Stereotactic proton beam therapy of skull base meningiomas

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.

How proton therapy fits into the management of adult intracranial tumors

Intracranial tumors include a challenging array of primary and secondary parenchymal and extra-axial tumors which cause neurologic morbidity consequential to location, disease extent, and proximity to critical neurologic structures. Radiotherapy can be used in the definitive, adjuvant, or salvage setting either with curative or palliative intent. Proton therapy (PT) is a promising advance due to dosimetric advantages compared to conventional photon radiotherapy with regards to normal tissue sparing, as well as distinct physical properties, which yield radiobiologic benefits. In this review, the principles of efficacy and safety of PT for a variety of intracranial tumors are discussed, drawing upon case series, retrospective and prospective cohort studies, and randomized clinical trials. This manuscript explores the potential advantages of PT, including reduced acute and late treatment-related side effects and improved quality of life. The objective is to provide a comprehensive review of the current evidence and clinical outcomes of PT. Given the lack of consensus and directives for its utilization in patients with intracranial tumors, we aim to provide a guide for its judicious use in clinical practice.

Hypofractionated proton therapy for benign tumors of the central nervous system: A systematic review of the literature

AIMS

Aim of the present analysis was to report results of a systematic review of the literature in the setting of patients treated with hypoF PT for benign lesions of the central nervous system (CNS).

METHODS

The methodology complied with the PRISMA recommendations. PubMed, EMBASE and Scopus databases were interrogated in September 2022.

RESULTS

Twelve papers have been selected including patients treated for base of the skull meningiomas (6 papers), vestibular schwannoma (3 papers) and pituitary adenomas (3 papers). Clinical outcomes were evaluated with both radiologic images and clinical parameters. Long-term toxicity was reported in all but one series with an incidence ranging from 2 % to 7 % in patients treated for base of skull meningioma and 1-9 % for schwannoma.

CONCLUSIONS

HypoF PT is a safe and effective treatment in selected benign tumors of the CNS. Further dosimetric and clinical comparisons are required to better refine the patients' selection criteria.

The role of particle radiotherapy in the treatment of skull base tumors

The skull base is an anatomically and functionally critical area surrounded by vital structures such as the brainstem, the spinal cord, blood vessels, and cranial nerves. Due to this complexity, management of skull base tumors requires a multidisciplinary approach involving a team of specialists such as neurosurgeons, otorhinolaryngologists, radiation oncologists, endocrinologists, and medical oncologists. In the case of pediatric patients, cancer management should be performed by a team of pediatric-trained specialists. Radiation therapy may be used alone or in combination with surgery to treat skull base tumors. There are two main types of radiation therapy: photon therapy and particle therapy. Particle radiotherapy uses charged particles (protons or carbon ions) that, due to their peculiar physical properties, permit precise targeting of the tumor with minimal healthy tissue exposure. These characteristics allow for minimizing the potential long-term effects of radiation exposure in terms of neurocognitive impairments, preserving quality of life, and reducing the risk of radio-induced cancer. For these reasons, in children, adolescents, and young adults, proton therapy should be an elective option when available. In radioresistant tumors such as chordomas and sarcomas and previously irradiated recurrent tumors, particle therapy permits the delivery of high biologically effective doses with low, or however acceptable, toxicity. Carbon ion therapy has peculiar and favorable radiobiological characteristics to overcome radioresistance features. In low-grade tumors, proton therapy should be considered in challenging cases due to tumor volume and involvement of critical neural structures. However, particle radiotherapy is still relatively new, and more research is needed to fully understand its effects. Additionally, the availability of particle therapy is limited as it requires specialized equipment and expertise. The purpose of this manuscript is to review the available literature regarding the role of particle radiotherapy in the treatment of skull base tumors.

Meningioma WHO I with involvement of the optical structures-does proton therapy lead to changes in quality of life with regard to subjective visual performance?

BACKGROUND

In addition to local tumor control, the aim of any curative radio-oncological treatment is to maintain quality of life. In the treatment of patients with meningioma with a close relationship to optical structures, the preservation of visual performance is a particular challenge. Use of proton therapy can reduce the dose burden to organs at risk immediately adjacent to the tumor. The aim of this study was to score the subjective assessment of visual performance in patients with meningioma involving the optical structures before and after proton therapy.

METHODS

All proton-treated patients with meningioma WHO I whose planning target volumes (PTV) included parts of the optic nerve and/or chiasm were included in this study. Subjective assessment of visual performance was evaluated using the Visual Disorder Scale (VDS) of the EORTC QLQ-BN20 questionnaire. This scale includes values from 0 to 100, whereby high values reflect a high degree of subjective symptom burden and thus subjective visual impairment. The visual acuity in externally performed eye tests at baseline and follow-ups (FU) was also evaluated. The timepoints for testing were before the start of radiotherapy, at the end of treatment, and 3, 6, 12, and 24 months in FU (times t1-t6). All patients with at least the first annual postradiation FU at the time of the evaluation were included. The correlation between VDS changes and potential influencing factors such as previous therapies, dosimetric data, initial tumor volume, and tumor shrinkage 1 year after treatment was assessed.

RESULTS

A total of 56 patients (45 female/11 male) aged 24-82 years (mean ± SD = 53.9 ± 13.3) treated between March 2017 and September 2019 were included in the analysis. The prescription dose was 54.0 Gy (RBE) with active scanned proton therapy. The mean/D2% dose ± SD for the optic chiasm and ipsilateral optic nerve was 43.4 ± 8.9 Gy (RBE)/49.9 ± 7.1 Gy (RBE) and 35.6 ± 11.7 Gy (RBE)/51.7 ± 4.8 Gy (RBE); the mean/D2% dose ± SD of the contralateral optic nerve was 18.8 ± 12.1 Gy (RBE)/42.4 ± 14.6 Gy (RBE), respectively. A total of 302 data collections were available (t1/t2/t3/t4/t5/t6: n = 56/56/48/56/52/34). Median observation time was 23.6 months. Mean symptom burden decreased over time (mean VDS: t1 29.8 ± 27.9; t2 25.0 ± 27.9; t3 21.8 ± 26.0; t4 22.2 ± 26.0; t5 21.4 ± 26.2; t6 17.3 ± 23.6) with statistically significant improvement at 3‑ and 6‑month FU as well as 1 year after proton therapy (p = 0.0205; p = 0.0187; p = 0.0054). Objective eye tests available in 41/52 patients confirm the trend towards improved visual acuity (97.5% stable/improved until 24-month FU). However, no potential predictor for VDS changes was revealed.

CONCLUSION

Proton treatment of patients with meningioma WHO I with involvement of optical structures does not impair subjective visual performance. After treatment, there is a significant improvement in perceived visual performance.

Dose-staged Gamma Knife radiosurgery for meningiomas: A retrospective study in a single center

Objective

This study aimed to study the efficiency and safety of a dose-staged Gamma Knife radiosurgery strategy for large meningiomas or meningiomas close to important nerve structures.

Methods

This study evaluates the outcome of a prospectively accrued series of 71 consecutive patients with meningiomas treated with staged dose-fractionated Gamma Knife radiosurgery. The average peripheral doses for the first and second fractions were 9.0 ± 0.9 Gy (8–12 Gy) and 8.6 ± 0.7 Gy (range, 7–10 Gy), respectively. The interval between fractions was 6.1 ± 1.9 months (range, 3–12 months). The median follow-up time was 36 months (12–96 months).

