radiation Necrosis in Patients with Medulloblastoma

BACKGROUND AND PURPOSE

Radiation necrosis, for which abnormal WM enhancement is a hallmark, is an uncommon complication of craniospinal irradiation in children with medulloblastoma. The magnetization transfer ratio measures macromolecular content, dominated by myelin in the WM. We investigated whether the pretreatment supratentorial (nonsurgical) WM magnetization transfer ratio could predict patients at risk for radiation necrosis after radiation therapy for medulloblastoma.

MATERIALS AND METHODS

Ninety-five eligible patients with medulloblastoma (41% female; mean age, 11.0 [SD, 5.4]  years) had baseline balanced steady-state free precession MR imaging before proton or photon radiation therapy. Associations among baseline supratentorial magnetization transfer ratio, radiation necrosis (spontaneously resolving/improving parenchymal enhancement within the radiation field)³, age, and the presence of visible brain metastases were explored by logistic regression and parametric/nonparametric techniques as appropriate.

RESULTS

Twenty-three of 95 (24.2%) children (44% female; mean age, 10.7 [SD, 6.7] years) developed radiation necrosis after radiation therapy (19 infratentorial, 1 supratentorial, 3 both). The mean pretreatment supratentorial WM magnetization transfer ratio was significantly lower in these children (43.18 versus 43.50, P = .03). There was no association between the supratentorial WM magnetization transfer ratio and age, sex, risk/treatment stratum, or the presence of visible brain metastases.

CONCLUSIONS

A lower baseline supratentorial WM magnetization transfer ratio may indicate underlying structural WM susceptibility to radiation necrosis and may identify children at risk for developing radiation necrosis after craniospinal irradiation for medulloblastoma.

Mechanisms and Review of Clinical Evidence of Variations in Relative Biological Effectiveness in Proton Therapy

Proton therapy is increasingly being used as a radiation therapy modality. There is uncertainty about the biological effectiveness of protons relative to photon therapies as it depends on several physical and biological parameters. Radiation oncology currently applies a constant and generic value for the relative biological effectiveness (RBE) of 1.1, which was chosen conservatively to ensure tumor coverage. The use of a constant value has been challenged particularly when considering normal tissue constraints. Potential variations in RBE have been assessed in several published reviews but have mostly focused on data from clonogenic cell survival experiments with unclear relevance for clinical proton therapy. The goal of this review is to put in vitro findings in relation to clinical observations. Relevant in vivo pathways determining RBE for tumors and normal tissues are outlined, including not only damage to tumor cells and parenchyma but also vascular damage and immune response. Furthermore, the current clinical evidence of varying RBE is reviewed. The assessment can serve as guidance for treatment planning, personalized dose prescriptions, and outcome analysis.

Proton Minibeam Radiation Therapy and Arc Therapy: Proof of Concept of a Winning Alliance

Simple Summary

Normal tissue’s morbidity continues to limit the increase in the therapeutic index in radiation therapy. This study explores the potential advantages of combining proton arc therapy and proton minibeam radiation therapy, which have already individually shown a significant normal tissue’s sparing. This alliance aims to integrate the benefits of those techniques in a single approach.

Abstract

(1) Background: Proton Arc Therapy and Proton Minibeam Radiation Therapy are two novel therapeutic approaches with the potential to lower the normal tissue complication probability, widening the therapeutic window for radioresistant tumors. While the benefits of both modalities have been individually evaluated, their combination and its potential advantages are being assessed in this proof-of-concept study for the first time. (2) Methods: Monte Carlo simulations were employed to evaluate the dose and LET distributions in brain tumor irradiations. (3) Results: a net reduction in the dose to normal tissues (up to 90%), and the preservation of the spatial fractionation of the dose were achieved for all configurations evaluated. Additionally, Proton Minibeam Arc Therapy (pMBAT) reduces the volumes exposed to high-dose and high-LET values at expense of increased low-dose and intermediate-LET values. (4) Conclusions: pMBAT enhances the individual benefits of proton minibeams while keeping those of conventional proton arc therapy. These results might facilitate the path towards patients’ treatments since lower peak doses in normal tissues would be needed than in the case of a single array of proton minibeams.

