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

Quality of life in patients with skull base meningiomas treated with microsurgery: a prospective observational study

BACKGROUND

Skull base meningiomas are chronic conditions that can present with a wide variety of symptoms ranging from near normalcy to chronic and prolonged disability and also often worsen by treatment-related sequelae. Hence, it is necessary to investigate the quality of life (QOL) among patients with skull base meningioma and evaluate the impact of microsurgery on their overall well-being.

METHODS

In this prospective observational study, 36 patients undergoing microsurgery for skull base meningioma were assessed for QOL using SF-36 questionnaires. Results were compared to the QOL of 36 patients with a non-neurosurgical chronic disease (diabetes mellitus) and 36 matched healthy volunteers. This study commenced from 2019 and ended in 2022.

RESULTS

All QOL parameters in skull base meningioma patients were preoperatively significantly worse than in the healthy population. The most affected QOL domain were role limitation due to physical health (RLPH) and role limitation due to emotional problems (RLEP). Within one year after surgery, skull base meningioma patients showed a significant improvement of all QOL parameters. The domains of physical functioning (PF), emotional well-being (EWB), body pain (BP) and general health (GH) improved to similar values as their matched healthy controls. However, social functioning (SF), RLPH, and RLPE remained still significantly affected. Compared to chronic diabetic patients, the domains PF, EWB, BP, and GH showed significantly better QOL values after one year in skull base meningioma patients, but RLEP and RLPH were worse.

CONCLUSION

Microsurgery can significantly improve all QOL domains in skull base meningioma patients within one year. Physical activity, overall health, and mental well-being have been observed to return to even normal levels. While certain QOL domains may still be affected post-microsurgery, it is evident that microsurgery can yield a substantial improvement, ultimately raising QOL to levels surpassing those seen in other non-neurosurgical chronic diseases, such as diabetes mellitus.

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.

Comprehensive assessment of proton plans with three different beam delivery systems for multiple brain metastases

Purpose

To compare plan quality among photon volumetric arc therapy (VMAT), Gamma Knife, and three different proton beam modalities.

Methods

Fifty-five brain lesions from 20 patients were planned with three different proton spot size ranges of cyclotron-generated proton beams, CPBs (spot size σ: 2.7-7.0 mm), linear accelerator proton beams, LPBs (σ: 2.9-5.5 mm), and linear accelerator proton minibeams, LPMBs (σ: 0.9-3.9 mm), with and without apertures and compared against photon VMAT and Gamma Knife plans. Dose coverage to each lesion for each proton and photon plan was set to 99% of the GTV receiving the prescription (Rx) dose. All proton plans used ±2 mm setup uncertainty and ±2% range uncertainty in robust evaluation to achieve V100%Rx > 95% of the GTV. Apertures were applied to proton beams irradiating tumors <1 cm3 volume and located <2.5 cm depth. Conformity index (CI), gradient index (GI), V12 Gy, V4.5 Gy, and mean brain dose were compared across all plan types. The Wilcoxon signed rank test was utilized to determine statistical significance of dosimetric results compared between photon and proton plans.

Results

When compared to CPB generated plans, average CI and GI were significantly better for the LPB and LPMB plans. Aperture-based IMPT plans showed improvement from Gamma Knife for all dosimetric metrics. Aperture-based IMPT plans also showed improvement in all dosimetric metrics for shallow tumors (d < 2.5 cm) when compared with non-aperture-based plans.

Conclusion

The LPB and LPMB stand as excellent alternatives to CPB or photon therapy and significantly increase the preservation of normal tissue.

The evolving role of reirradiation in the management of recurrent brain tumors

Despite aggressive management consisting of surgery, radiation therapy (RT), and systemic therapy given alone or in combination, a significant proportion of patients with brain tumors will experience tumor recurrence. For these patients, no standard of care exists and management of either primary or metastatic recurrent tumors remains challenging.Advances in imaging and RT technology have enabled more precise tumor localization and dose delivery, leading to a reduction in the volume of health brain tissue exposed to high radiation doses. Radiation techniques have evolved from three-dimensional (3-D) conformal RT to the development of sophisticated techniques, including intensity modulated radiation therapy (IMRT), volumetric arc therapy (VMAT), and stereotactic techniques, either stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT). Several studies have suggested that a second course of RT is a feasible treatment option in patients with a recurrent tumor; however, survival benefit and treatment related toxicity of reirradiation, given alone or in combination with other focal or systemic therapies, remain a controversial issue.We provide a critical overview of the current clinical status and technical challenges of reirradiation in patients with both recurrent primary brain tumors, such as gliomas, ependymomas, medulloblastomas, and meningiomas, and brain metastases. Relevant clinical questions such as the appropriate radiation technique and patient selection, the optimal radiation dose and fractionation, tolerance of the brain to a second course of RT, and the risk of adverse radiation effects have been critically discussed.

