Do Increased Doses to Stem-Cell Niches during Radiation Therapy Improve Glioblastoma Survival?

Therapy Resistance of Glioblastoma in Relation to the Subventricular Zone: What Is the Role of Radiotherapy?

Glioblastoma is a highly heterogeneous primary malignant brain tumor with marked inter-/intratumoral diversity and a poor prognosis. It may contain a population of neural stem cells (NSC) and glioblastoma stem cells that have the capacity for migration, self-renewal and differentiation. While both may contribute to resistance to therapy, NSCs may also play a role in brain tissue repair. The subventricular zone (SVZ) is the main reservoir of NSCs. This study investigated the impact of bilateral SVZ radiation doses on patient outcomes. We included 147 patients. SVZs were delineated and the dose administered was extracted from dose–volume histograms. Tumors were classified based on their spatial relationship to the SVZ. The dose and outcome correlations were analyzed using the Kaplan–Meier and Cox proportional hazards regression methods. Median progression-free survival (PFS) was 7 months (range: 4–11 months) and median overall survival (OS) was 14 months (range: 9–23 months). Patients with an ipsilateral SVZ who received ≥50 Gy showed significantly better PFS (8 versus 6 months; p < 0.001) and OS (16 versus 11 months; p < 0.001). Furthermore, lower doses (<32 Gy) to the contralateral SVZ were associated with improved PFS (8 versus 6 months; p = 0.030) and OS (15 versus 11 months; p = 0.001). Targeting the potential tumorigenic cells in the ipsilateral SVZ while sparing contralateral NSCs correlated with an improved outcome. Further studies should address the optimization of dose distribution with modern radiotherapy techniques for the areas surrounding infiltrated and healthy SVZs.

Glioma radiogenomics and artificial intelligence: road to precision cancer medicine

Radiogenomics refers to the study of the relationship between imaging phenotypes and gene expression patterns/molecular characteristics, which might allow improved diagnosis, decision-making, and predicting patient outcomes in the context of multiple diseases. Central nervous system (CNS) tumours contribute to significant cancer-related mortality in the present age. Although historically CNS neoplasms were classified and graded based on microscopic appearance, there was discordance between two histologically similar tumours that showed varying prognosis and behaviour, attributable to their molecular signatures. These led to the incorporation of molecular markers in the classification of CNS neoplasms. Meanwhile, advancements in imaging technology such as diffusion-based imaging (including tractography), perfusion, and spectroscopy in addition to the conventional imaging of glial neoplasms, have opened an avenue for radiogenomics. This review touches upon the schema of the current classification of gliomas, concepts behind molecular markers, and parameters that are used in radiogenomics to characterise gliomas and the role of artificial intelligence for the same. Further, the role of radiomics in the grading of brain tumours, prediction of treatment response and prognosis has been discussed. Use of automated and semi-automated tumour segmentation for radiotherapy planning and follow-up has also been discussed briefly.

DNA-methylome-assisted classification of patients with poor prognostic subventricular zone associated IDH-wildtype glioblastoma

Glioblastoma (GBM) derived from the “stem cell” rich subventricular zone (SVZ) may constitute a therapy-refractory subgroup of tumors associated with poor prognosis. Risk stratification for these cases is necessary but is curtailed by error prone imaging-based evaluation. Therefore, we aimed to establish a robust DNA methylome-based classification of SVZ GBM and subsequently decipher underlying molecular characteristics. MRI assessment of SVZ association was performed in a retrospective training set of IDH-wildtype GBM patients (n = 54) uniformly treated with postoperative chemoradiotherapy. DNA isolated from FFPE samples was subject to methylome and copy number variation (CNV) analysis using Illumina Platform and cnAnalysis450k package. Deep next-generation sequencing (NGS) of a panel of 130 GBM-related genes was conducted (Agilent SureSelect/Illumina). Methylome, transcriptome, CNV, MRI, and mutational profiles of SVZ GBM were further evaluated in a confirmatory cohort of 132 patients (TCGA/TCIA). A 15 CpG SVZ methylation signature (SVZM) was discovered based on clustering and random forest analysis. One third of CpG in the SVZM were associated with MAB21L2/LRBA. There was a 14.8% (n = 8) discordance between SVZM vs. MRI classification. Re-analysis of these patients favored SVZM classification with a hazard ratio (HR) for OS of 2.48 [95% CI 1.35–4.58], p = 0.004 vs. 1.83 [1.0–3.35], p = 0.049 for MRI classification. In the validation cohort, consensus MRI based assignment was achieved in 62% of patients with an intraclass correlation (ICC) of 0.51 and non-significant HR for OS (2.03 [0.81–5.09], p = 0.133). In contrast, SVZM identified two prognostically distinct subgroups (HR 3.08 [1.24–7.66], p = 0.016). CNV alterations revealed loss of chromosome 10 in SVZM– and gains on chromosome 19 in SVZM– tumors. SVZM– tumors were also enriched for differentially mutated genes (p < 0.001). In summary, SVZM classification provides a novel means for stratifying GBM patients with poor prognosis and deciphering molecular mechanisms governing aggressive tumor phenotypes.