Longitudinal Changes in Brain Diffusion MRI Indices during and after Proton Beam Therapy in a Child with Pilocytic Astrocytoma: A Case Report

Proton beam therapy (PBT) is an effective pediatric brain tumor treatment. However, the resulting microstructural changes within and around irradiated tumors are unknown. We retrospectively applied diffusion tensor imaging (DTI) and free-water imaging (FWI) on diffusion-weighted magnetic resonance imaging (dMRI) data to monitor microstructural changes during the PBT and after 8 months in a pilocytic astrocytoma (PA) and normal-appearing white matter (NAWM). We evaluated the conventional MRI- and dMRI-derived indices from six MRI sessions (t0–t5) in a Caucasian child with a hypothalamic PA: at baseline (t0), during the PBT (t1–t4) and after 8 months (t5). The tumor voxels were classified as “solid” or “fluid” based on the FWI. While the tumor volume remained stable during the PBT, the dMRI analyses identified two different response patterns: (i) an increase in fluid content and diffusivity with anisotropy reductions in the solid voxels at t1, followed by (ii) smaller variations in fluid content but higher anisotropy in the solid voxels at t2–t4. At follow-up (t5), the tumor volume, fluid content, and diffusivity in the solid voxels increased. The NAWM showed dose-dependent microstructural changes. The use of the dMRI and FWI showed complex dynamic microstructural changes in the irradiated mass during the PBT and at follow-up, opening new avenues in our understanding of radiation-induced pathophysiologic mechanisms in tumors and the surrounding tissues.

Proton reirradiation for recurrent or new primary breast cancer in the setting of prior breast irradiation

BACKGROUND AND PURPOSE

Late local recurrences and second primary breast cancers are increasingly common. Proton beam therapy (PBT) reirradiation (reRT) may allow safer delivery of a second definitive radiotherapy (RT) course. We analyzed outcomes of patients with recurrent or new primary breast cancer who underwent reRT.

MATERIALS AND METHODS

In an IRB-approved retrospective study, patient/tumor characteristics, treatment parameters, outcomes, and toxicities were collected for all consecutive patients with recurrent or new primary non-metastatic breast cancer previously treated with breast or chest wall RT who underwent PBT reRT.

RESULTS

Forty-six patients received reRT using uniform (70%) or pencil beam (30%) scanning PBT. Median first RT, reRT, and cumulative doses were 60 Gy (range 45-66 Gy), 50.4 Gy(RBE) (40-66.6 Gy(RBE)), and 110 Gy(RBE) (96.6-169.4 Gy(RBE)), respectively. Median follow-up was 21 months. There were no local or regional recurrences; 17% developed distant recurrence. Two-year DMFS and OS were 92.0% and 93.6%, respectively. Nine of 13 (69.2%) patients who underwent implant or flap reconstruction developed capsular contracture, 3 (23.1%) requiring surgical intervention. One (7.7%) patient developed grade 3 breast pain requiring mastectomy after breast conserving surgery. No acute or late grade 4-5 toxicities were seen. Increased body mass index (BMI) was protective of grade ≥ 2 acute toxicity (OR = 0.84, 95%CI = 0.70-1.00).

CONCLUSION

In the largest series to date of PBT reRT for breast cancer recurrence or new primary after prior definitive breast or chest wall RT, excellent locoregional control and few high-grade toxicities were encountered. PBT reRT may provide a relatively safe and highly effective salvage option. Additional patients and follow-up are needed to correlate composite normal tissue doses with toxicities and assess long-term outcomes.

Postsurgical geometrical variations of tumor bed and brainstem during photon and proton therapy for pediatric tumors of the posterior fossa: dosimetric impact and predictive factors

PURPOSE

Brainstem radionecrosis is an important issue during the irradiation of tumors of the posterior fossa. The aim of the present study is to analyze postsurgical geometrical variations of tumor bed (TB) and brainstem (BS) and their impact on dosimetry.

METHODS

Retrospective collection of data from pediatric patients treated at a single institution. Availability of presurgical magnetic resonance imaging (MRI) was verified; availability of at least two postsurgical MRIs was considered a further inclusion criterion. The following metrics were analyzed: total volume, Dice similarity coefficient (DSC), and Haudsdorff distances (HD).

RESULTS

Fourteen patients were available for the quantification of major postsurgical geometrical variations of TB. DSC, HD max, and HD average values were 0.47 (range: 0.08;0.76), 11.3 mm (7.7;24.5), and 2.6 mm (0.7;6.7) between the first and the second postoperative MRI, respectively. Postsurgical geometrical variations of the BS were also observed. Coverage to the TB was reduced in one patient (D95: -2.9 Gy), while D2 to the BS was increased for the majority of patients. Overall, predictive factors for significant geometrical changes were presurgical gross tumor volume (GTV) > 33 mL, hydrocephaly at diagnosis, Luschka foramen involvement, and younger age (≤ 8 years).

CONCLUSION

Major volume changes were observed in this cohort, with some dosimetric impact. The use of a recent co-registration MRI is advised. The 2-3 mm HD average observed should be considered in the planning target volume/planning organ at risk volume (PTV/PRV) margin and/or robust optimization planning. Results from wider efforts are needed to verify our findings.

