Pseudoprogression after radiation therapies for low grade glioma in children and adults: A systematic review and meta-analysis

Case report: Pediatric low-grade gliomas: a fine balance between treatment options, timing of therapy, symptom management and quality of life

Introduction

Pediatric low-grade gliomas (pLGG) are the most common brain tumor in children and encompass a wide range of histologies. Treatment may pose challenges, especially in those incompletely resected or those with multiple recurrence or progression.

Case description

We report the clinical course of a girl diagnosed with pilocytic astrocytoma and profound hydrocephalus at age 12 years treated with subtotal resection, vinblastine chemotherapy, and focal proton radiotherapy. After radiotherapy the tumor increased in enhancement temporarily with subsequent resolution consistent with pseudoprogression. Despite improvement in imaging and radiographic local control, the patient continues to have challenges with headaches, visual and auditory concerns, stroke-like symptoms, and poor quality of life.

Conclusion

pLGG have excellent long-term survival; thus, treatments should focus on maintaining disease control and limiting long-term toxicities. Various treatment options exist including surgery, chemotherapy, targeted agents, and radiation therapy. Given the morbidity associated with pLGG, individualized treatment approaches are necessary, with a multi-disciplinary approach to care focused on minimizing treatment side effects, and promoting optimal quality of life for patients.

Resistance, rebound, and recurrence regrowth patterns in pediatric low-grade glioma treated by MAPK inhibition: A modified Delphi approach to build international consensus-based definitions-International Pediatric Low-Grade Glioma Coalition

Pediatric low-grade glioma (pLGG) is the most common childhood brain tumor group. The natural history, when curative resection is not possible, is one of a chronic disease with periods of tumor stability and episodes of tumor progression. While there is a high overall survival rate, many patients experience significant and potentially lifelong morbidities. The majority of pLGGs have an underlying activation of the RAS/MAPK pathway due to mutational events, leading to the use of molecularly targeted therapies in clinical trials, with recent regulatory approval for the combination of BRAF and MEK inhibition for BRAFV600E mutated pLGG. Despite encouraging activity, tumor regrowth can occur during therapy due to drug resistance, off treatment as tumor recurrence, or as reported in some patients as a rapid rebound growth within 3 months of discontinuing targeted therapy. Definitions of these patterns of regrowth have not been well described in pLGG. For this reason, the International Pediatric Low-Grade Glioma Coalition, a global group of physicians and scientists, formed the Resistance, Rebound, and Recurrence (R3) working group to study resistance, rebound, and recurrence. A modified Delphi approach was undertaken to produce consensus-based definitions and recommendations for regrowth patterns in pLGG with specific reference to targeted therapies.

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.

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.

Pseudoprogression of thoracic tumor after radiotherapy in the era of immunotherapy: a case series

Pseudoprogression is rarely mentioned after radiotherapy except for central nervous system tumors. With the widespread of immunotherapy, the incidence of pseudoprogression of thoracic tumor after radiotherapy is increasing. This study summarized the clinical features of pseudoprogression in 4 patients who had underwent thoracic radiotherapy after and/or followed by immunotherapy. All of them had received chemotherapy and immunotherapy before thoracic radiotherapy. After radiotherapy, pseudoprogression occurred within 3 months after initiation of immune consolidation/rechallenge therapy. At least a 20% increase in the sum of the longest diameter of target lesions were measured on their chest image. During this period, patients' ECOG PS scores remained stable, specific serum tumor markers did not increase significantly. Treatment strategies did not change after pseudoprogression. The causes of radiographic pseudoprogression in this case series may be attributed to disturbances such as pneumonitis, atelectasis, mucus blockages and infection. In the era of immunotherapy, pseudoprogression of thoracic tumors after chest radiotherapy might become a common phenomenon. It is important for us to identify pseudoprogression based on patient's general status, radiological changes, and laboratory tests.

Incidence and characteristics of pseudoprogression in IDH-mutant high-grade gliomas: A POLA network study

BACKGROUND

Incidence and characteristics of pseudoprogression in isocitrate dehydrogenase-mutant high-grade gliomas (IDHmt HGG) remain to be specifically described.

METHODS

We analyzed pseudoprogression characteristics and explored the possibility of pseudoprogression misdiagnosis in IDHmt HGG patients, treated with radiotherapy (RT) (with or without chemotherapy [CT]), included in the French POLA network. Pseudoprogression was analyzed in patients with MRI available for review (reference cohort, n = 200). Pseudoprogression misdiagnosis was estimated in this cohort and in an independent cohort (control cohort, n = 543) based on progression-free survival before and after first progression.

