Association of 1p/19q Codeletion and Radiation Necrosis in Adult Cranial Gliomas After Proton or Photon Therapy

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.

Mixed effect model confirms increased risk of image changes with increasing linear energy transfer in proton therapy of gliomas

BACKGROUND AND PURPOSE

Radiation induced image changes (IC) on MRI have been observed after proton therapy for brain tumours. This study aims to create predictive models, with and without taking into account patient variation, based on dose, linear energy transfer (LET) and periventricular zone (PVZ) in a national cohort of patients with glioma treated with pencil beam scanning (PBS).

MATERIALS AND METHODS

A cohort of 87 consecutive patients with oligodendroglioma or astrocytoma (WHO grade 2-4) treated with PBS from January 2019 to December 2021 was included. All patients were treated with three to four beams. Monte Carlo calculations of dose and LET were performed for all treatment plans. Lesion weighted as well as mixed effect logistic regression models were developed to predict IC in a voxel.

RESULTS

12 patients (14 %) developed ICs on the follow-up MR-scans. Mixed effect modelling accounting for interpatient variation was justified by the non-negligible inter class correlation coefficient (ICC = 0.33). The two approaches identified similar model features and marginal improvement in model performance was found, when increasing model parameters from two (AUC = 0.92/0.94) to three (AUC = 0.93/0.95) parameters. Univariate analysis showed that patients treated with narrow beam configurations had an increased incidence of IC (p = 0.01).

CONCLUSION

14% of patients developed IC following PT. Lesion-weighted and mixed effect models resulted in similar model performance confirming increased risk of IC with increasing LET. The beam arrangement seems to influence the risk of IC and needs further investigation.

Unique brain injury patterns after proton vs photon radiotherapy for WHO grade 2-3 gliomas

BACKGROUND

Central nervous system (CNS) injury following brain-directed radiotherapy remains a major challenge. Proton radiotherapy (PRT) minimizes radiation to healthy brain, potentially limiting sequelae. We characterized CNS radiotoxicity, including radiation-induced leukoencephalopathy (RIL), brain tissue necrosis (TN), and cerebral microbleeds (CMB), in glioma patients treated with PRT or photons (XRT).

PATIENTS AND METHODS

Thirty-four patients (19 male; median age 39.6 years) with WHO grade 2-3 gliomas treated with partial cranial radiotherapy (XRT [n = 17] vs PRT[n = 17]) were identified and matched by demographic/clinical criteria. Radiotoxicity was assessed longitudinally for 3 years post-radiotherapy via serial analysis of T2/FLAIR- (for RIL), contrast-enhanced T1- (for TN), and susceptibility (for CMB)-weighted MRI sequences. RIL was rated at whole-brain and hemispheric levels using a novel Fazekas scale-informed scoring system.

RESULTS

The scoring system proved reliable (ICC > 0.85). Both groups developed moderate-to-severe RIL (62%[XRT]; 71%[PRT]) within 3 years; however, XRT was associated with persistent RIL increases in the contralesional hemisphere, whereas contralesional hemispheric RIL plateaued with PRT at 1-year post-radiotherapy (t = 2.180; P = .037). TN rates were greater with PRT (6%[XRT] vs 18%[PRT]; P = ns). CMB prevalence (76%[XRT]; 71%[PRT]) and burden (mean #CMB: 4.0[XRT]; 4.2[PRT]) were similar; however, XRT correlated with greater contralesional hemispheric CMB burden (27%[XRT]; 17%[PRT]; X2 = 4.986; P = .026), whereas PRT-specific CMB clustered at the radiation field margin (X2 = 14.7; P = .002).

CONCLUSIONS

CNS radiotoxicity is common and progressive in glioma patients. Injury patterns suggest radiation modality-specificity as RIL, TN, and CMB exhibit unique spatiotemporal differences following XRT vs PRT, likely reflecting underlying dosimetric and radiobiological differences. Familiarity with such injury patterns is essential to improve patient management. Prospective studies are needed to validate these findings and assess their impacts on neurocognitive function.

