Controversies in neuro-oncology: Focal proton versus photon radiation therapy for adult brain tumors

Radiation therapy (RT) plays a fundamental role in the treatment of malignant and benign brain tumors. Current state-of-the-art photon- and proton-based RT combines more conformal dose distribution of target volumes and accurate dose delivery while limiting the adverse radiation effects. PubMed was systematically searched from from 2000 to October 2023 to identify studies reporting outcomes related to treatment of central nervous system (CNS)/skull base tumors with PT in adults. Several studies have demonstrated that proton therapy (PT) provides a reduced dose to healthy brain parenchyma compared with photon-based (xRT) radiation techniques. However, whether dosimetric advantages translate into superior clinical outcomes for different adult brain tumors remains an open question. This review aims at critically reviewing the recent studies on PT in adult patients with brain tumors, including glioma, meningiomas, and chordomas, to explore its potential benefits compared with xRT.

Outcomes of Isocitrate Dehydrogenase Wild Type Glioblastoma after Re-irradiation

Purpose

Glioblastomas (GBM) are the most common malignant primary brain tumors in adults and have a dismal prognosis. Patients frequently suffer from local tumor recurrences, with limited therapeutic options. Re-irradiation represents a possible intervention, but given the recent 5th edition of the World Health Organization classification of central nervous system tumors, studies in isocitrate dehydrogenase wild type (IDH-wt) cohorts undergoing a second course of radiotherapy remain limited. Herein, we sought to describe our institutional experience and outcomes after GBM IDH-wt re-irradiation.

Materials and Methods

GBM patients with confirmed IDH-wt status undergoing re-irradiation were included in this single-center, retrospective analysis.

Results

A total of 88 patients were analyzed. The median clinical and radiographic follow-up periods were 4.6 months and 4.4 months, respectively. Most patients had a Karnofsky performance status of at least 80% (n = 57). The median biologically effective dose and 2 Gy equivalent dose (EQD2) for re-irradiations, assuming an α/β ratio of 10 Gy for GBM, were 51.4 and 42.8 Gy, respectively. In total, 71 deaths were recorded. The median overall survival (OS) was 8.0 months. Multivariable Cox regression of OS revealed a positive influence of gross total resection vs. biopsy or no resection (hazard ratio: 0.43, p = 0.02). The median progression-free survival (PFS) was 5.9 months. The multivariable Cox regression for PFS did not detect any significant factors. No clear evidence of radiation necrosis was recorded during the available follow-up. However, only a minority (n = 4) of patients underwent surgery after re-irradiation, none showing histopathological proof of radiation necrosis.

Conclusion

The prognosis for recurrent IDH-wt GBM after re-irradiation is poor. Patients who are amenable and able to undergo re-resection may have a favorable OS. A second course of radiotherapy with a moderate cumulative EQD2 and small- to medium-sized planning target volumes appeared safe regarding the occurrence of radiation necrosis.

Comparison of carbon ion and photon reirradiation for recurrent glioblastoma

PURPOSE

Purpose of this study was to investigate overall survival in recurrent glioblastoma treated with either carbon ion reirradiation or photon reirradiation.

MATERIALS AND METHODS

In this retrospective study we evaluated 78 consecutive patients with recurrent IDH (Isocitrate dehydrogenase)-wildtype glioblastoma (38 patients carbon ion re-radiotherapy, 40 patients photon re-radiotherapy) treated with either carbon ion reirradiation or stereotactic photon reirradiation. 45 Gy (RBE; 15 fractions) carbon ion reirradiation (CIRT) or 39 Gy (13 fractions) photon reirradiation (FSRT) was administered, respectively. Overall survival was investigated with respect to histological, clinical, and epidemiological features. Kaplan-Meier and multivariate Cox statistics were calculated. A propensity score-matched analysis of the FSRT and CIRT groups using variables from a validated prognosis score was carried out.