RESULTS

In the reference cohort, 38 patients (19%) presented a pseudoprogression after a median time of 10.5 months after RT. Pseudoprogression characteristics were similar across IDHmt HGG subtypes. In most patients, it consisted of the appearance of one or several infracentimetric, asymptomatic, contrast-enhanced lesions occurring within 2 years after RT. The only factor associated with pseudoprogression occurrence was adjuvant PCV CT. Among patients considered as having a first true progression, 7 out of 41 (17%) in the reference cohort and 35 out of 203 (17%) in the control cohort were retrospectively suspected to have a misdiagnosed pseudoprogression. Patients with a misdiagnosed pseudoprogression were characterized by a time to event and an outcome similar to that of patients with a pseudoprogression but presented with larger and more symptomatic lesions.

CONCLUSION

In patients with an IDHmt HGG, pseudoprogression occurs later than in IDH-wildtype glioblastomas and seems not only frequent but also frequently misdiagnosed. Within the first 2 years after RT, the possibility of a pseudoprogression should be carefully considered.

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.

Linear Energy Transfer and Relative Biological Effectiveness Investigation of Various Structures for a Cohort of Proton Patients With Brain Tumors

Purpose

The current knowledge on biological effects associated with proton therapy is limited. Therefore, we investigated the distributions of dose, dose-averaged linear energy transfer (LET_d), and the product between dose and LET_d (DLET_d) for a patient cohort treated with proton therapy. Different treatment planning system features and visualization tools were explored.

Methods and Materials

For a cohort of 24 patients with brain tumors, the LET_d, DLET_d, and dose was calculated for a fixed relative biological effectiveness value and 2 variable models: plan-based and phenomenological. Dose threshold levels of 0, 5, and 20 Gy were imposed for LET_d visualization. The relationship between physical dose and LET_d and the frequency of LET_d hotspots were investigated.

Results

The phenomenological relative biological effectiveness model presented consistently higher dose values. For lower dose thresholds, the LET_d distribution was steered toward higher values related to low treatment doses. Differences up to 26.0% were found according to the threshold. Maximum LET_d values were identified in the brain, periventricular space, and ventricles. An inverse relationship between LET_d and dose was observed. Frequency information to the domain of dose and LET_d allowed for the identification of clusters, which steer the mean LET_d values, and the identification of higher, but sparse, LET_d values.

Conclusions

Identifying, quantifying, and recording LET distributions in a standardized fashion is necessary, because concern exists over a link between toxicity and LET hotspots. Visualizing DLET_d or dose × LET_d during treatment planning could allow for clinicians to make informed decisions.

Diffusion imaging could aid to differentiate between glioma progression and treatment-related abnormalities: a meta-analysis

Background

In a considerable subgroup of glioma patients treated with (chemo) radiation new lesions develop either representing tumor progression (TP) or treatment-related abnormalities (TRA). Quantitative diffusion imaging metrics such as the Apparent Diffusion Coefficient (ADC) and Fractional Anisotropy (FA) have been reported as potential metrics to noninvasively differentiate between these two phenomena. Variability in performance scores of these metrics and absence of a critical overview of the literature contribute to the lack of clinical implementation. This meta-analysis therefore critically reviewed the literature and meta-analyzed the performance scores.

Methods

Systematic searching was carried out in PubMed, EMBASE and The Cochrane Library. Using predefined criteria, papers were reviewed. Diagnostic accuracy values of suitable papers were meta-analyzed quantitatively.

Results

Of 1252 identified papers, 10 ADC papers, totaling 414 patients, and 4 FA papers, with 154 patients were eligible for meta-analysis. Mean ADC values of the patients in the TP/TRA groups were 1.13 × 10⁻³mm²/s (95% CI 0.912 × 10^–3–1.32 × 10⁻³mm²/s) and 1.38 × 10⁻³mm²/s (95% CI 1.33 × 10^–3–1.45 × 10⁻³mm²/s, respectively. Mean FA values of TP/TRA was 0.19 (95% CI 0.189–0.194) and 0.14 (95% CI 0.137–0.143) respectively. A significant mean difference between ADC and FA values in TP versus TRA was observed (p = 0.005).

Conclusions

Quantitative ADC and FA values could be useful for distinguishing TP from TRA on a meta-level. Further studies using serial imaging of individual patients are warranted to determine the role of diffusion imaging in glioma patients.

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.