Brain network hubs and cognitive performance of survivors of childhood infratentorial tumors

BACKGROUND

Childhood infratentorial tumor patients frequently suffer from long-term cognitive deficits. As each constituent of their treatment can lead to neurotoxicity, cascade effects can lead to profound reorganization of the underlying brain network, the so-called 'connectome'. However, to date, few studies have assessed the relationship between brain network topology, the functional role of network hubs (i.e. highly connected regions), and neurocognitive outcomes in adult survivors of childhood infratentorial tumors.

METHODS

In this cross-sectional study, childhood infratentorial tumor survivors (n = 21: pilocytic astrocytoma (n = 8), ependymoma (n = 1) and medulloblastoma (n = 12)) and healthy controls (n = 21) were recruited. Using multishell diffusion-weighted MRI, microstructural organization and topology of supratentorial white matter was investigated; using a voxel-based approach, a fixel-based analysis, and a graph theoretical approach. In addition, neurocognitive subscales of the WAIS-IV intelligence test, and their relationship with nodal strength and network efficiency metrics were assessed.

RESULTS

Similar to earlier studies, we observed widespread decreases in fractional anisotropy (FA) in patients compared to controls, based on voxel-based analyses. In addition, the fixel-based analyses dissociated macro- from microstructural changes, which were encountered in in infratentorial versus supratentorial brain areas, respectively. Finally, regional reorganization (i.e. differences in local efficiency) occurred mainly in hubs, which suggests a specific vulnerability of these areas. These hubs were not only mostly affected, but also most strongly correlated with the intelligence subscales.

CONCLUSION

This study suggests that network hubs are functionally important for intellectual outcomes in infratentorial tumor survivors. Furthermore, these regions could be the primary targets of treatment toxicity. Validation of this specific hypothesis in larger samples is required.

Normal Tissue Injury Induced by Photon and Proton Therapies: Gaps and Opportunities

Despite technological advances in radiation therapy (RT) and cancer treatment, patients still experience adverse effects. Proton therapy (PT) has emerged as a valuable RT modality that can improve treatment outcomes. Normal tissue injury is an important determinant of the outcome; therefore, for this review, we analyzed 2 databases: (1) clinical trials registered with ClinicalTrials.gov and (2) the literature on PT in PubMed, which shows a steady increase in the number of publications. Most studies in PT registered with ClinicalTrials.gov with results available are nonrandomized early phase studies with a relatively small number of patients enrolled. From the larger database of nonrandomized trials, we listed adverse events in specific organs/sites among patients with cancer who are treated with photons and protons to identify critical issues. The present data demonstrate dosimetric advantages of PT with favorable toxicity profiles and form the basis for comparative randomized prospective trials. A comparative analysis of 3 recently completed randomized trials for normal tissue toxicities suggests that for early stage non-small cell lung cancer, no meaningful comparison could be made between stereotactic body RT and stereotactic body PT due to low accrual (NCT01511081). In addition, for locally advanced non-small cell lung cancer, a comparison of intensity modulated RTwith passive scattering PT (now largely replaced by spot-scanned intensity modulated PT), PT did not provide any benefit in normal tissue toxicity or locoregional failure over photon therapy. Finally, for locally advanced esophageal cancer, proton beam therapy provided a lower total toxicity burden but did not improve progression-free survival and quality of life (NCT01512589). The purpose of this review is to inform the limitations of current trials looking at protons and photons, considering that advances in technology, physics, and biology are a continuum, and to advocate for future trials geared toward accurate precision RT that need to be viewed as an iterative process in a defined path toward delivering optimal radiation treatment. A foundational understanding of the radiobiologic differences between protons and photons in tumor and normal tissue responses is fundamental to, and necessary for, determining the suitability of a given type of biologically optimized RT to a patient or cohort.

What can space radiation protection learn from radiation oncology?

Protection from cosmic radiation of crews of long-term space missions is now becoming an urgent requirement to allow a safe colonization of the moon and Mars. Epidemiology provides little help to quantify the risk, because the astronaut group is small and as yet mostly involved in low-Earth orbit mission, whilst the usual cohorts used for radiation protection on Earth (e.g. atomic bomb survivors) were exposed to a radiation quality substantially different from the energetic charged particle field found in space. However, there are over 260,000 patients treated with accelerated protons or heavier ions for different types of cancer, and this cohort may be useful for quantifying the effects of space-like radiation in humans. Space radiation protection and particle therapy research also share the same tools and devices, such as accelerators and detectors, as well as several research topics, from nuclear fragmentation cross sections to the radiobiology of densely ionizing radiation. The transfer of the information from the cancer radiotherapy field to space is manifestly complicated, yet the two field should strengthen their relationship and exchange methods and data.