RESULTS

The type of reirradiation (CIRT vs. FSRT) significantly influenced overall survival-8.0 months vs. 6.5 months (univariate: p = 0.046)-and remained an independent prognostic factor in multivariate analysis (p = 0.017). Propensity score-adjusted analysis with CIRT versus FSRT as the dependent variable yielded a significant overall survival advantage for the CIRT group (median OS 8.9 versus 7.2 months, p = 0.041, 1‑year survival 29 versus 10%). Adverse events (AE) were evaluated for both subgroups. For the FSRT group no toxicity ≥ grade 4 occurred. For the CIRT subgroup no grade 5 AE occurred, but 1 patient developed a grade 4 radionecrosis. We encountered 4 grade 3 toxicities. One patient developed a zoster at the trunk, 2 progressed in their paresis, and 1 featured progressive dysesthesia.

CONCLUSION

In conclusion, carbon ion treatment is a safe and feasible treatment option for recurrent glioblastoma. Due to the retrospective nature of the study and two different dose levels for CIRT or FSRT, the improved outcome in CIRT reirradiation might be an effect of higher biological impact from carbon ions or a simple dose-escalation effect. This hypothesis needs prospective testing in larger patient cohorts. A prospective phase III randomized trial is in preparation at our center.

Relapsing High—Grade Glioma from Peritumoral Zone: Critical Review of Radiotherapy Treatment Options

Glioblastoma (GBM) is the most common and aggressive brain tumor in adults, with a median survival of about 15 months. After the prior treatment, GBM tends to relapse within the high dose radiation field, defined as the peritumoral brain zone (PTZ), needing a second treatment. In the present review, the primary role of ionizing radiation in recurrent GBM is discussed, and the current literature knowledge about the different radiation modalities, doses and fractionation options at our disposal is summarized. Therefore, the focus is on the necessity of tailoring the treatment approach to every single patient and using radiomics and PET/MRI imaging to have a relatively good outcome and avoid severe toxicity. The use of charged particle therapy and radiosensitizers to overcome GBM radioresistance is considered, even if further studies are necessary to evaluate the effectiveness in the setting of reirradiation.

A Clinical Case of 5 Times Irradiated Recurrent Orbital Hemangiopericytoma

Orbital hemangiopericytomas (HPCs) are rare mesenchymal tumors with a high tendency to recur. Treatment options are quite limited in case of a relapse, but re-irradiation can be useful. Most of the available data limit the possibility of re-irradiation, while novel techniques (e.g., pencil beam proton therapy [PT]) open new approaches for the safe repeating of treatment. To the best of our knowledge, this is the first well-documented case of multi-times (>3) irradiation of tumors located intracranially. The case reported here describes orbital HPCs with proton irradiation performed two times since 1999 in a 30-year-old woman with a medical history as well as surgery followed by conventional radiotherapy (RT) and chemotherapy, and two times stereotactic RT (in 2009 and 2013). In 2016 the patient came to our hospital with the 3rd relapse of the tumor, located in the left orbit, with an intracranial part, involving cavernous sinus, which was close to the temporal lobe. The 4th course of irradiation was done in May to June 2016 by pencil beam PT. Radiation necrosis occurred after 2 years and was treated with bevacizumab (BVZ). Three years later, another relapse was treated with PT and BVZ. The 9-month follow-up showed complete tumor response without signs of brain toxicity. The patient died due to a brain abscess 1 year after the 5th irradiation. This case shows a possibility of irradiation, applied 5 times to the same location, with promising results and manageable toxicity.

Dosimetric comparison of protons vs photons in re-irradiation of intracranial meningioma

OBJECTIVES

Re-irradiation of recurrent intracranial meningiomas represents a major challenge due to dose limits of critical structures and the necessity of sufficient dose coverage of the recurrent tumor for local control. The aim of this study was to investigate dosimetric differences between pencil beam scanning protons (PBS) and volumetric modulated arc therapy (VMAT) photons for intracranial re-irradiation of meningiomas.