Ventricle wall resection contributes to supramaximal resection and prognosis in SVZ-involved frontal gliomas: A single center retrospective study

BACKGROUND

Frontal glioma frequently invaded the subventricular zone (SVZ), which existed glioma stem cells and might be involved in the development of primary and recurrent gliomas. We attempted to identify whether ventricle wall resection contributed to the maximal extent of resection (EOR) and increased the patient's survival during frontal glioma resection.

METHODS

A total of 151 adult patients with primary SVZ-involved frontal gliomas were obtained between January 2012 and December 2018. We analyzed clinical data, EOR, complications and survival profiles between the ventricle wall group and the ventricle intact/opening group.

RESULTS

Applying ventricle wall removal had similar effect on the improvement of neurological function compared to applying ventricle intact/opening and did not increase the incidence of new neurological deficits, hydrocephalus, and ependymal dissemination in SVZ-involved frontal gliomas. A positive correlation was identified between EOR and the ventricle wall handling (r = 0.487, P < 0.001), which indicated that ventricle wall resection could contribute to achieve supramaximal resection. Applying supramaximal resection and ventricle wall resection could significantly prolong overall survival and progression free survival. Ventricle wall resection could be regarded as an independent prognostic indicator for both overall survival and progression free survival in patients with SVZ-involved frontal gliomas.

CONCLUSIONS

Ventricle wall resection in SVZ-involved frontal gliomas could contribute to achieve supramaximal resection and could significantly prolong overall survival and progression free survival.

Survival impact of incidental subventricular zone irradiation in IDH-wildtype glioblastoma

BACKGROUND AND PURPOSE

The subventricular zone (SVZ) is an important niche for neural stem cells but probably also for brain tumor propagating cells, including the glioblastoma stem cell. The SVZ may become a target for radiation therapy in glioblastoma patients. However, reports studying the effect of irradiation of the SVZ on glioblastoma patient survival show conflicting results. We studied the correlation between incidental SVZ radiation dose and survival in a cohort of isocitrate dehydrogenase-wildtype (IDHwt) glioblastoma patients with inclusion of important survival prognosticators.

PATIENTS AND METHODS

In this retrospective analysis, only adult patients with supratentorial IDHwt glioblastoma were included who were treated with temozolomide-based chemoradiotherapy after surgery. The SVZ was contoured on the radiotherapy planning imaging. Cox proportional regression overall survival (OS) analysis was used to study the correlation between SVZ dose and survival. Age, Karnofsky Performance Score, extent of resection and O⁶-methylguanine-methyl-DNA-transferase gene promoter (MGMTp) methylation were used as covariates in multivariate analysis.

RESULTS

In total, 137 patients were included. Median OS was 13.3 months. The MGMTp methylation was present in 40% of cases. Ipsilateral SVZ (iSVZ) mean dose was 44.4 Gy and 27.2 Gy for the contralateral SVZ (cSVZ). Univariate survival analysis showed an inverse relationship between cSVZ mean dose and OS (HR 1.029 (1.003-1.057); p= .032). However, there was no correlation between cSVZ mean dose and OS in multivariate analysis. iSVZ dose did not correlate with survival.

CONCLUSION

In this cohort of 137 IDHwt glioblastoma patients, iSVZ did not correlate with OS. Higher cSVZ dose was inversely correlated with OS in univariate survival analysis but lost its significance in multivariate analysis, including MGMTp-methylation. Hence, the correlation between SVZ radiation and glioblastoma patient survival remains unclear. Carefully designed prospective studies are needed to provide unequivocal results on this controversial topic.

What is the role of the subventricular zone in radiotherapy of glioblastoma patients?

BACKGROUND AND PURPOSE

Current glioblastoma (GBM) therapies prolong survival, but overall prognosis is still poor. Irradiation of the subventricular zone (SVZ) has recently been discussed as a promising concept as this tissue harbors stem cells which seem to play a role in the initiation and recurrence of GBM. In this study, we retrospectively examined the relationship of SVZ irradiation dose and survival in a large, homogeneous GBM patient cohort.