Results

During the follow-up period after the second fraction, 97.2% achieved tumor control in our series. A total of 2 patients exhibited local recurrence at 30 and 60 months after the second fraction, respectively. No treatment-related complications or new long-term neurological dysfunctions were reported. MRIs observed slightly or moderately increased peritumoral edema in six patients, but no specific neurological complaints are attributed to this finding.

Conclusion

This study investigates the efficiency and safety of dose-staged Gamma Knife radiosurgery as an alternative option for meningiomas that were large in volume, adjacent to crucial structures, or in patients with contraindications to craniotomy.

Management of Recurrent Meningiomas: State of the Art and Perspectives

Simple Summary

Intracranial meningiomas account for 30% to 40% of the primary lesions of the central nervous system. Surgery is the mainstay treatment whenever symptoms related to an intra-cranial meningioma are encountered. However, the management of recurrences after initial surgery, which are not uncommon, is still a matter of debate. Here, we present the alternatives described in the management of meningioma recurrence (radiotherapy, stereotaxic radiosurgery, protontherapy, and chemotherapy, among others). Their overall results are compared to surgery and future perspectives are presented.

Abstract

Background: While meningiomas often recur over time, the natural history of repeated recurrences and their management are not well described. Should recurrence occur, repeat surgery and/or use of adjuvant therapeutic options may be necessary. Here, we summarize current practice when it comes to meningioma recurrence after initial surgical management. Methods: A total of N = 89 articles were screened. N = 41 articles met the inclusion criteria and N = 16 articles failed to assess management of meningioma recurrence. Finally, N = 24 articles were included in our review. Results: The articles were distributed as follows: studies on chemotherapy (N = 14), radiotherapy, protontherapy, and stereotaxic radiosurgery (N = 6), boron-neutron capture therapy (N = 2) and surgery (N = 3). No study seems to provide serious alternatives to surgery in terms of progression-free and overall survival. Recurrence can occur long after the initial surgery and also affects WHO grade 1 meningiomas, even after initial gross total resection at first surgery, emphasizing the need for a long-term and comprehensive follow-up. Conclusions: Surgery still seems to be the state-of-the-art management when it comes to meningioma recurrence, since none of the non-surgical alternatives show promising results in terms of progression-free and overall survival.

The Role of Hypofractionation in Proton Therapy

Hypofractionated radiotherapy is an attractive approach for minimizing patient burden and treatment cost. Technological advancements in external beam radiotherapy (EBRT) delivery and image guidance have resulted in improved targeting and conformality of the absorbed dose to the disease and a reduction in dose to healthy tissue. These advances in EBRT have led to an increasing adoption and interest in hypofractionation. Furthermore, for many treatment sites, proton beam therapy (PBT) provides an improved absorbed dose distribution compared to X-ray (photon) EBRT. In the past 10 years there has been a notable increase in reported clinical data involving hypofractionation with PBT, reflecting the interest in this treatment approach. This review will discuss the reported clinical data and radiobiology of hypofractionated PBT. Over 50 published manuscripts reporting clinical results involving hypofractionation and PBT were included in this review, ~90% of which were published since 2010. The most common treatment regions reported were prostate, lung and liver, making over 70% of the reported results. Many of the reported clinical data indicate that hypofractionated PBT can be well tolerated, however future clinical trials are still needed to determine the optimal fractionation regime.

Radiation therapy for atypical and anaplastic meningiomas: an overview of current results and controversial issues

Meningiomas are the most common intracranial tumors. Most meningiomas are WHO grade 1 tumors whereas less than one-quarter of all meningiomas are classified as atypical (WHO grade 2) and anaplastic (WHO grade 3) tumors, based on local invasiveness and cellular features of atypia. Surgical resection remains the cornerstone of meningioma therapy and represents the definitive treatment for the majority of patients; however, grade 2 and grade 3 meningiomas display more aggressive behavior and are difficult to treat. Several retrospective series have shown the efficacy and safety of postoperative adjuvant external beam radiation therapy (RT) for patients with atypical and anaplastic meningiomas. More recently, two phase II prospective trials by the Radiation Therapy Oncology Group (RTOG 0539) and the European Organisation for Research and Treatment of Cancer (EORTC 2042) have confirmed the potential benefits of fractionated RT for patients with intermediate and high-risk meningiomas; however, several issues remain a matter of debate. Controversial topics include the timing of radiation treatment in patients with totally resected atypical meningiomas, the optimal radiation technique, dose and fractionation, and treatment planning/target delineation. Ongoing randomized trials are evaluating the efficacy of early adjuvant RT over observation in patients undergoing gross total resection.

Outcome After Protontherapy for Progression or Recurrence of Surgically Treated Meningioma

Background

To assess the outcome after meningioma surgery and protontherapy (PT).

Methods

We processed the French Système National des Données de Santé database to retrieve appropriate cases of meningiomas operated and irradiated between 2008 and 2017. Survival methods were implemented.

Results

One hundred ninety-three patients who received PT after meningioma surgery over a 10-year period were identified. Of the 193 patients, 75.6% were female. Median age at surgery was 50 years (interquartile range [IQR] 41–62). The median number of PT fractions was 31 (IQR 30–39) given over a median duration of 52 days (IQR 44–69). Fourteen patients (7.3%) also received photon radiotherapy and six patients (3.1%) stereotactic radiosurgery. Median follow-up was 4.4 years (IQR 3.86–4.71). Five-year progression-free survival (PFS) rate was 69% (95% confidence interval [CI] 62.1–76.6). For benign, atypical, and malignant meningioma, 5-year PFS rates were 71.5% (95% CI 64.4–79.4), 55.6% (95% CI 32.5–95), and 35.6% (95% CI 12.8–98.9), respectively (p<0.01). In the adjusted regression, tumour location (hazard ratio [HR]=0.1, 95% CI 0.05–0.22, p<0.001), aggressive meningioma (HR=2.26, 95% CI 1.1–4.66, p=0.027), and the need of cerebrospinal fluid (CSF) insertion for hydrocephalus (HR=3.51, 95% CI 1.32–9.31, p=0.012) remained significantly associated to the PFS. All grades considered, 5-year overall survival (OS) rates was 89.7% (95% CI 84.6–95.1). For benign, atypical, and malignant meningioma, 5-year OS rates were 93% (95% CI 88.7–97.4), 76.4% (95% CI 51.4–100), and 44.4% (95% CI 16.7–100), respectively (p<0.01). In the multivariable regression, an older age above 70 years (HR=5.95, 95% CI 2.09–16.89, p<0.001) associated to a high level of comorbidities (HR=5.31, 95% CI 1.43–19.78, p=0.013) and a malignant meningioma (HR=5.68, 95% CI 1.54–20.94, p=0.009) remained significantly associated to a reduced OS.

Conclusion

Five-year PFS and OS after meningioma surgery and PT is favourable but impaired for older patients with high level of morbidities, tumour of the convexity, malignant histopathology and for those requiring CSF shunting. Further inclusion and prolonged follow-up is required to assess other predictors such as sex, tumour volume, or given dose.