A systematic review of clinical studies on variable proton Relative Biological Effectiveness (RBE)

Recently, a number of clinical studies have explored links between possible Relative Biological Effectiveness (RBE) elevations and patient toxicities and/or image changes following proton therapy. Our objective was to perform a systematic review of such studies. We applied a "Problem [RBE], Intervention [Protons], Population [Patients], Outcome [Side effect]" search strategy to the PubMed database. From our search, we retrieved studies which: (a) performed novel voxel-wise analyses of patient effects versus physical dose and LET (n = 13), and (b) compared image changes between proton and photon cohorts with regard to proton RBE (n = 9). For each retrieved study, we extracted data regarding: primary tumour type; size of patient cohort; type of image change studied; image-registration method (deformable or rigid); LET calculation method, and statistical methodology. We compared and contrasted their methods in order to discuss the weight of clinical evidence for variable proton RBE. We concluded that clinical evidence for variable proton RBE remains statistically weak at present. Our principal recommendation is that proton centres and clinical trial teams collaborate to standardize follow-up protocols and statistical analysis methods, so that larger patient cohorts can ultimately be considered for RBE analyses.

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.

Regression and pseudoprogression of pediatric optic pathway glioma in patients treated with proton beam therapy

PURPOSE

We examined regression patterns in pediatric optic pathway gliomas (OPGs) after proton beam therapy (PBT) and evaluated local control and visual outcomes.

METHODS

A total of 42 brain magnetic resonance imaging (MRI) scans from seven consecutive sporadic OPGs that were initially treated with chemotherapy and received PBT between June 2007 and September 2016 at the National Cancer Center, Korea were analyzed. Patients underwent brain MRI regularly before and after PBT. Total tumor, cystic lesion, and solid enhancing lesion area delineation and volume calculations were performed on gadolinium-enhanced T1-weighted MRI using Eclipse version 13, Varian.

RESULTS

The median follow-up period after PBT was 70 months (range 47-88). The median age at the time of PBT was 7 years (range 4-16) and the median duration of chemotherapy before referral to PBT center was 25 months (range 3-70). The median time to the greatest increase in cystic volume was 32 months (range 12-43) after PBT. Solid enhancing lesion volume gradually decreased throughout the follow-up period. On an individual basis, total volume change was varied. However, on average, it regressed, although at a slower rate than solid enhancing lesion volume did. The local control rate was 85.7% (5-year progression-free survival rate, 80%; 5-year overall survival rate, 100%) and the rate of vision preservation was 71.4% (five of seven patients).

CONCLUSION

The regression patterns in pediatric OPGs after PBT involve significant cystic change. Therefore, total volume is not appropriate for evaluating response. Care by a multidisciplinary team is necessary to manage clinical symptoms related to radiologic changes.

Pseudoprogression is frequent following front-line radiotherapy in pediatric low-grade glioma - results from the German LGG cohort

PURPOSE

Expansion of MRI T2- and/or T1-tumor lesion volume after radiotherapy (RT) may indicate pseudoprogression (PsPD). The differentiation between true progression and PsPD is a clinical challenge and under-investigated in pediatric low-grade glioma (LGG). We evaluated radiological criteria for PsPD following front-line RT and investigated the frequency and duration of PsPD following three RT-modalities within the framework of the [Anonymized for Review] LGG-studies.

METHODS

Baseline and follow-up MRI-scans of 136 patients (72 [52.9%] male, median age at start of RT 11.3 years [range 0.8-25.9]) of the [Anonymized for Review] cohorts (¹²⁵iodine-interstitial RT [IS; n=51], photon-beam [XRT; n=60] or proton-beam RT [PBT; n=25]) were centrally evaluated for: Increasing 1) total tumor-associated T2-lesion, 2) focal tumor-associated T2-lesion and 3) contrast-enhancing tumor over a period of 24 months following RT. The pattern of these criteria initiated "suspicion" of PsPD, their evolution determined "definite" PsPD.

RESULTS

Definite PsPD was radiologically determined in 54/136 (39.7%) without differences in frequency between RT-modalities: IS 22/48 vs. XRT 24/54 vs. PBT 11/20; p=0.780. Definite PsPD occurred at median 6.3 months (IS 7.2 months; XRT 4.4 months; PBT 6.5 months) after RT-initiation and persisted for median 7.2 months (IS 8.5 months; XRT 7 months; PBT 7.4 months). Appearance of necrosis within the focal tumor-associated T2-lesion proved to be a relevant associated predictor of definite PsPD (p<0.001).

CONCLUSIONS

PsPD is frequent following irradiation of pediatric LGG and independent of the RT-modality (IS vs. XRT vs. PBT). Adequate identification of PsPD versus true progression is imperative to prevent unneeded salvage treatment.