MATERIALS AND METHODS

We included 200 GBM patients who had been treated at our institution with trimodal therapy (surgery, radiotherapy and chemotherapy) between 2009 and 2020. The SVZ was delineated, and dose-volume histograms were calculated and extracted. Tumors were classified according to their contact with the SVZ. The Kaplan-Meier method was used for survival analysis, and univariable and multivariable Cox regression (MVA) were used to determine prognostic effects on progression-free survival (PFS) and overall survival (OS).

RESULTS

Median PFS of the study group was 7.2 months; median OS was 15.1 months. In MVA (with mean dose to the ipsilateral SVZ as a continuous covariable), PFS was significantly lower for patients with a Karnofsky performance status (KPS) < 70% and without MGMT promoter methylation. Factors prognostic for shorter OS were old age, lower KPS, unmethylated MGMT status, SVZ contact and biopsy instead of subtotal- or gross total resection. There was no significant correlation between survival and SVZ dose.

CONCLUSION

In this cohort, an increased mean dose to the ipsilateral or contralateral SVZ did not correlate with improved survival in irradiated GBM patients in MVA. Patients whose tumor directly involved the SVZ showed worse OS in MVA.

Prospective study to assess the survival outcomes of planned irradiation of ipsilateral subventricular and periventricular zones in glioblastoma

Purpose/objective(s)

Retrospective evidence suggests that the irradiation of stem cells in the periventricular zone (PVZ), specifically the subventricular zone (SVZ), to higher doses may be associated with improved outcomes.

Materials/methods

This was a prospective study, done from 2012 to 2017 in glioblastoma patients to assess the efficacy of planned irradiation of ipsilateral PVZ and SVZ on survival outcomes. The clinical target volume included the tumour bed with a 1.5–2 cm margin, perilesional oedema and was expanded to encompass the ipsilateral PVZ (5 mm lateral expansion adjacent to the ventricles, including the SVZ, which was a 5 mm expansion lateral to lateral ventricle). The ipsilateral PVZ was planned to receive a dose of ≥50 Gy.

Results

89 patients were recruited of which 74 patients were available for the analysis. Median age was 48 years. Mean doses to ipsilateral PVZ and SVZ were 56.2 and 55.1Gy, respectively. Median overall survival in the entire group was 13 months. There was no significant correlation between survival and doses to ipsilateral, contralateral, or bilateral PVZ and SVZ. Median survival was 16, 12 and 6 months for Eastern Cooperative ­Oncology Group (ECOG) PS 1, 2 and 3, respectively (p = 0.05).

Conclusion

Planned irradiation of potential stem cell niches in the ipsilateral cerebral hemisphere did not result in improved survival as suggested by retrospective studies. Doses to contralateral or bilateral PVZ or SVZ also did not influence survival.

The Role of SVZ Stem Cells in Glioblastoma

As most common primary brain cancer, glioblastoma is also the most aggressive and malignant form of cancer in the adult central nervous system. Glioblastomas are genetic and transcriptional heterogeneous tumors, which in spite of intensive research are poorly understood. Over the years conventional therapies failed to affect a cure, resulting in low survival rates of affected patients. To improve the clinical outcome, an important approach is to identify the cells of origin. One potential source for these are neural stem cells (NSCs) located in the subventricular zone, which is one of two niches in the adult nervous system where NSCs with the capacity of self-renewal and proliferation reside. These cells normally give rise to neuronal as well as glial progenitor cells. This review summarizes current findings about links between NSCs and cancer stem cells in glioblastoma and discusses current therapeutic approaches, which arise as a result of identifying the cell of origin in glioblastoma.

Locally dose-escalated radiotherapy may improve intracranial local control and overall survival among patients with glioblastoma

Background

The dismal overall survival (OS) prognosis of glioblastoma, even after trimodal therapy, can be attributed mainly to the frequent incidence of intracranial relapse (ICR), which tends to present as an in-field recurrence after a radiation dose of 60 Gray (Gy). In this study, molecular marker-based prognostic indices were used to compare the outcomes of radiation with a standard dose versus a moderate dose escalation.

Methods

This retrospective analysis included 156 patients treated between 2009 and 2016. All patients were medically fit for postoperative chemoradiotherapy. In the dose-escalation cohort a simultaneous integrated boost of up to 66 Gy (66 Gy RT) within small high-risk volumes was applied. All other patients received daily radiation to a total dose of 60 Gy or twice daily to a total dose of 59.2 Gy (60 Gy RT).