Long-Term Outcomes after Multimodal Treatment for Clival Chordoma: Efficacy of the Endonasal Transclival Approach with Early Adjuvant Radiation Therapy

This study investigates the long-term outcomes of clival chordoma patients treated with the endonasal transclival approach (ETCA) and early adjuvant radiation therapy. A retrospective review of 17 patients (2002-2013) showed a 10-year progression-free survival (PFS) rate of 67.4%, with the ETCA group showing fewer progressions and cranial neuropathies than those treated with combined approaches. The ETCA, a minimally invasive technique, provided a similar extent of resection compared to conventional skull-base approaches and enabled safe delivery of high-dose adjuvant radiotherapy. The findings suggest that ETCA is an effective treatment for centrally located clival chordomas.

Long Term Outcome and Quality of Life of Intracranial Meningioma Patients Treated with Pencil Beam Scanning Proton Therapy

The aim of this study was to assess the clinical outcome, including QoL, of patients with intracranial meningiomas WHO grade 1-3 who were treated with Pencil Beam Scanning Proton Therapy (PBS PT) between 1997 and 2022. Two hundred patients (median age 50.4 years, 70% WHO grade 1) were analyzed. Acute and late side effects were classified according to CTCAE version 5.0. Time to event data were calculated. QoL was assessed descriptively by the EORTC-QLQ-C30 and BN20 questionnaires. With a median follow-up of 65 months (range: 3.8-260.8 months) the 5 year OS was 95.7% and 81.8% for WHO grade 1 and grade 2/3, respectively (p < 0.001). Twenty (10%) local failures were observed. Failures occurred significantly (p < 0.001) more frequent in WHO grade 2 or 3 meningioma (WHO grade 1: n = 7, WHO grade 2/3: n = 13), in patients with multiple meningiomas (p = 0.005), in male patients (p = 0.005), and when PT was initiated not as upfront therapy (p = 0.011). There were no high-grade toxicities in the majority (n = 176; 88%) of patients. QoL was assessed for 83 (41.5%) patients and for those patients PT did not impacted QoL negatively during the follow-up. In summary, we observed very few local recurrences of meningiomas after PBS PT, a stable QoL, and a low rate of high-grade toxicity.

Clinical outcomes of benign brain tumors treated with single fraction LINAC-based stereotactic radiosurgery: Experience of a single institute

Objectives

Accelerator-based stereotactic radiosurgery (SRS) is a noninvasive and effective treatment modality widely used for benign brain tumors. This study aims to report 20-year treatment outcomes in our institute.

Materials and Methods

From May 2001 to December 2020, 127 patients treated with LINAC-based single-fraction SRS for their benign brain lesions were included. A neurosurgeon and two radiation oncologists retrospectively reviewed all data. Computed tomography (CT) simulation was performed after head-frame fixation under local anesthesia. All planning CT images were co-registered and fused with gadolinium-enhanced magnetic resonance imaging taken within 3 months for lesions targeting and critical organs delineation. The marginal dose was prescribed at 60%-90% isodose lines, respectively, to cover ≥95% planning target volume. Outcome evaluations included clinical tumor control rate (TCR), defined as the need for salvage therapy, and radiological response, defined as no enlargement of >2 cm in the maximal diameter. Overall survival (OS) and adverse reaction (defined according to CTCAE 5.0) were also analyzed.

Results

The present study included 76 female and 51 male patients for analysis. The median age was 59 years (range, 20-88 years). Their diagnoses were vestibular schwannoma (VS, n = 54), nonvestibular cranial nerve schwannoma (n = 6), meningioma (n = 50), and pituitary adenoma (n = 17). Totally 136 lesions were treated in a single fraction, predominantly skull base tumors, accounting for 69.1%. Median and mean follow-up duration was 49 and 61 months (range, 1-214 months), Overall TCR was 92.9%. The 5-year disease-specific TCR for VS, nonvestibular schwannoma, meningioma, and pituitary adenoma were 97.4%, 91.7%, 93.8%, and 83.3%. Salvage therapy was indicated for eight patients at 4-110 months after SRS. Among symptomatic patients, post-SRS symptom(s) was improved, stable, and worse in 68.2%, 24.3%, and 3.6%, respectively. Radiological response rate for 111 evaluable patients was 94.6% (shrinkage, 28.8%; stable, 65.8%). OS was 96.1% without treatment-related mortality. One patient with post-SRS cranial nerve injury (0.8%, involving the trigeminal nerve, grade 2 toxicities). No grade 3-4 acute or late toxicity was found.