The Efficacy and Safety of Carbon Ion Radiotherapy for Meningiomas: A Systematic Review and Meta-Analysis

Objective

The purpose of this systematic review and meta-analysis is to evaluate the efficacy and safety of carbon ion radiotherapy (CI-RT) in improving meningioma by comparing photon and protons radiotherapy.

Methods

A comprehensive search for relevant studies published until March 17, 2021, was conducted in PubMed, the Cochrane Library, Chinese Biomedical Literature Database and EMBASE. Statistical analyses were performed with R 4.0.3.

Results

We identified 396 studies, of which 18 studies involving 985 participants were included. Except for one low quality study, the quality of the included studies was found to be either moderate or high quality. The analyses conducted according random effects model indicated that the 1-year overall survival rate (OS) of benign and non-benign meningiomas after the CI-RT treatment was 99% (95%CL=.91-1.00, I² = 0%). The overall average 5-year OS for meningiomas was 72% (95%CL=0.52-0.86, I² = 35%), not as effective as proton radiotherapy (PR-RT) 85% (95%CL=.72-.93, I² = 73, Q=4.17, df=2, p=.12). Additionally, 5-year OS of atypical meningiomas (81%) was found to be significantly higher than anaplastic meningiomas (52%). The 10-year OS after CI-RT of patients with mixed grade meningioma was 91% (95%CL=.75-.97, I² = 73%). The 15-year OS after CI-RT 87% (95%CL=.11-1.00) or PR-RT 87% (95%CL=.23-.99, I² = 79%) were the same (Q=0, df=1, p=.99). After undergoing CI-RT for 3 and 5 years, the LC for benign meningioma was 100% and 88%, respectively, while the 2-year LC of non-benign meningiomas (atypical/anaplastic) was 33%. Headache, sensory impairment, cognitive impairment, and hearing impairment were found to be the most common adverse reactions, with individual incidences of 19.4%, 23.7%, 9.1%, and 9.1%, respectively.

Conclusion

CI-RT is a rapidly developing technique that has been proven to be an effective treatment against meningioma. The efficacy and safety of CI-RT for meningiomas were similar to those of PR-RT, better than photon radiotherapy (PH-RT). However, there is a need for more prospective trials in the future that can help provide more supportive evidence.

Long-term outcomes of patients with unresectable benign meningioma treated with proton beam therapy

This study aimed to evaluate the long-term efficacy of proton beam therapy (PBT) for unresectable benign meningiomas at the University of Tsukuba, Japan. From 1986-1998, 10 patients were treated at the Particle Radiation Medical Science Center (PRMSC) with a relative biological effectiveness (RBE) value of 1.0 using an accelerator built for physics experiments. The total dose was compensated with an X-ray in three patients. Following that, from 2002-2017, 17 patients were treated with a RBE value of 1.1 at the Proton Medical Research Center (PMRC) which was built for medical use. At the PRMSC, the total dose ranged from 50.4-66 Gy (median: 54 Gy). During the follow-up, which lasted between 3.8 and 31.6 years (median: 25.1 years), the 5-, 10-, 15-, 20- and 30-year local control rates were 100%, and the 5-, 10-, 15-, 20- and 30-year survival rates were 90, 80, 70, 70 and 36%, respectively. One patient died of brainstem radiation necrosis 5.1 years after PBT. At PMRC, the total dose ranged from 45.0-61.2 GyE, with a median of 50.4 GyE. During the follow-up, which lasted between 3 and 17 years with a median of 10.5 years, the 5-, 10- and 15-year local control rates were 94.1%, and the 5-, 10- and 15-year survival rates were 100, 100 and 88.9%, respectively. Neither malignant transformation nor secondary malignancy was observed, indicating that fractionated PBT may be effective and safely control benign unresectable meningioma even for the lifelong period of time.

A Probability-Based Investigation on the Setup Robustness of Pencil-beam Proton Radiation Therapy for Skull-Base Meningioma

Introduction

The intracranial skull-base meningioma is in proximity to multiple critical organs and heterogeneous tissues. Steep dose gradients often result from avoiding critical organs in proton treatment plans. Dose uncertainties arising from setup errors under image-guided radiation therapy are worthy of evaluation.

Patients and Methods

Fourteen patients with skull-base meningioma were retrospectively identified and planned with proton pencil beam scanning (PBS) single-field uniform dose (SFUD) and multifield optimization (MFO) techniques. The setup uncertainties were assigned a probability model on the basis of prior published data. The impact on the dose distribution from nominal 1-mm and large, less probable setup errors, as well as the cumulative effect, was analyzed. The robustness of SFUD and MFO planning techniques in these scenarios was discussed.

Results

The target coverage was reduced and the plan dose hot spot increased by all setup uncertainty scenarios regardless of the planning techniques. For 1 mm nominal shifts, the deviations in clinical target volume (CTV) coverage D99% was -11 ± 52 cGy and -45 ± 147 cGy for SFUD and MFO plans. The setup uncertainties affected the organ at risk (OAR) dose both positively and negatively. The statistical average of the setup uncertainties had <100 cGy impact on the plan qualities for all patients. The cumulative deviations in CTV D95% were 1 ± 34 cGy and -7 ± 18 cGy for SFUD and MFO plans.

Conclusion

It is important to understand the impact of setup uncertainties on skull-base meningioma, as the tumor target has complex shape and is in proximity to multiple critical organs. Our work evaluated the setup uncertainty based on its probability distribution and evaluated the dosimetric consequences. In general, the SFUD plans demonstrated more robustness than the MFO plans in target coverages and brainstem dose. The probability-weighted overall effect on the dose distribution is small compared to the dosimetric shift during single fraction.

Proton Therapy for Intracranial Meningioma for the Treatment of Primary/Recurrent Disease Including Re-Irradiation

Meningeal tumors represent approximately 10-25% of primary brain tumors and occur usually in elderly female patients. Most meningiomas are benign (80-85%) and for symptomatic and/or large tumors, surgery, with or without radiation therapy (RT), has been long established as an effective means of local tumor control. RT can be delivered to inoperable lesions or to those with non-benign histology and for Simpson I-III and IV-V resection. RT can be delivered with photons or particles (protons or carbon ions) in stereotactic or non-stereotactic conditions. Particle therapy delivered for these tumors uses the physical properties of charged carbon ions or protons to spare normal brain tissue (i.e. Bragg peak), with or without or a dose-escalation paradigm for non-benign lesions. PT can substantially decrease the dose delivered to the non-target brain tissues, including but not limited to the hippocampi, optic apparatus or cochlea. Only a limited number of meningioma patients have been treated with PT in the adjuvant or recurrent setting, as well as for inoperable lesions with pencil beam scanning and with protons only. Approximately 500 patients with image-defined or WHO grade I meningioma have been treated with protons. The reported outcome, usually 5-year local tumor control, ranges from 85 to 99% (median, 96%). For WHO grade II or III patients, the outcome of only 97 patients has been published, reporting a median tumor local control rate of 52% (range, 38-71.1). Only 24 recurring patients treated previously with photon radiotherapy and re-treated with PT were reported. The clinical outcome of these challenging patients seems interesting, provided that they presented initially with benign tumors, are not in the elderly category and have been treated previously with conventional radiation dose of photons. Overall, the number of meningioma patients treated or-re-irradiated with this treatment modality is small and the clinical evidence level is somewhat low (i.e. 3b-5). In this review, we detail the results of upfront PT delivered to patients with meningioma in the adjuvant setting and for inoperable tumors. The outcome of meningioma patients treated with this radiation modality for recurrent tumors, with or without previous RT, will also be reviewed.