PROTON THERAPY FOR ADULT-TYPE DIFFUSE GLIOMA: A SYSTEMATIC REVIEW

BACKGROUND

We conducted a systematic review to evaluate outcomes and toxicities associated with proton therapy in the treatment of adult-type diffuse glioma.

METHODS

Following PRISMA guidelines, we searched PubMed for both prospective and retrospective studies on proton therapy for adult diffuse gliomas, including low-grade gliomas and glioblastomas. Survival and toxicity outcomes were reported separately for these glioma types.

RESULTS

Twelve studies from 2013 to 2023 were selected, comprising 3 prospective and 9 retrospective studies. The analysis covered 570 patients with low-grade gliomas and 240 patients with glioblastoma or WHO grade 4 gliomas. Proton therapy was found to be comparable to conventional radiotherapy in terms of survival outcomes. Its main advantage is the ability to minimize radiation exposure to healthy tissues.

DISCUSSION

Proton therapy offers comparable survival outcomes to conventional radiotherapy for adult diffuse gliomas and may enhance treatment tolerance, especially regarding neurocognitive function. A major limitation of this review is the predominance of retrospective studies. Future research should ensure rigorous patient selection and adhere to the latest WHO 2021 classification.

Early and late contrast enhancing lesions after photon radiotherapy for IDH mutated grade 2 diffuse glioma

OBJECTIVE

The interpretation of new enhancing lesions after radiotherapy for diffuse glioma remains a clinical challenge. We sought to characterize and classify new contrast enhancing lesions in a historical multicenter cohort of patients with IDH mutated grade 2 diffuse glioma treated with photon therapy.

METHODS

We reviewed all follow-up MRI's of all patients treated with radiotherapy for histologically confirmed, IDH mutated diffuse grade 2 glioma between 1-1-2007 and 31-12-2018 in two tertiary referral centers. Disease progression (PD) was defined in accordance with the RANO criteria for progressive disease in low grade glioma. Pseudoprogression (psPD) was defined as any transient contrast-enhancing lesion between the end of radiotherapy and PD, or any new contrast-enhancing lesion that remained stable over a period of 12 months in patients who did not exhibit PD.

RESULTS

A total of 860 MRI's of 106 patients were reviewed. psPD was identified in 24 patients (23%) on 76 MRI's. The cumulative incidence of psPD was 13% at 1 year, 22% at 5 years, and 28% at 10 years. The mean of the observed maximal volume of psPD was 2.4cc. The median Dmin in psPD lesions was 50.1 Gy. The presence of an 1p/19q codeletion was associated with an increased risk of psPD (subhazard ratio 2.34, p=0.048). psPD was asymptomatic in 83% of patients.

CONCLUSION

The cumulative incidence of psPD in grade 2 diffuse glioma increases over time. Consensus regarding event definition and statistical analysis is needed for comparisons between series investigating psPD.

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.

Radiation Therapy for IDH-Mutant Grade 2 and Grade 3 Diffuse Glioma: An ASTRO Clinical Practice Guideline

PURPOSE

This guideline provides evidence-based recommendations for adults with isocitrate dehydrogenase (IDH)-mutant grade 2 and grade 3 diffuse glioma, as classified in the 2021 World Health Organization (WHO) Classification of Tumours. It includes indications for radiation therapy (RT), advanced RT techniques, and clinical management of adverse effects.

METHODS

The American Society for Radiation Oncology convened a multidisciplinary task force to address 4 key questions focused on the RT management of patients with IDH-mutant grade 2 and grade 3 diffuse glioma. Recommendations were based on a systematic literature review and created using a predefined consensus-building methodology and system for grading evidence quality and recommendation strength.

RESULTS

A strong recommendation for close surveillance alone was made for patients with oligodendroglioma, IDH-mutant, 1p/19q codeleted, WHO grade 2 after gross total resection without high-risk features. For oligodendroglioma, WHO grade 2 with any high-risk features, adjuvant RT was conditionally recommended. However, adjuvant RT was strongly recommended for oligodendroglioma, WHO grade 3. A conditional recommendation for close surveillance alone was made for astrocytoma, IDH-mutant, WHO grade 2 after gross total resection without high-risk features. Adjuvant RT was conditionally recommended for astrocytoma, WHO grade 2, with any high-risk features and strongly recommended for astrocytoma, WHO grade 3. Dose recommendations varied based on histology and grade. Given known adverse long-term effects of RT, consideration for advanced techniques such as intensity modulated radiation therapy/volumetric modulated arc therapy or proton therapy were given as strong and conditional recommendations, respectively. Finally, based on expert opinion, the guideline recommends assessment, surveillance, and management for toxicity management.