Role of Mitochondria in Radiation Responses: Epigenetic, Metabolic, and Signaling Impacts

Until recently, radiation effects have been considered to be mainly due to nuclear DNA damage and their management by repair mechanisms. However, molecular biology studies reveal that the outcomes of exposures to ionizing radiation (IR) highly depend on activation and regulation through other molecular components of organelles that determine cell survival and proliferation capacities. As typical epigenetic-regulated organelles and central power stations of cells, mitochondria play an important pivotal role in those responses. They direct cellular metabolism, energy supply and homeostasis as well as radiation-induced signaling, cell death, and immunological responses. This review is focused on how energy, dose and quality of IR affect mitochondria-dependent epigenetic and functional control at the cellular and tissue level. Low-dose radiation effects on mitochondria appear to be associated with epigenetic and non-targeted effects involved in genomic instability and adaptive responses, whereas high-dose radiation effects (>1 Gy) concern therapeutic effects of radiation and long-term outcomes involving mitochondria-mediated innate and adaptive immune responses. Both effects depend on radiation quality. For example, the increased efficacy of high linear energy transfer particle radiotherapy, e.g., C-ion radiotherapy, relies on the reduction of anastasis, enhanced mitochondria-mediated apoptosis and immunogenic (antitumor) responses.

Proton Therapy and Gliomas: A Systematic Review

Background: Gliomas are primary cerebral tumors. Radiation therapy plays a key role in their treatment but with a risk of toxicity associated with the dose to and volume of normal tissue that is irradiated. With its precision properties allowing for the increased sparing of healthy tissue, proton therapy could be an interesting option for this pathology. Methods: Two reviewers performed a systematic review of original papers published between 2010 and July 2021 following PRISMA guidelines. We analyzed disease outcomes, toxicity outcomes, or dosimetry data in four separate groups: children/adults and individuals with low-/high-grade gliomas. Results: Among 15 studies, 11 concerned clinical and toxicity outcomes, and 4 reported dosimetry data. Proton therapy showed similar disease outcomes with greater tolerance than conventional radiation therapy, partly due to the better dosimetry plans. Conclusions: This review suggests that proton therapy is a promising technique for glioma treatment. However, studies with a high level of evidence are still needed to validate this finding.

Distinct imaging patterns of pseudoprogression in glioma patients following proton versus photon radiation therapy

PURPOSE

Criteria by the Radiologic Assessment in Neuro-Oncology (RANO) group outline the diagnosis of pseudoprogression (Ps) after photon therapy for gliomas based on timing and location. We noted that patients receiving proton therapy manifested radiographic changes that appear different than Ps after photon therapy, which could be interpreted as tumor progression. In this study, we retrospectively reviewed MR imaging after proton or photon radiation for gliomas. We propose criteria to characterize proton pseudoprogression (ProPs) as distinct from Ps seen after photons.

METHODS

Post-treatment MR imaging, clinical and pathological data of low grade glioma patients were reviewed. Overall, 57 patients receiving protons were reviewed for the presence of ProPs, and 43 patients receiving photons were reviewed for any equivalent imaging changes. Data collected included the location and timing of the new enhancement, tumor grade, molecular subtype, chemotherapy received, and clinical symptoms.

RESULTS

Fourteen patients (24.6%) had new enhancement following radiation therapy that was unique to treatment with protons. The mean time to development of the ProPs was 15.4 months (7-27 months). We established the following criteria to characterize ProPs: located at the distal end of the proton beam; resolves without tumor-directed therapy; and subjectively multifocal, patchy, and small (< 1 cm). In the group receiving photons, none had changes that met our criteria for ProPs.

CONCLUSION

Patients who receive protons have unique imaging changes after radiation therapy. ProPs could be mistaken for tumor progression, but typically resolves on follow up. Further studies are needed to understand the radiobiology and pathophysiology underlying these imaging changes.

Dynamic Susceptibility Perfusion Imaging for Differentiating Progressive Disease from Pseudoprogression in Diffuse Glioma Molecular Subtypes