Moderately Hypofractionated Radiation for Benign Meningiomas and Schwannomas: A Report of 70 Patients Treated Between 2008 and 2018

Purpose

Radiosurgery and fractionated intensity modulated radiation therapy (IMRT) are effective treatment modalities for meningiomas and schwannomas. Although fractionated IMRT yields favorable tumor control, daily treatments for 5 to 6 weeks can be burdensome for patients and health care systems. Thus, hypofractionated radiation may be a reasonable alternative. The purpose of this study was to review the results of patients with benign meningiomas or schwannomas treated at our institution with moderately hypofractionated IMRT.

Methods and Materials

After institutional review board approval, patients treated at a single academic institution between 2008 and 2018 with a primary diagnosis of either meningioma or schwannoma and who received 30 Gy at 3 Gy per fraction were identified. Patient and tumor characteristics, as well as follow-up documentation, were reviewed. Tumor progression was determined by reviewing patient imaging and provider notations.

Results

From 2008 to 2018, 70 patients with either meningioma or schwannoma were treated to 30 Gy. The median patient age was 73 years (range, 43-92 years). At the median follow up of 3.2 years, the local control was 92.9%. Two patients (2.9%) had disease progression, which occurred at 9.6 and 6.6 years after treatment. One patient developed asymptomatic radiographic changes consistent with radiation necrosis, which resolved without intervention. All patients completed the prescribed course without interruption. The mean tumor volume was 18.9 cm³, median volume was 36.6 cm³ (range, 3.4-245.5 cm³), and tumor volume was not associated with recurrence risk. Both tumors with progression were schwannomas.

Conclusions

Hypofractionated radiation with 30 Gy at 3 Gy per fraction is an effective, convenient, and well-tolerated alternative for patients with benign meningiomas or schwannomas. Modest hypofractionation provided durable control for a wide range of tumor volumes and should be considered for patients with a limited life expectancy or those unable to receive a more extended fractionated radiation therapy course.

The Promise of Proton Therapy for Central Nervous System Malignancies

Radiation therapy plays a significant role in management of benign and malignant diseases of the central nervous system. Patients may be at risk of acute and late toxicity from radiation therapy due to dose deposition in critical normal structures. In contrast to conventional photon delivery techniques, proton therapy is characterized by Bragg peak dose deposition which results in decreased exit dose beyond the target and greater sparing of normal structure which may reduce the rate of late toxicities from treatment. Dosimetric studies have demonstrated reduced dose to normal structures using proton therapy as compared to photon therapy. In addition, clinical studies are being reported demonstrating safety, feasibility, and low rates of acute toxicity. Technical challenges in proton therapy remain, including full understanding of depth of proton penetration and the biological activity in the distal Bragg peak. In addition, longer clinical follow-up is required to demonstrate reduction in late toxicities as compared to conventional photon-based radiation techniques. In this review, we summarize the current clinical literature and areas of active investigation in proton therapy for adult central nervous system malignancies.

Dosimetric comparisons of different hypofractionated stereotactic radiotherapy techniques in treating intracranial tumors > 3 cm in longest diameter

OBJECTIVE

The authors sought to compare the dosimetric quality of hypofractionated stereotactic radiosurgery in treating sizeable brain tumors across the following treatment platforms: GammaKnife (GK) Icon, CyberKnife (CK) G4, volumetric modulated arc therapy (VMAT) on the Varian TrueBeam STx, double scattering proton therapy (DSPT) on the Mevion S250, and intensity modulated proton therapy (IMPT) on the Varian ProBeam.

METHODS

In this retrospective study, stereotactic radiotherapy treatment plans were generated for 10 patients with sizeable brain tumors (> 3 cm in longest diameter) who had been treated with VMAT. Six treatment plans, 20-30 Gy in 5 fractions, were generated for each patient using the same constraints for each of the following radiosurgical methods: 1) GK, 2) CK, 3) coplanar arc VMAT (VMAT-C), 4) noncoplanar arc VMAT (VMAT-NC), 5) DSPT, and 6) IMPT. The coverage; conformity index; gradient index (GI); homogeneity index; mean and maximum point dose of organs at risk; total dose volume (V) in Gy to the normal brain for 2 Gy (V2), 5 Gy (V5), and 12 Gy (V12); and integral dose were compared across all platforms.

RESULTS

Among the 6 techniques, GK consistently produced a sharper dose falloff despite a greater central target dose. GK gave the lowest GI, with a mean of 2.7 ± 0.1, followed by CK (2.9 ± 0.1), VMAT-NC (3.1 ± 0.3), and VMAT-C (3.5 ± 0.3). The highest mean GIs for the proton beam treatments were 3.8 ± 0.4 for DSPT and 3.9 ± 0.4 for IMPT. The GK consistently targeted the lowest normal brain volume, delivering 5 to 12 Gy when treating relatively smaller- to intermediate-sized lesions (less than 15-20 cm3). Yet, the differences across the 6 modalities relative to GK decreased with the increase of target volume. In particular, the proton treatments delivered the lowest V5 to the normal brain when the target size was over 15-20 cm3 and also produced the lowest integral dose to the normal brain regardless of the target size.

CONCLUSIONS

This study provides an insightful understanding of dosimetric quality from both photon and proton treatment across the most advanced stereotactic radiotherapy platforms.

[Treatment of petroclival meningiomas: current state of the problem]

Petroclival meningiomas (PCMs) are benign, slowly growing tumors. Surgery still remains the main treatment option for them. The desire for total resection of large extended PCMs often leads to the development or worsening of persistent neurological deficits. This paper presents a review of the world literature devoted to petroclival meningiomas. We discuss the issues of PCM classification, biology, diagnosis, and selection of the optimal algorithm for their treatment.

The Role of Particle Therapy for the Treatment of Skull Base Tumors and Tumors of the Central Nervous System (CNS)

Radiation therapy (RT) is a mainstay in the interdisciplinary treatment of brain tumors of the skull base and brain. Technical innovations during the past 2 decades have allowed for increasingly precise treatment with better sparing of adjacent healthy tissues to prevent treatment-related side effects that influence patients' quality of life. Particle therapy with protons and charged ions offer favorable kinetics with sharp dose deposition in a well-defined depth (Bragg-Peak) and a steep radiation fall-off beyond that maximum. This review highlights the role of particle therapy in the management of primary brain tumors and tumors of the skull base.

Effects of Surgery and Radiotherapy on Recurrent Skull Base Meningiomas: Clinical and Biological Analyses

We reviewed the medical records of 392 patients who underwent initial surgery for skull base meningiomas between 1983 and 2008. Among them, 32 (8.2%) showed tumor recurrence. Risk factors for recurrence were analyzed clinically and biologically. Recurrent cases were treated with radiotherapy, surgery, or both. In reoperation cases, pathological and biological changes were analyzed and compared between groups with or without radiotherapy. The recurrence rate was statistically high in cases of partial tumor removal and in patients with tumor in the cavernous sinus, tumors with histological WHO (World Health Organization) grade ≥ II or MIB-1 index > 3. The local control rate of postoperative radiotherapy for recurrent cases was 66.7%. Malignant transformation and MIB-1 index elevation was observed more frequently in patients who underwent reoperation after radiotherapy than in the reoperation-only group. Risk factors for recurrence of skull base meningiomas are as follows: (1) partial tumor removal, (2) tumor in the cavernous sinus, (3) histological WHO grade ≥ II, or (4) MIB-1 index > 3. Postoperative radiotherapy might be effective for tumor recurrence. However, the indications for radiotherapy should be carefully considered because postsurgical radiotherapy may increase biological activity, inducing malignant transformation.