CONCLUSIONS

Based on published data, the American Society for Radiation Oncology task force has proposed recommendations to inform the management of adults with IDH-mutant grade 2 and grade 3 diffuse glioma as defined by WHO 2021 classification, based on the highest quality published data, and best translated by our task force of subject matter experts.

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.

Quantitative study of the changes in brain white matter before and after radiotherapy by applying multi-sequence MR radiomics

Purpose

To analyse the changes in brain white matter before and after radiotherapy (RT) by applying multisequence MR radiomics features and to establish a relationship between the changes in radiomics features and radiation dose.

Methods

Eighty-eight patients with brain tumours who had undergone RT were selected in this study, and MR images (T1, T1+C, T2FLAIR, T2, DWI, and ASL) before and after RT were obtained. The brain white matter was delineated as an ROI under dose gradients of 0–5 Gy, 5–10 Gy, 10–15 Gy, 15–20 Gy, 20–30 Gy, 30–40 Gy, and 40–50 Gy. The radiomics features of each ROI were extracted, and the changes in radiomics features before and after RT for different sequences under different dose gradients were compared.

Results

At each dose gradient, statistically significant features of different MR sequences were mainly concentrated in three dose gradients, 5–10 Gy, 20–30 Gy, and 30–40 Gy. The T1+C sequence held the most features (66) under the 20–30 Gy dose gradient. There were 20 general features at dose gradients of 20–30 Gy, 30–40 Gy, and 40–50 Gy, and the changes in features first decreased and then increased following dose escalation. With dose gradients of 5–10 Gy and 10–15 Gy, only T1 and T2FLAIR had general features, and the rates of change were − 24.57% and − 29.32% for T1 and − 3.08% and − 10.87% for T2FLAIR, respectively. The changes showed an upward trend with increasing doses. For different MR sequences that were analysed under the same dose gradient, all sequences with 5–10 Gy, 20–30 Gy and 30–40 Gy had general features, except the T2FLAIR sequence, which was concentrated in the FirstOrder category feature, and the changes in features of T1 and T1+C were more significant than those of the other sequences.

Conclusions

MR radiomics features revealed microscopic changes in brain white matter before and after RT, although there was no constant dose-effect relationship for each feature. The changes in radiomics features in different sequences could reveal the radiation response of brain white matter to different doses.

Radiation induced contrast enhancement after proton beam therapy in patients with low grade glioma - How safe are protons?

PURPOSE

The optimal treatment strategy for low-grade glioma (LGG) is still a matter of controversy. Considering that the prognosis is typically favorable, the prevention of late sequelae is of particular importance. Proton beam therapy (PRT) has the potential to further reduce the burden of treatment related side effects. We set out to evaluate the clinical outcome of proton irradiation with a particular focus on morphologic features on magnetic resonance imaging (MRI).

METHODS

We assessed prospectively 110 patients who received radiotherapy with protons for histologically proven LGG. Clinical and radiological information were analyzed resulting in more than 1200 available MRI examinations with a median follow-up of 39 months. Newly diagnosed contrast-enhancing lesions on MRI were delineated and correlated with parameters of the corresponding treatment plan. A voxel-based dose-matched paired analysis of the linear energy transfer (LET) inside vs outside lesions was performed.

RESULTS

Proton beam irradiation of patients with low-grade glioma results in overall survival (OS) of 90% after seven years. Median progression free survival had not yet been reached with surviving fraction of 54% after seven years. The incidence of temporary or clinically silent radiation induced contrast enhancement was significantly higher than previously assumed, however, symptomatic radiation necrosis was only detected in one patient. These radiation-induced contrast-enhancing lesions were almost exclusively seen at the distal beam end of the proton beam. In 22 out of 23 patients, the average LET of voxels inside contrast-enhancing lesions was significantly increased, compared to dose-matched voxels outside the lesions.