METHODS

Nine patients who received an initial dose >50 Gy for intracranial meningioma and who were re-irradiated for recurrence were selected for plan comparison. A volumetric modulated arc therapy photon and a pencil beam scanning proton plan were generated (prescription dose: 15 × 3 Gy) based on the targets used in the re-irradiation treatment.

RESULTS

In all cases, where the cumulative dose exceeded 100 or 90 Gy, these high dose volumes were larger for the proton plans. The integral doses were significantly higher in all photon plans (reduction with protons: 48.6%, p < 0.01). In two cases (22.2%), organ at risk (OAR) sparing was superior with the proton plan. In one case (11.1%), the photon plan showed a dosimetric advantage. In the remaining six cases (66.7%), we found no clinically relevant differences in dose to the OARs.

CONCLUSIONS

The dosimetric results of the accumulated dose for a re-irradiation with protons and with photons were very similar. The photon plans had a steeper dose falloff directly outside the target and were superior in minimizing the high dose volumes. The proton plans achieved a lower integral dose. Clinically relevant OAR sparing was extremely case specific. The optimal treatment modality should be assessed individually.

ADVANCES IN KNOWLEDGE

Dose sparing in re-irradiation of intracranial meningiomas with protons or photons is highly case specific and the optimal treatment modality needs to be assessed on an individual basis.

Re-irradiation for recurrent glioblastoma (GBM): a systematic review and meta-analysis

PURPOSE

To determine the efficacy and toxicity of re-irradiation for patients with recurrent GBM.

MATERIALS AND METHODS

We searched various biomedical databases from 1998 to 2018, for eligible studies where patients were treated with re-irradiation for recurrent GBM. Outcomes of interest were 6 and 12-month overall survival (OS-6, OS-12), 6 and 12-month progression free survival (PFS-6, PFS-12) and serious (Grade 3 +) adverse events (AE). We used the random effects model to pool outcomes across studies and compared pre-defined subgroups using interaction test. Methodological quality of each study was assessed using the Newcastle-Ottawa scoring system.

RESULTS

We found 50 eligible non-comparative studies including 2095 patients. Of these, 42% were of good or fair quality. The pooled results were as follows: OS-6 rate 73% (95% confidence interval (CI) 69-77%), OS-12 rate 36% (95% CI 32-40%), PFS-6 rate 43% (95% CI 35-50%), PFS-12 rate 17% (95% CI 13-20%), and Grade 3 + AE rate 7% (95% CI 4-10%). Subgroup analysis showed that prospective studies reported higher toxicity rates, and studies which utilized brachytherapy to have a longer OS-12. Within the external beam radiotherapy group, there was no dose-response [above or below 36 Gy in 2 Gy equivalent doses (EQD2)]. However, a short fractionation regimen (≤ 5 fractions) seemed to provide superior PFS-6.

CONCLUSION

The available evidence, albeit mostly level III, suggests that re-irradiation provides encouraging disease control and survival rates. Toxicity was not uniformly reported, but seemed to be low from the included studies. Randomized controlled trials (RCT) are needed to establish the optimal management strategy for recurrent GBM.

Protons vs Photons for Brain and Skull Base Tumors

The physical characteristics of proton therapy result in steeper dose gradients and superior dose conformality compared to photon therapy. These properties render proton therapy ideal for skull base tumors requiring dose escalation for optimal tumor control, and may also be beneficial for brain tumors as a means of mitigating radiation-related adverse effects. This review summarizes the literature regarding the role of proton therapy compared to photon therapy in the treatment of adult brain and skull base tumors.