Proton therapy for treatment of intracranial benign tumors in adults: A systematic review

INTRODUCTION

The depth-dose distribution of a proton beam, materialized by the Bragg peak makes it an attractive radiation modality as it reduces exposure of healthy tissues to radiations, compared with photon therapy Prominent indications, based on a long-standing experience are: intraocular melanomas, low-grade skull-base and spinal canal malignancies. However, many others potential indications are under investigations such as the benign morbid conditions that are compatible with an extended life-expectancy: low grade meningiomas, paragangliomas, pituitary adenomas, neurinomas craniopharyngioma or recurrent pleomorphic adenomas.

MATERIALS

Given the radiation-induced risk of secondary cancer and the potential neurocognitive and functional alteration with photonic radiotherapy, we systematically analyzed the existing clinical literature about the use of proton therapy as an irradiation modality for cervical or intracranial benign tumors. The aim of this review was to report clinical outcomes of adult patients with benign intracranial or cervical tumors treated with proton therapy and to discuss about potential advantages of proton therapy over intensity modulated radiotherapy or radiosurgery.

RESULTS

Twenty-four studies were included. There was no randomized studies. Most studies dealt with low grade meningiomas (n = 9). Studies concerning neurinoma (n = 4), pituitary adenoma (n = 5), paraganglioma (n = 5), or craniopharyngioma (n = 1) were fewer. Whatever the indication, long term local control was systematically higher than 90% and equivalent to series with conventional radiotherapy.

CONCLUSION

Proton-therapy for treatment of adult benign intracranial and cervical tumors is safe. Randomized or prospective cohorts with long term cognitive evaluations are needed to assess the real place of proton-therapy in the treatment of adults benign head and neck tumors.

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.

Overall survival benefit associated with adjuvant radiotherapy in WHO grade II meningioma

Background

Adjuvant radiotherapy (RT) after surgical resection of World Health Organization (WHO) grade II meningioma, also known as atypical meningioma (AM), is a topic of controversy. The purpose of this study is to compare overall survival (OS) with or without adjuvant RT after subtotal resection (STR) or gross total resection (GTR) in AM patients diagnosed according to the 2007 WHO classification.

Methods

The National Cancer Database was used to identify 2515 patients who were diagnosed with AM between 2009 and 2012 and underwent STR or GTR with or without adjuvant RT. Propensity score matching was first applied to balance covariates including age, year of diagnosis, sex, race, histology, and tumor size in STR or GTR cohorts stratified by adjuvant RT status. Multivariate regression according to the Cox proportional hazards model and Kaplan-Meier survival plots with log-rank test were then used to evaluate OS difference associated with adjuvant RT.

Results

GTR is associated with improved OS compared with STR. In the subgroup analysis, adjuvant RT in patients who underwent STR demonstrated significant association with improved OS compared with no adjuvant RT (adjusted hazard ratio [AHR] 0.590, P = .045); however, adjuvant RT is not associated with improved OS in patients who underwent GTR (AHR 1.093, P = .737).

Conclusions

Despite the lack of consensus on whether adjuvant RT reduces recurrence after surgical resection of AM, our study observed significantly improved OS with adjuvant RT compared with no adjuvant RT after STR.

Clinical outcome after particle therapy for meningiomas of the skull base: toxicity and local control in patients treated with active rasterscanning

BACKGROUND

Meningiomas of the skull base account for 25-30% of all meningiomas. Due to the complex structure of the cranial base and its close proximity to critical structures, surgery is often associated with substantial morbidity. Treatment options include observation, aggressive surgical intervention, stereotactic or conventional radiotherapy. In this analysis we evaluate the outcome of 110 patients with meningiomas of the skull base treated with particle therapy. It was performed within the framework of the "clinical research group heavy ion therapy" and supported by the German Research Council (DFG, KFO 214).

METHODS

Between May 2010 and November 2014, 110 Patients with skull base meningioma were treated with particle radiotherapy at the Heidelberg Ion Therapy Center (HIT). Primary localizations included the sphenoid wing (n = 42), petroclival region (n = 23), cavernous sinus (n = 4), sella (n = 10) and olfactory nerve (n = 4). Sixty meningiomas were benign (WHO °I); whereas 8 were high-risk (WHO °II (n = 7) and °III (n = 1)). In 42 cases histology was not examined, since no surgery was performed. Proton (n = 104) or carbon ion (n = 6) radiotherapy was applied at Heidelberg Ion Therapy Center (HIT) using raster-scanning technique for active beam delivery. Fifty one patients (46.4%) received radiotherapy due to tumor progression, 17 (15.5%) after surgical resection and 42 (38.2%) as primary treatment.

RESULTS

Median follow-up in this analysis was 46,8 months (95% CI 39,9-53,7; Q1-Q3 34,3-61,7). Particle radiotherapy could be performed safely without toxicity-related interruptions. No grade IV or V toxicities according to CTCAE v4.0 were observed. Particle RT offered excellent overall local control rates with 100% progression-free survival (PFS) after 36 months and 96.6% after 60 months. Median PFS was not reached due to the small number of events. Histology significantly impacted PFS with superior PFS after 5 years for low-risk tumors (96.6% vs. 75.0%, p = 0,02). Overall survival was 96.2% after 60 months and 92.0% after 72 months from therapy. Of six documented deaths, five were definitely not and the sixth probably not meningioma-related.

CONCLUSION

Particle radiotherapy is an excellent treatment option for patients with meningiomas of the skull base and can lead to long-term tumor control with minimal side effects. Other prospective studies with longer follow-up will be necessary to further confirm the role of particle radiotherapy in skull base meningioma.

Impact of radiotherapy in atypical meningioma recurrence: literature review

Evaluate whether radiotherapy (RT) after the neurosurgical treatment of atypical meningiomas (AM) has an impact on the reduction rate of recurrence. A Medline search through October 2017 using "atypical meningioma" returned 1277 papers for initial review. Inclusion criteria were as follows. We analyzed the database and included articles in which the anatomic pathological classification of atypical meningiomas was in accordance with WHO 2007 or WHO 2016 criteria, patients > 18 years of age, and there was postoperative external beam radiation to the tumor bed. Exclusion criteria were WHO grade I or III meningioma, patients who underwent whole-brain radiation, RT used as salvage therapy for recurrence, palliative dose of RT (< 45 Gy), recurrent AMs, and multiple AMs. Papers reporting outcomes in which atypical and anaplastic meningiomas were analyzed together were rejected, as were papers with small samples that may compromise evaluation. After filtering our initial selection, only 17 papers were selected. After reviewing the seventeen articles including a total of 1761 patients (972 female and 799 male; 1.21 female/1.0 male), the difference in proportion of tumor recurrence between patients with and without radiotherapy after neurosurgical procedure was 1.0448, 95% CI [0.8318 to 1.3125], p value = 0.7062. On the basis of this review, there is no evidence to suggest that RT decreases the rate of recurrence in patients with atypical meningiomas.