Results

A total of 133 patients received standard 60 Gy RT, while 23 received 66 Gy RT. Patients in the 66 Gy RT group were younger (p <  0.001), whereas concomitant temozolomide use was more frequent in the 60 Gy RT group (p <  0.001). Other intergroup differences in known prognostic factors were not observed. Notably, the median time to ICR was significantly prolonged in the 66 Gy RT arm versus the 60 Gy RT arm (12.2 versus 7.6 months, p = 0.011), and this translated to an improved OS (18.8 versus 15.3 months, p = 0.012). A multivariate analysis revealed a strong association of 66 Gy RT with a prolonged time to ICR (hazard ratio = 0.498, p = 0.01) and OS (hazard ratio = 0.451, p = 0.01). These differences remained significant after implementing molecular marker-based prognostic scores (ICR p = 0.008, OS p = 0.007) and propensity-scored matched pairing (ICR p = 0.099, OS p = 0.023).

Conclusion

Radiation dose escalation was found to correlate with an improved time to ICR and OS in this cohort of glioblastoma patients. However, further prospective validation of these results is warranted.

Electronic supplementary material

The online version of this article (10.1186/s13014-018-1194-8) contains supplementary material, which is available to authorized users.

Subventricular Zone Radiation Dose and Outcome for Glioblastoma Treated Between 2006 and 2012

Objective Stem cells residing in the subventricular zone (SVZ) may be related to recurrence, potentially affecting outcome in glioblastoma (GBM). This study investigated the relationship of SVZ radiation dose and survival in a large cohort treated with surgery and chemoradiotherapy (CRT). Methods Patients with GBM treated between 2006 and 2012 (n = 370) were identified. SVZs were contoured from planning computed tomography (CT) with magnetic resonance imaging (MRI) registration where available. Dose was extracted from dose volume histograms. Kaplan-Meier (KM) progression-free survival (PFS) and overall survival (OS) estimates were compared with log-rank tests for SVZ doses. Multivariate analysis (MVA) identified clinical and treatment-related factors significantly associated with outcome. Results Median follow-up was 16.4 months, 48.1% underwent gross total resection (GTR), 37.5% subtotal resection, and 14.4% biopsy without resection. Median PFS was 8.9 months (95% CI: 8.3-9.8 months), and OS was 16.5 months (95% CI: 15.2-17.6 months). PFS was significantly lower for older age (>50 years, P = 0.045), poor Karnofsky performance status (KPS, P = 0.049), multifocality (P < 0.001), and incomplete adjuvant chemotherapy (P < 0.001). Worse OS was associated with poor KPS (P = 0.001), biopsy only (P = 0.003), multifocality (P = 0.009), and failure to complete adjuvant chemotherapy (P < 0.001). SVZ dose was not associated with outcome for any of the dose levels assessed. On MVA, multifocality was associated with worse PFS (P < 0.01). Poor performance status and biopsy only were associated with worse OS (both P < 0.01). Conclusion In this analysis of a large cohort of GBM treated with surgery and CRT, increased SVZ dose was not associated with improved survival.

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

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

Subventricular zones: new key targets for glioblastoma treatment

Background

We aimed to identify subventricular zone (SVZ)-related prognostic factors of survival and patterns of recurrence among patients with glioblastoma.

Methods

Forty-three patients with primary diagnosed glioblastoma treated in our Cancer Center between 2006 and 2010 were identified. All patients received surgical resection, followed by temozolomide-based chemoradiation. Ipsilateral (iSVZ), contralateral (cSVZ) and bilateral (bSVZ) SVZs were retrospectively segmented and radiation dose-volume histograms were generated. Multivariate analysis using the Cox proportional hazards model was assessed to examine the relationship between prognostic factors and time to progression (TTP) or overall survival (OS).

Results

Median age was 59 years (range: 25–85). Median follow-up, OS and TTP were 22.7 months (range 7.5–69.7 months), 22.7 months (95% CI 14.5–26.2 months) and 6.4 months (95% CI 4.4–9.3 months), respectively. On univariate analysis, initial contact to SVZ was a poor prognostic factor for OS (18.7 vs 41.7 months, p = 0.014) and TTP (4.6 vs 12.9 months, p = 0.002). Patients whose bSVZ volume receiving at least 20 Gy (V20Gy) was greater than 84% had a significantly improved TTP (17.7 months vs 5.2 months, p = 0.017). This radiation dose coverage was compatible with an hippocampal sparing. On multivariate analysis, initial contact to SVZ and V20 Gy to bSVZ lesser than 84% remained poor prognostic factors for TTP (HR = 3.07, p = 0.012 and HR = 2.67, p = 0.047, respectively).

Conclusion

Our results suggest that contact to SVZ, as well as insufficient bSVZ radiation dose coverage (V20Gy <84%), might be independent poor prognostic factors for TTP. Therefore, targeting SVZ could be of crucial interest for optimizing glioblastoma treatment.