CONCLUSION

Symptomatic radiation necrosis following PRT was as rare as conventional photon-based treatment series suggest. However, the increased incidence of asymptomatic radiation-induced brain injuries with an increased average LET observed in this cohort provides strong clinical evidence to support the hypothesis that the relative biological effectiveness of protons is variable and different to the fixed factor of 1.1 currently used worldwide.

Salvage therapies for radiation-relapsed isocitrate dehydrogenase-mutant astrocytoma and 1p/19q codeleted oligodendroglioma

Background

Optimal management for recurrent IDH-mutant glioma after radiation therapy (RT) is not well-defined. This study assesses practice patterns for managing recurrent IDH-mutant astrocytoma (Astro) and 1p/19q codeleted oligodendroglioma (Oligo) after RT and surveys their clinical outcomes after different salvage approaches.

Methods

Ninety-four recurrent Astro or Oligo patients after RT who received salvage systemic therapy (SST) between 2001 and 2019 at a tertiary cancer center were retrospectively analyzed. SST was defined as either alkylating chemotherapy (AC) or nonalkylating therapy (non-AC). Overall survival (OS) and progression-free survival (PFS) were calculated using the Kaplan-Meier method from the start of SST. Multivariable analysis (MVA) was conducted using Cox regression analysis.

Results

Recurrent Oligo (n = 35) had significantly higher PFS (median: 3.1 vs 0.8 years, respectively, P = .002) and OS (median: 6.3 vs 1.5 years, respectively, P < .001) than Astro (n = 59). Overall, 90% of recurrences were local. Eight-three percent received AC as the first-line SST; 50% received salvage surgery before SST; approximately 50% with local failure >2 years after prior RT received reirradiation. On MVA, non-AC was associated with worse OS for both Oligo and Astro; salvage surgery was associated with improved PFS and OS for Astro; early reirradiation was associated with improved PFS for Astro.

Conclusions

Recurrent radiation-relapsed IDH-mutant gliomas represent a heterogeneous group with variable treatment approaches. Surgery, AC, and reirradiation remain the mainstay of salvage options for retreatment.

Radiation-induced brain injury in patients with meningioma treated with proton or photon therapy

INTRODUCTION

Radiation therapy is often used to treat meningioma with adverse features or when unresectable. Proton therapy has advantages over photon therapy in reducing integral dose to the brain. This study compared the incidence of radiological and clinical adverse events after photon versus proton therapy in the treatment of meningioma.

METHODS

A retrospective review was conducted on patients with meningioma treated with proton or photon therapy at two high-volume tertiary cancer centers. Patients with a history of prior radiation therapy (RT) or less than 3 months of follow-up were excluded. Post-RT imaging changes were categorized into abnormal T2 signal intensities (T2 changes) or abnormal T1 post-contrast and T2 signal intensities (T1c+T2 changes) on magnetic resonance imaging (MRI). Clinical outcomes of adverse events and survival were compared between the proton and photon therapies.

RESULTS

Among the total of 77 patients, 38 patients received proton therapy and 39 patients received photon therapy. The median age at diagnosis was 55 years and median follow-up was 2.2 years. No significant differences in symptomatic adverse events were observed between the two groups: grade ≥ 2 adverse events were seen in 4 (10.5%) patients in the proton group and 3 (7.7%) patients in the photon group (p = 0.67). The 2-year cumulative incidences of T2 changes were 38.3% after proton therapy and 47.7% after photon therapy (p = 0.53) and the 2-year cumulative incidences of T1c+T2 changes were 26.8% after proton therapy and 5.3% after photon therapy (p = 0.02). One patient experienced grade ≥ 4 adverse event in each group (p = 0.99). Estimated 2-year progression-free survival was 79.5% (proton therapy 76.0% vs. photon therapy 81.3%, p = 0.66) and 2-year overall survival was 89.7% (proton therapy 86.6% vs. photon therapy 89.3%, p = 0.65).