Proton and helium ion radiotherapy for meningioma tumors: a Monte Carlo-based treatment planning comparison

BACKGROUND

Due to their favorable physical and biological properties, helium ion beams are increasingly considered a promising alternative to proton beams for radiation therapy. Hence, this work aims at comparing in-silico the treatment of brain and ocular meningiomas with protons and helium ions, using for the first time a dedicated Monte Carlo (MC) based treatment planning engine (MCTP) thoroughly validated both in terms of physical and biological models.

METHODS

Starting from clinical treatment plans of four patients undergoing proton therapy with a fixed relative biological effectiveness (RBE) of 1.1 and a fraction dose of 1.8 Gy(RBE), new treatment plans were optimized with MCTP for both protons (with variable and fixed RBE) and helium ions (with variable RBE) under the same constraints derived from the initial clinical plans. The resulting dose distributions were dosimetrically compared in terms of dose volume histograms (DVH) parameters for the planning target volume (PTV) and the organs at risk (OARs), as well as dose difference maps.

RESULTS

In most of the cases helium ion plans provided a similar PTV coverage as protons with a consistent trend of superior OAR sparing. The latter finding was attributed to the ability of helium ions to offer sharper distal and lateral dose fall-offs, as well as a more favorable differential RBE variation in target and normal tissue.

CONCLUSIONS

Although more studies are needed to investigate the clinical potential of helium ions for different tumour entities, the results of this work based on an experimentally validated MC engine support the promise of this modality with state-of-the-art pencil beam scanning delivery, especially in case of tumours growing in close proximity of multiple OARs such as meningiomas.

Hypofractionated high-energy proton-beam irradiation is an alternative treatment for WHO grade I meningiomas

Background

Radiation treatment is commonly employed in the treatment of meningiomas. The aim of this study was to evaluate the effectiveness and safety of hypofractionated high-energy proton therapy as adjuvant or primary treatment for WHO grade I meningiomas.

Method

A total of 170 patients who received irradiation with protons for grade I meningiomas between 1994 and 2007 were included in the study. The majority of the tumours were located at the skull base (n = 155). Eighty-four patients were treated post subtotal resection, 42 at tumour relapse and 44 with upfront radiotherapy after diagnosis based on the typical radiological image. Irradiation was given in a hypofractionated fashion (3–8 fractions, usually 5 or 6 Gy) with a mean dose of 21.9 Gy (range, 14–46 Gy). All patients were planned for follow-up with clinical controls and magnetic resonance imaging scans at 6 months and 1, 2, 3, 5, 7 and 10 years after treatment. The median follow-up time was 84 months. Age, gender, tumour location, Simpson resection grade and target volume were assessed as possible prognostic factors for post-irradiation tumour progression and radiation related complications.

Results

The actuarial 5- and 10-year progression-free survival rates were 93% and 85% respectively. Overall mortality rate was 13.5%, while disease-specific mortality was 1.7% (3/170 patients). Older patients and patients with tumours located in the middle cranial fossa had a lower risk for tumour progression. Radiation-related complications were seen in 16 patients (9.4%), with pituitary insufficiency being the most common. Tumour location in the anterior cranial fossa was the only factor that significantly increased the risk of complications.

Conclusions

Hypofractionated proton-beam radiation therapy may be used particularly in the treatment of larger World Health Organisation grade I meningiomas not amenable to total surgical resection. Treatment is associated with high rates of long-term tumour growth control and acceptable risk for complications.

Treatment of meningioma and glioma with protons and carbon ions

The rapid rise of particle therapy across the world necessitates evidence to justify its ever-increasing utilization. This narrative review summarizes the current status of these technologies on treatment of both meningiomas and gliomas, the most common benign and malignant primary brain tumors, respectively. Proton beam therapy (PBT) for meningiomas displays high rates of long-term local control, low rates of symptomatic deterioration, along with the potential for safe dose-escalation in select (but not necessarily routine) cases. PBT is also associated with low adverse events and maintenance of functional outcomes, which have implications for quality of life and cost-effectiveness measures going forward. Data on carbon ion radiation therapy (CIRT) are limited; existing series describe virtually no high-grade toxicities and high local control. Regarding the few available data on low-grade gliomas, PBT provides opportunities to dose-escalate while affording no increase of severe toxicities, along with maintaining appropriate quality of life. Although dose-escalation for low-grade disease has been less frequently performed than for glioblastoma, PBT and CIRT continue to be utilized for the latter, and also have potential for safer re-irradiation of high-grade gliomas. For both neoplasms, the impact of superior dosimetric profiles with endpoints such as neurocognitive decline and neurologic funcionality, are also discussed to the extent of requiring more data to support the utility of particle therapy. Caveats to these data are also described, such as the largely retrospective nature of the available studies, patient selection, and heterogeneity in patient population as well as treatment (including mixed photon/particle treatment). Nevertheless, multiple prospective trials (which may partially attenuate those concerns) are also discussed. In light of the low quantity and quality of available data, major questions remain regarding economic concerns as well.

Long-Term Clinical Outcomes of Pencil Beam Scanning Proton Therapy for Benign and Non-benign Intracranial Meningiomas

PURPOSE

To assess and report long-term clinical outcomes regarding local control, overall survival, and toxicity-free survival after pencil beam scanning proton therapy for intracranial meningiomas at a single institution.

PATIENTS AND METHODS

Ninety-six patients (male/female, 29/67; median age 52.8 years) with intracranial meningiomas (World Health Organization [WHO] grade 1, n=61 [63.5%]; WHO grade 2, n=33 [34.4%]; WHO grade 3, n=2 [2.1%]) were treated with pencil beam scanning proton therapy (n=53 [55.2%] at diagnosis, n=17 [17.7%] at recurrence, and n=26 [27.1%] for tumor progression). Median gross tumor volume before PBSPT was 21.4 cm³ (range, 0.0-546.5 cm³), with a median planning target volume of 123.4 cm³ (range, 4.6-1142.0 cm³). Median duration of follow-up was 56.9 months (range, 12.1-207.2 months). Late toxicity was graded according to the Common Terminology Criteria for Adverse Events, version 4.0.

RESULTS

Thirteen failures (14%) (male/female, 6/7) were observed, of which the majority (n=9, 69%) were of non-benign histology. The 5-year actuarial local control and overall survival were 86.4% and 88.2%, respectively. Five-year grade ≥3 toxicity-free survival was 89.1%. On univariate analysis, local control was worse for patients with higher WHO grade (P≤.001), those treated after at least 1 recurrence (P=.006), those with non-skull base tumor location (P=.014), and males (P=.032). Significant prognosticators for 5-year overall survival were local control (P≤.001), age (P=.002), and timing of proton therapy (initial vs recurrence) (P=.002).

CONCLUSIONS

Pencil beam scanning proton therapy is an effective and safe treatment for patients with intracranial meningiomas, resulting in high local control rates with limited toxicity. Up-front radiation likely results in improved outcomes and should be considered, especially for patients with non-benign tumors and/or for those with incomplete resections.

Does Proton Therapy Have a Future in CNS Tumors?