Multimodal treatment for local recurrent malignant gliomas: Resurgery and/or reirradiation followed by chemotherapy

The therapeutic management of recurrent malignant gliomas (MGs) is not determined. Therefore, the efficacy of a multimodal approach and a combination systemic therapy was investigated. A retrospective analysis of 26 MGs patients at first relapse treated with multimodal therapy (chemotherapy plus surgery and/or reirradiation) or chemotherapy alone was performed. Second-line chemotherapy consisted of fotemustine (FTM) in combination with bevacizumab (BEV) (cFTM/BEV) or followed by third-line BEV (sFTM/BEV). Subgroup analyses were performed. Multimodal therapy provided a higher overall response rate (ORR) (73 vs. 47%), disease control rate (DCR) (82 vs. 67%), median progression-free survival (mPFS) (11 vs. 7 months; P=0.08) and median overall survival (mOS) (13 vs. 8 months; P=0.04) compared with chemotherapy. Concomitant FTM/BEV resulted in higher ORR (84 vs. 36%), DCR (92 vs. 57%), mPFS (10 vs. 5 months; P=0.22) and mOS (11 vs. 5.2 months; P=0.15) compared with sFTM/BEV. Methylated patients did not experience additional survival benefits with multimodality treatment but had higher mPFS (10 vs 7.1 months; P=0.33) and mOS (11 vs. 8 months; P=0.33) with cFTM/BEV. Unmethylated patients experienced the greatest survival benefit with the multimodal approach (mPFS: 10 vs. 5 months; mOS 11 vs 6 months; both P=0.02) and cFTM/BEV (mPFS: 5 vs. 2 months; mOS 6 vs. 3.2 months; both P=0.01). In conclusion, in recurrent MGs, multimodal therapy and cFTM/BEV provide survival and response benefits. Methylated patients benefit from a cFTM/BEV but not from a multimodal approach. Notably, unmethylated patients had the highest survival benefit with the two strategies.

Glioblastoma Treatments: An Account of Recent Industrial Developments

The different drugs and medical devices, which are commercialized or under industrial development for glioblastoma treatment, are reviewed. Their different modes of action are analyzed with a distinction being made between the effects of radiation, the targeting of specific parts of glioma cells, and immunotherapy. Most of them are still at a too early stage of development to firmly conclude about their efficacy. Optune, which triggers antitumor activity by blocking the mitosis of glioma cells under the application of an alternating electric field, seems to be the only recently developed therapy with some efficacy reported on a large number of GBM patients. The need for early GBM diagnosis is emphasized since it could enable the treatment of GBM tumors of small sizes, possibly easier to eradicate than larger tumors. Ways to improve clinical protocols by strengthening preclinical studies using of a broader range of different animal and tumor models are also underlined. Issues related with efficient drug delivery and crossing of blood brain barrier are discussed. Finally societal and economic aspects are described with a presentation of the orphan drug status that can accelerate the development of GBM therapies, patents protecting various GBM treatments, the different actors tackling GBM disease, the cost of GBM treatments, GBM market figures, and a financial analysis of the different companies involved in the development of GBM therapies.

External beam re-irradiation, combination chemoradiotherapy, and particle therapy for the treatment of recurrent glioblastoma

Glioblastoma is a common aggressive primary malignant brain tumor, and is nearly universal in progression and mortality after initial treatment. Re-irradiation presents a promising treatment option for progressive disease, both palliating symptoms and potentially extending survival. Highly conformal radiation techniques such as stereotactic radiosurgery and hypofractionated radiosurgery are effective short courses of treatment that allow delivery of high doses of therapeutic radiation with steep dose gradients to protect normal tissue. Patients with higher performance status, younger age, and longer interval between primary treatment and progression represent the best candidates for re-irradiation. Multiple studies are also underway involving combinations of radiation and systemic therapy to bend the survival curve and improve the therapeutic index. In the multimodal treatment of recurrent high-grade glioma, the use of surgery, radiation, and systemic therapy should be highly individualized. Here we comprehensively review radiation therapy and techniques, along with discussion of combination treatment and novel strategies.