CONCLUSIONS

Following RT, high rates of T2 changes were seen in meningioma patients regardless of treatment modality. Proton therapy was associated with significantly higher rates of T1c+T2 changes compared with photon therapy, but severe adverse events were uncommon in both groups and survival outcomes were comparable between the two groups. Future studies will aim at correlating the MRI changes with models that can be incorporated into RT planning to avoid toxicity.

Imaging Glioblastoma Posttreatment: Progression, Pseudoprogression, Pseudoresponse, Radiation Necrosis

Radiographic monitoring of posttreatment glioblastoma is important for clinical trials and determining next steps in management. Evaluation for tumor progression is confounded by the presence of treatment-related radiographic changes, making a definitive determination less straight-forward. The purpose of this article was to describe imaging tools available for assessing treatment response in glioblastoma, as well as to highlight the definitions, pathophysiology, and imaging features typical of true progression, pseudoprogression, pseudoresponse, and radiation necrosis.

Central Nervous System Cancers, Version 3.2020, NCCN Clinical Practice Guidelines in Oncology

The NCCN Guidelines for Central Nervous System (CNS) Cancers focus on management of adult CNS cancers ranging from noninvasive and surgically curable pilocytic astrocytomas to metastatic brain disease. The involvement of an interdisciplinary team, including neurosurgeons, radiation therapists, oncologists, neurologists, and neuroradiologists, is a key factor in the appropriate management of CNS cancers. Integrated histopathologic and molecular characterization of brain tumors such as gliomas should be standard practice. This article describes NCCN Guidelines recommendations for WHO grade I, II, III, and IV gliomas. Treatment of brain metastases, the most common intracranial tumors in adults, is also described.

A multi-institutional analysis of clinical outcomes and patterns of care of 1p/19q codeleted oligodendrogliomas treated with adjuvant or salvage radiation therapy

PURPOSE

Practice patterns vary for adjuvant treatment of 1p/19q-codeleted oligodendroglioma patients. This study evaluates the outcomes of adjuvant (aRT) versus salvage radiation therapy (sRT) in a multi-institutional cohort.

METHODS

Oligodendroglioma patients with confirmed 1p/19q codeletion who were treated with RT with or without chemotherapy from 2000 to 2017 at four tertiary centers were retrospectively reviewed. Overall survival (OS), post-RT progression-free survival (PFS), freedom-from-RT (FFRT), and radiation necrosis (RN) rates were determined using Kaplan-Meier analyses. OS1/PFS1 were defined from the initial surgery. OS2/PFS2 were defined from the RT start-date. Multivariable analyses (MVAs) of prognostic factors for OS and PFS were performed with Cox regression.

RESULTS

One hundred eighty-six patients were identified: 124(67%) received aRT and 62(33%) received sRT; of sRT patients, 58% were observed after surgery while 42% received chemotherapy without aRT. The median time from initial diagnosis to sRT was 61 months, and 74% had reoperations before sRT. sRT had longer OS1 than aRT (94% vs. 69% at 10 years, p = 0.03) and PFS1 (10-year PFS of 80% vs. 68%, p = 0.03), though sRT was not associated with significantly different OS1/PFS1 on MVAs. Chemotherapy did not delay sRT compared to observation and had worse PFS2 (42% vs. 79% at 5 years, p = 0.08). Higher RT dose was not associated with improved clinical outcomes but was associated with higher symptomatic RN rate (15% vs. 0% at 2 years, p = 0.003).

CONCLUSIONS

Delaying RT for selected oligodendroglioma patients appears safe. Adjuvant chemotherapy does not delay sRT longer than observation and may be associated with worse PFS after RT.

Volumetric and actuarial analysis of brain necrosis in proton therapy using a novel mixture cure model

BACKGROUND AND PURPOSE

High-dose fractionated radiotherapy is often necessary to achieve long-term tumor control in several types of tumors involving or within close proximity to the brain. There is limited data to guide on optimal constraints to the adjacent nontarget brain. This investigation explored the significance of the three-dimensional (3D) dose distribution of passive scattering proton therapy to the brain with other clinicopathological factors on the development of symptomatic radiation necrosis.