OPINION STATEMENT

Proton therapy is characterized by certain physical properties leading to a reduction in integral dose. As proton therapy becomes more widely available, the ongoing discussion on the real indications for proton therapy becomes more important. In the present article, data on proton therapy for tumors of the central nervous system (CNS) is summarized and discussed in view of modern photon treatments. Still today, no randomized controlled trials are available confirming any clinical benefit of protons in CNS tumors. For certain skull base lesions, such as chordomas and chondrosarcomas, dose escalation is possible with protons thus patients should be referred to a proton center if readily available. For vestibular schwannoma, at present, proton data are inferior to advanced photons. For glioma patients, early data is present for low-grade gliomas, presenting comparable results to photons; dose escalation studies for high-grade gliomas have led to significant side effects, thus strategies of dose-escalation need to rethought. For skull base meningiomas, data from stereotactic series and IMRT present excellent local control with minimal side effects, thus any improvement with protons might only be marginal. The largest benefit is considered in pediatric CNS tumors, due to the intricate radiation sensitivity of children's normal tissue, as well as the potential of long-term survivorship. Long-term data is still lacking, and even recent analyses do not all lead to a clear reduction in side effects with improvement of outcome; furthermore, clinical data seem to be comparable. However, based on the preclinical evidence, proton therapy should be evaluated in every pediatric patient. Protons most likely have a benefit in terms of reduction of long-term side effects, such as neurocognitive sequelae or secondary malignancies; moreover, dose escalation can be performed in radio-resistant histologies. Clinical data with long-term follow-up is still warranted to prove any superiority to advanced photons in CNS tumors. If available, protons should be evaluated for chordoma or chondrosarcoma of the skull base and pediatric tumors. However, many factors are important for excellent oncology care, and no time delay or inferior oncological care should be accepted for the sake of protons only.

Review of photon and proton radiotherapy for skull base tumours

An extremely large variety of benign and malignant tumours occur at skull base; these tumour lesions are in the proximity to structures deputed to relevant physiologic functions, limiting extensive surgical approaches to this body district. Most recent progresses of surgery and radiotherapy have allowed to improve local control with acceptable rates of side effects. Various photon radiotherapy techniques are employed, including 3-dimensional conformal radiotherapy, intensity modulated radiotherapy (IMRT), stereotactic radiotherapy (SRT) and brachytherapy that is manly limited to the treatment of primary or recurrent nasopharyngeal carcinoma. Proton beam radiotherapy is also extensively used thanks to its physical characteristics. Our review, focusing in particular on meningioma, chordoma, and chondrosarcoma, suggests that proton therapy plays a major role in the treatment of malignant tumours whereas photon therapy still plays a relevant role in the treatment of benign tumour lesions.

Long-term evaluation of the effect of hypofractionated high-energy proton treatment of benign meningiomas by means of (11)C-L-methionine positron emission tomography

PURPOSE

To determine if (11)C-L-methionine PET is a useful tool in the evaluation of the long-term effect of proton beam treatment in patients with meningioma remnant.

METHODS

Included in the study were 19 patients (4 men, 15 women) with intracranial meningioma remnants who received hypofractionated high-energy proton beam treatment. Patients were examined with (11)C-L-methionine PET and MRI prior to treatment and after 6 months, and 1, 2, 3, 5, 7 and 10 years. Temporal changes in methionine uptake ratio, meningioma volume, meningioma regrowth and clinical symptoms throughout the follow-up period were evaluated.

RESULTS

In 17 patients the tumour volume was unchanged throughout the follow-up. The methionine uptake ratio on PET decreased over the years in most patients. In two patients the tumour remnant showed progression on MRI. In these patients, prior to the volume increase on MRI, the methionine uptake ratio increased. One patient experienced transient clinical symptoms and showed radiological evidence of a radiation-induced reaction close to the irradiated field.

CONCLUSION

Proton beam treatment is a safe and effective treatment for achieving long-term growth arrest in meningioma remnants. Follow-up with (11)C-L-methionine PET may be a valuable adjunct to, but not a replacement for, standard radiological follow-up.

Stereotactic radiosurgery for intracranial meningiomas: current concepts and future perspectives

Meningiomas are among the most common adult brain tumors. Although the optimal management of meningiomas would provide complete elimination of the lesion, this cannot always be accomplished safely through resection. Therefore, other therapeutic modalities, such as stereotactic radiosurgery (as primary or adjunctive therapy), have emerged. In the current review, we have provided an overview of the historical outcomes of various radiosurgical modalities applied in the management of meningiomas. Furthermore, we provide a discussion on key factors (eg World Health Organization grade, lesion size, and lesion location) that affect tumor control and adverse event rates. We discuss recent changes in our understanding of meningiomas, based on molecular and genetic markers, and how these will change our perspective on the management of meningiomas. We conclude by outlining the areas in which knowledge gaps persist and provide suggestions as to how these can be addressed.

Hypofractionated stereotactic radiation therapy in skull base meningiomas

To investigate the role of hypo-fractionated stereotactic radiation treatment (HSRT) in the management of skull base meningioma. Twenty-six patients were included in the study and treated with a dose of 30 Gy in 5 fractions with volumetric modulated arc therapy (RapidArc). Eighteen patients were symptomatic before treatment. Endpoints were local toxicity and relief from symptoms. Tumors were located in anterior skull base in 4/27 cases, in middle skull base in 12/27 and in posterior skull base in 11/27. HSRT was performed as first treatment in 17 (65 %) patients, in 9 (35 %) patients it followed a previous partial resection. Median follow up was 24.5 months (range 5-57 months). clinical remission of symptoms, complete or partial, was obtained in the vast majority of patients after treatment. Out of the 18 symptomatic patients, partial remission occurred in 9 (50 %) patients and complete remission in 9 (50 %). All asymptomatic patients retained their status after treatment. No severe neurologic toxicity grade III-IV was recorded. No increase of meningioma in the same site of treatment occurred; 16 (62 %) patients had stable disease and 9 (38 %) patients had tumor reduction. The mean tumor volume after treatment was 10.8 ± 17.8 cm(3) compared with 13.0 ± 19.1 cm(3) before treatment (p = 0.02). The mean actuarial OS was 54.4 ± 2.8 months. The 1- and 2-years OS was 92.9 ± 0.7 %. HSRT proved to be feasible for these patients not eligible to full surgery or to ablative radiation therapy. Local control and durability of results suggest for a routine application of this approach in properly selected cases.

Meningiomas: knowledge base, treatment outcomes, and uncertainties. A RANO review

Evolving interest in meningioma, the most common primary brain tumor, has refined contemporary management of these tumors. Problematic, however, is the paucity of prospective clinical trials that provide an evidence-based algorithm for managing meningioma. This review summarizes the published literature regarding the treatment of newly diagnosed and recurrent meningioma, with an emphasis on outcomes stratified by WHO tumor grade. Specifically, this review focuses on patient outcomes following treatment (either adjuvant or at recurrence) with surgery or radiation therapy inclusive of radiosurgery and fractionated radiation therapy. Phase II trials for patients with meningioma have recently completed accrual within the Radiation Therapy Oncology Group and the European Organisation for Research and Treatment of Cancer consortia, and Phase III studies are being developed. However, at present, there are no completed prospective, randomized trials assessing the role of either surgery or radiation therapy. Successful completion of future studies will require a multidisciplinary effort, dissemination of the current knowledge base, improved implementation of WHO grading criteria, standardization of response criteria and other outcome end points, and concerted efforts to address weaknesses in present treatment paradigms, particularly for patients with progressive or recurrent low-grade meningioma or with high-grade meningioma. In parallel efforts, Response Assessment in Neuro-Oncology (RANO) subcommittees are developing a paper on systemic therapies for meningioma and a separate article proposing standardized end point and response criteria for meningioma.