Conclusion

Our results suggested that LINAC-based SRS effectively controls tumor growth and tumor-related neurological symptoms for patients with benign brain tumors. SRS is less aggressive, associated with low neurological morbidity and no mortality. Continuous follow-up is indicated to conclude longer outcomes.

Redefine the Role of Spot-Scanning Proton Beam Therapy for the Single Brain Metastasis Stereotactic Radiosurgery

Purpose

To explore the role of using Pencil Beam Scanning (PBS) proton beam therapy in single lesion brain stereotactic radiosurgery (SRS), we developed and validated a dosimetric in silico model to assist in the selection of an optimal treatment approach among the conventional Volumetric Modulated Arc Therapy (VMAT), Intensity Modulated Proton Therapy (IMPT) and Spot-scanning Proton Arc (SPArc).

Material and Methods

A patient’s head CT data set was used as an in silico model. A series of targets (volume range from 0.3 cc to 33.03 cc) were inserted in the deep central and peripheral region, simulating targets with different sizes and locations. Three planning groups: IMPT, VMAT, and SPArc were created for dosimetric comparison purposes and a decision tree was built based on this in silico model. Nine patients with single brain metastases were retrospectively selected for validation. Multiple dosimetric metrics were analyzed to assess the plan quality, such as dose Conformity Index (CI) (ratio of the target volume to 100% prescription isodose volume); R50 (ratio of 50% prescription isodose volume to the target volume); V_12Gy (volume of brain tissue minus GTV receiving 12 Gy), and mean dose of the normal brain. Normal tissue complication probability (NTCP) of brain radionecrosis (RN) was calculated using the Lyman-Kutcher-Burman (LKB) model and total treatment delivery time was calculated. Six physicians from different institutions participated in the blind survey to evaluate the plan quality and rank their choices.

Results

The study showed that SPArc has a dosimetric advantage in the V_12Gy and R50 with target volumes > 9.00 cc compared to VMAT and IMPT. A significant clinical benefit can be found in deep centrally located lesions larger than 20.00 cc using SPArc because of the superior dose conformity and mean dose reduction in healthy brain tissue. Nine retrospective clinical cases and the blind survey showed good agreement with the in silico dosimetric model and decision tree. Additionally, SPArc significantly reduced the treatment delivery time compared to VMAT (SPArc 184.46 ± 59.51s vs. VMAT: 1574.78 ± 213.65s).

Conclusion

The study demonstrated the feasibility of using Proton beam therapy for single brain metastasis patients utilizing the SPArc technique. At the current stage of technological development, VMAT remains the current standard modality of choice for single lesion brain SRS. The in silico dosimetric model and decision tree presented here could be used as a practical clinical decision tool to assist the selection of the optimal treatment modality among VMAT, IMPT, and SPArc in centers that have both photon and proton capabilities.

Dosimetric parameters associated with the long-term oncological outcomes of Gamma Knife surgery for sellar and parasellar tumors in pediatric patients

OBJECTIVE

The authors aimed to investigate the dosimetric parameter and the minimally required dose associated with long-term control of sellar and parasellar tumors after Gamma Knife surgery (GKS) in children.

METHODS

A retrospective analysis was performed on pediatric patients younger than 19 years of age who were diagnosed with sellar and parasellar tumors and received GKS at the authors' institution from 1998 to 2019. Cox proportional hazards regression analyses were used to investigate the dosimetric parameters associated with treatment outcome. The Kaplan-Meier method was used to analyze tumor control rates after GKS.