MATERIALS AND METHODS

All patients with head and neck, skull base, or intracranial tumors who underwent proton therapy (minimum prescription dose of 59.4 Gy(RBE)) with collateral moderate to high dose radiation exposure to the nontarget brain were retrospectively reviewed. A mixture cure model with respect to necrosis-free survival was used to derive estimates for the normal tissue complication probability (NTCP) model while adjusting for potential confounding factors.

RESULTS

Of 179 identified patients, 83 patients had intracranial tumors and 96 patients had primary extracranial tumors. The optimal dose measure obtained to describe the occurrence of radiation necrosis was the equivalent uniform dose (EUD) with parameter a = 9. The best-fit parameters of logistic NTCP models revealed D₅₀ = 57.7 Gy for intracranial tumors, D₅₀ = 39.5 Gy for extracranial tumors, and γ₅₀ = 2.5 for both tumor locations. Multivariable analysis revealed EUD and primary tumor location to be the strongest predictors of brain radiation necrosis.

CONCLUSION

In the current clinical volumetric data analyses with multivariable modelling, EUD was identified as an independent and strong predictor for brain radiation necrosis from proton therapy.

Imaging Glioblastoma Posttreatment: Progression, Pseudoprogression, Pseudoresponse, Radiation Necrosis

Radiographic monitoring of posttreatment glioblastoma is important for clinical trials and determining next steps in management. Evaluation for tumor progression is confounded by the presence of treatment-related radiographic changes, making a definitive determination less straight-forward. The purpose of this article was to describe imaging tools available for assessing treatment response in glioblastoma, as well as to highlight the definitions, pathophysiology, and imaging features typical of true progression, pseudoprogression, pseudoresponse, and radiation necrosis.

Quantifying effects of radiotherapy-induced microvascular injury; review of established and emerging brain MRI techniques

Microvascular changes are increasingly recognised not only as primary drivers of radiotherapy treatment response in brain tumours, but also as an important contributor to short- and long-term (cognitive) side effects arising from irradiation of otherwise healthy brain tissue. As overall survival of patients with brain tumours is increasing, monitoring long-term sequels of radiotherapy-induced microvascular changes in the context of their potential predictive power for outcome, such as cognitive disability, has become increasingly relevant. Ideally, radiotherapy-induced significant microvascular changes in otherwise healthy brain tissue should be identified as early as possible to facilitate adaptive radiotherapy and to proactively start treatment to minimise the influence on these side-effects on the final outcome. Although MRI is already known to be able to detect significant long-term radiotherapy induced microvascular effects, more recently advanced MR imaging biomarkers reflecting microvascular integrity and function have been reported and might provide a more accurate and earlier detection of microvascular changes. However, the use and validation of both established and new techniques in the context of monitoring early and late radiotherapy-induced microvascular changes in both target-tissue and healthy tissue currently are minimal at best. This review aims to summarise the performance and limitations of existing methods and future opportunities for detection and quantification of radiotherapy-induced microvascular changes, as well as the relation of these findings with key clinical parameters.

Management for Different Glioma Subtypes: Are All Low-Grade Gliomas Created Equal?

Following the identification of key molecular alterations that provided superior prognostication and led to the updated 2016 World Health Organization (WHO) Central Nervous System (CNS) Tumor Classification, the understanding of glioma behavior has rapidly evolved. Mutations in isocitrate dehydrogenase (IDH) 1 and 2 are present in the majority of adult grade 2 and 3 gliomas, and when used in conjunction with 1p/19q codeletion for classification, the prognostic distinction between grade 2 versus grade 3 is diminished. As such, the previously often used term of "low-grade glioma," which referred to grade 2 gliomas, has now been replaced by the phrase "lower-grade glioma" to encompass both grade 2 and 3 tumors. Additional molecular characterization is ongoing to even further classify this heterogeneous group of tumors. With such a colossal shift in the understanding of lower-grade gliomas, management of disease is being redefined in the setting of emerging molecular-genetic biomarkers. In this article, we review recent progress and future directions regarding the surgical, radiotherapeutic, chemotherapeutic, and long-term management of adult lower-grade gliomas.