Stereotactic radiation therapy for skull base recurrences: Is a salvage approach still possible?

AIM

A literature review was performed to analyse the role of stereotactic radiotherapy given in a single shot or in a fractionated fashion for recurrent skull base tumours in order to ascertain if it can be a real salvage approach.

BACKGROUND

The management of recurrent skull base tumours can have a curative or palliative intent and mainly includes surgery and RT.

MATERIALS AND METHODS

One-thousand-ninety-one articles were found in the search databases and the most relevant of them were analysed and briefly described.

RESULTS

Data on recurrences of meningioma, pituitary adenoma, craniopharyngioma, chordoma and chondrosarcoma, vestibular schwannoma, glomus jugulare tumours, olfactory neuroblastoma and recurrences from head and neck tumours invading the base of skull are reported highlighting the most relevant results in terms of local control, survival, side effects and complications.

CONCLUSIONS

In conclusion, it emerges that SRS and FSRT are effective and safe radiation modalities of realize real salvage treatment for recurrent skull base tumours.

Controversies in radiotherapy for meningioma

Meningiomas are the most common primary intracranial tumour. Although external beam radiotherapy and radiosurgery are well-established treatments, affording local control rates of 85-95% at 10 years, the evidence base is mainly limited to single institution case series. This has resulted in inconsistent practices. It is generally agreed that radiotherapy is an established primary therapy in patients requiring treatment for surgically inaccessible disease and postoperatively for grade 3 tumours. Controversy exists surrounding whether radiotherapy should be upfront or reserved for progression for incompletely excised and grade 2 tumours. External beam radiotherapy and radiosurgery have not been directly compared, but seem to offer comparable rates of control for benign disease. Target volume definition remains contentious, including the inclusion of hyperostotic bone, dural tail and surrounding brain, but pathological studies are shedding some light. Most agree that doses around 50-54 Gy are appropriate for benign meningiomas and ongoing European Organization for Research and Treatment of Cancer and Radiation Therapy Oncology Group studies are evaluating dose escalation for higher risk disease. Here we address the 'who, when and how' of radiotherapy for meningioma.

Prospective evaluation of early treatment outcome in patients with meningiomas treated with particle therapy based on target volume definition with MRI and 68Ga-DOTATOC-PET

PURPOSE

To evaluate early treatment results and toxicity in patients with meningiomas treated with particle therapy.

MATERIAL AND METHODS

Seventy patients with meningiomas were treated with protons (n = 38) or carbon ion radiotherapy (n = 26). Median age was 49 years. Median age at treatment was 55 years, 24 were male (34%), and 46 were female (66%). Histology was benign meningioma in 26 patients (37%), atypical in 23 patients (33%) and anaplastic in four patients (6%). In 17 patients (24%) with skull base meningiomas diagnosis was based on the typical appearance of a meningioma. For benign meningiomas, total doses of 52.2-57.6 GyE were applied with protons. For high-grade lesions, the boost volume was 18 GyE carbon ions, with a median dose of 50 GyE applied as highly conformal radiation therapy. Nineteen patients were treated as re-irradiation. Treatment planning with MRI and 68-Ga-DOTATOC-PET was evaluated.

RESULTS

Very low rates of side effects developed, including headaches, nausea and dizziness. No severe treatment-related toxicity was observed. Local control for benign meningiomas was 100%. Five of 27 patients (19%) developed tumor recurrence during follow-up. Of these, four patients had been treated as re-irradiation for recurrent high-risk meningiomas. Actuarial local control after re-irradiation of high-risk meningiomas was therefore 67% at six and 12 months. In patients treated with primary radiotherapy, only one of 13 patients (8%) developed tumor recurrence 17 months after radiation therapy (photon and carbon ion boost).

CONCLUSION

Continuous prospective follow-up and development of novel study concepts are required to fully exploit the long-term clinical data after particle therapy for meningiomas. To date, it may be concluded that when proton therapy is available, meningioma patients can be offered a treatment at least comparable to high-end photon therapy.

State-of-the-art treatment alternatives for base of skull meningiomas: complementing and controversial indications for neurosurgery, stereotactic and robotic based radiosurgery or modern fractionated radiation techniques

For skull base meningiomas, several treatment paradigms are available: Observation with serial imaging, surgical resection, stereotactic radiosurgery, radiation therapy or some combination of both. The choice depends on several factors. In this review we evaluate different treatment options, the outcome of modern irradiation techniques as well as the clinical results available, and establish recommendations for the treatment of patients with skull-base meningiomas.

Radiosurgery with photons or protons for benign and malignant tumours of the skull base: a review

Stereotactic radiosurgery (SRS) is an important treatment option for intracranial lesions. Many studies have shown the effectiveness of photon-SRS for the treatment of skull base (SB) tumours; however, limited data are available for proton-SRS.Several photon-SRS techniques, including Gamma Knife, modified linear accelerators (Linac) and CyberKnife, have been developed and several studies have compared treatment plan characteristics between protons and photons.The principles of classical radiobiology are similar for protons and photons even though they differ in terms of physical properties and interaction with matter resulting in different dose distributions.Protons have special characteristics that allow normal tissues to be spared better than with the use of photons, although their potential clinical superiority remains to be demonstrated.A critical analysis of the fundamental radiobiological principles, dosimetric characteristics, clinical results, and toxicity of proton- and photon-SRS for SB tumours is provided and discussed with an attempt of defining the advantages and limits of each radiosurgical technique.

Fractionated proton radiotherapy for benign cavernous sinus meningiomas

PURPOSE

To evaluate the efficacy of fractionated proton radiotherapy for a population of patients with benign cavernous sinus meningiomas.

METHODS AND MATERIALS

Between 1991 and 2002, 72 patients were treated at Loma Linda University Medical Center with proton therapy for cavernous sinus meningiomas. Fifty-one patients had biopsy or subtotal resection; 47 had World Health Organization grade 1 pathology. Twenty-one patients had no histologic verification. Twenty-two patients received primary proton therapy; 30 had 1 previous surgery; 20 had more than 1 surgery. The mean gross tumor volume was 27.6 cm(3); mean clinical target volume was 52.9 cm(3). Median total doses for patients with and without histologic verification were 59 and 57 Gy, respectively. Mean and median follow-up periods were 74 months.

RESULTS

The overall 5-year actuarial control rate was 96%; the control rate was 99% in patients with grade 1 or absent histologic findings and 50% for those with atypical histology. All 21 patients who did not have histologic verification and 46 of 47 patients with histologic confirmation of grade 1 tumor demonstrated disease control at 5 years. Control rates for patients without previous surgery, 1 surgery, and 2 or more surgeries were 95%, 96%, and 95%, respectively.

CONCLUSIONS

Fractionated proton radiotherapy for grade 1 cavernous sinus meningiomas achieves excellent control rates with minimal toxicities, regardless of surgical intervention or use of histologic diagnosis. Disease control for large lesions can be achieved by primary fractionated proton therapy.