Rationale and Objectives: Advanced adjuvant therapy of diffuse gliomas can result in equivocal findings in follow-up imaging. We aimed to assess the additional value of dynamic susceptibility perfusion imaging in the differentiation of progressive disease (PD) from pseudoprogression (PsP) in different molecular glioma subtypes. Materials and Methods: 89 patients with treated diffuse glioma with different molecular subtypes (IDH wild type (Astro-IDH^wt), IDH mutant astrocytomas (Astro-IDH^mut) and oligodendrogliomas), and tumor-suspect lesions on post-treatment follow-up imaging were classified into two outcome groups (PD or PsP) retrospectively by histopathology or clinical follow-up. The relative cerebral blood volume (rCBV) was assessed in the tumor-suspect FLAIR and contrast-enhancing (CE) lesions. We analyzed how a multilevel classification using a molecular subtype, the presence of a CE lesion, and two rCBV histogram parameters performed for PD prediction compared with a decision tree model (DTM) using additional rCBV parameters. Results: The PD rate was 69% in the whole cohort, 86% in Astro-IDH^wt, 52% in Astro-IDH^mut, and 55% in oligodendrogliomas. In the presence of a CE lesion, the PD rate was higher with 82%, 94%, 59%, and 88%, respectively; if there was no CE lesion, however, the PD rate was only 44%, 60%, 40%, and 33%, respectively. The additional use of the rCBV parameters in the DTM yielded a prediction accuracy for PD of 99%, 100%, 93%, and 95%, respectively. Conclusion: Utilizing combined information about the molecular tumor type, the presence or absence of CE lesions and rCBV parameters increases PD prediction accuracy in diffuse glioma.

Dihydrotanshinone I inhibits human glioma cell proliferation via the activation of ferroptosis

The aim of the present study was to investigate the effect of dihydrotanshinone I (DHI) on the survival of human glioma cells and the expression levels of ferroptosis-associated proteins. Human U251 and U87 glioma cells were cultured in vitro and treated with different concentrations of DHI and/or the ferroptosis inhibitor ferrostatin-1. A Cell Counting Kit-8 assay was used to determine the cell survival rate. The cells were further analyzed to determine their 5-, 12- and 15-hydroxyeicosatetraenoic acid (HETE), lactate dehydrogenase (LDH) and malondialdehyde (MDA) levels, and reduced glutathione (GSH)/oxidized glutathione (GSSG) ratios. Western blotting was used to detect ferroptosis-associated glutathione peroxidase 4 (GPX4) and long-chain acyl-CoA synthetase 4 (ACSL-4). Changes in the mitochondrial membrane potential (MMP) were also observed using tetramethylrhodamine methyl ester staining and confocal fluorescence microscopy. The results revealed that DHI inhibited the proliferation of human glioma cells. Following treatment of the U251 and U87 cells with DHI, changes in the expression levels of ferroptosis-associated proteins were observed; the expression level of GPX4 decreased and that of ACSL-4 increased. DHI also increased the levels of LDH and MDA in the human glioma cells and reduced the GSH/GSSG ratio. The DHI-treated cells also exhibited a marked reduction in MMP. Furthermore, ferrostatin-1 blocked the DHI-induced effects in human glioma cells. From these results, it may be concluded that DHI inhibits the proliferation of human glioma cells via the induction of ferroptosis.

Late Contrast Enhancing Brain Lesions in Proton-Treated Patients With Low-Grade Glioma: Clinical Evidence for Increased Periventricular Sensitivity and Variable RBE

PURPOSE

Late radiation-induced contrast-enhancing brain lesions (CEBLs) on magnetic resonance imaging (MRI) after proton therapy of brain tumors have been observed to occur frequently in regions of high linear energy transfer (LET) and in proximity to the ventricular system. We analyzed 110 patients with low-grade glioma treated with proton therapy to determine whether the risk for CEBLs is increased in proximity to the ventricular system and if there is a relationship between relative biological effectiveness (RBE) and LET.

METHODS AND MATERIALS

We contoured CEBLs identified on follow-up T1-MRI scans and computed dose and dose-averaged LET (LET_d) distributions for all patients using the Monte Carlo method. We then performed cross-validated voxel-level logistic regression to predict local risks for image change and to extract model parameters, such as the RBE. From the voxel-level model, we derived a model for patient-level risk prediction based on the treatment plan.

RESULTS

Of 110 patients, 23 exhibited 1 or several CEBLs on follow-up MRI scans. The voxel-level logistic model has an accuracy as follows: area under the curve of 0.94 and Brier score of 2.6 × 10^-5. Model predictions are a 3-fold increased risk in the 4 mm region around the ventricular system and an LET_d-dependent RBE of, for example, 1.20 for LET_d = 2 keV/μm and 1.50 for LET_d = 5 keV/μm. The patient-level risk model has an accuracy as follows: area under the curve of 0.78 and Brier score of 0.13.

CONCLUSIONS

Our findings present clinical evidence for an increased risk in ventricular proximity and for a proton RBE that increases significantly with increasing LET. We present a voxel-level model that accurately predicts the localization of late MRI contrast change and extrapolate a patient-level model that allows treatment plan-based risk prediction.