RESULTS

Overall, 37 patients with 40 sellar and parasellar tumors, including 22 craniopharyngiomas and 12 pituitary adenomas, had a mean follow-up of 85.8 months. The gross target volume was 0.05 cm3 to 15.28 cm3, and the mean marginal dose was 15.8 Gy (range 9.6-30.0 Gy). Ten patients experienced treatment failure at a mean of 28.0 ± 26.7 months. The actuarial 5- and 10-year tumor control rates were 79.0% and 69.8%, respectively. D98% was an independent predictive factor of tumor control (HR 0.846 [95% CI 0.749-0.956], p = 0.007), with a cutoff value of 11.5 Gy for the entire cohort and 10 Gy for the craniopharyngioma group. Visual deterioration occurred in 2 patients with the maximum point dose of 10.1 Gy and 10.6 Gy to the optic apparatus.

CONCLUSIONS

In pediatric patients, D98% was a reliable index of the minimum required dose for long-term control of sellar and parasellar tumors after GKS. The optimal D98% value for each tumor diagnosis needs to be elucidated in the future.

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.

Pituitary adenoma treatment plan quality comparison between linear accelerator volumetric modulated arc therapy and Leksell Gamma Knife® radiosurgery

The aim of this study was to compare radiosurgical treatment plan quality of a linear accelerator with Leksell Gamma Knife (LGK) for pituitary adenoma irradiation. Thirty pituitary adenoma patients were evaluated in this study. Treatment plans were prepared on LGK and stereotactic linear accelerator Varian TrueBeam STx. Volumetric Modulated Arc Therapy (VMAT) plans (21 plans with 2 coplanar arcs and 9 plans with 4 non-coplanar arcs) were calculated for linear accelerator. All the plans were evaluated in terms of conformity, selectivity, gradient index and organ at risk (OAR) sparing. VMAT produced dosimetrically comparable treatment plans to LGK regarding conformity and selectivity (New Conformity Index (NCI): 1.76 ± 0.65 for 4 arc VMAT, 2.33 ± 1,16 for 2 arc VMAT and 1.96 ± 0.71 for LGK; Selectivity Index (SI): 0.63 ± 0.16 for 4 arc VMAT, 0.51 ± 0.16 for 2 arc VMAT and 0.58 ± 0.17 for LGK). Gradient index (GI) was superior for LGK plans (GI: 2.74 ± 0.20 for LGK and 5.28 ± 2.29 for 4 arc VMAT). OAR sparing for optics, brainstem, and hypophysis was similar for both modalities while target volume coverage was maintained the same. Finally, treatment time resulted in favor of VMAT plans (in this study VMAT plans were almost 5 times faster than LGK treatment regarding beam on time). According to the results of this study stereotactic linear accelerator with VMAT treatment could be used as a reasonable alternative to LGK for pituitary adenoma radiosurgery but only if the same head fixation method accuracy and target volume delineation are maintained for both modalities.

Protons versus photons for the treatment of chordoma

BACKGROUND

Chordoma is a rare primary bone tumour with a high propensity for local recurrence. Surgical resection is the mainstay of treatment, but complete resection is often morbid due to tumour location. Similarly, the dose of radiotherapy (RT) that surrounding healthy organs can tolerate is frequently below that required to provide effective tumour control. Therefore, clinicians have investigated different radiation delivery techniques, often in combination with surgery, aimed to improve the therapeutic ratio.

OBJECTIVES

To assess the effects and toxicity of proton and photon adjuvant radiotherapy (RT) in people with biopsy-confirmed chordoma.

SEARCH METHODS

We searched CENTRAL (2021, Issue 4); MEDLINE Ovid (1946 to April 2021); Embase Ovid (1980 to April 2021) and online registers of clinical trials, and abstracts of scientific meetings up until April 2021.

SELECTION CRITERIA

We included adults with pathologically confirmed primary chordoma, who were irradiated with curative intent, with protons or photons in the form of fractionated RT, SRS (stereotactic radiosurgery), SBRT (stereotactic body radiotherapy), or IMRT (intensity modulated radiation therapy). We limited analysis to studies that included outcomes of participants treated with both protons and photons.

DATA COLLECTION AND ANALYSIS

The primary outcomes were local control, mortality, recurrence, and treatment-related toxicity. We followed current standard Cochrane methodological procedures for data extraction, management, and analysis. We used the ROBINS-I tool to assess risk of bias, and GRADE to assess the certainty of the evidence.

MAIN RESULTS

We included six observational studies with 187 adult participants. We judged all studies to be at high risk of bias. Four studies were included in meta-analysis. We are uncertain if proton compared to photon therapy worsens or has no effect on local control (hazard ratio (HR) 5.34, 95% confidence interval (CI) 0.66 to 43.43; 2 observational studies, 39 participants; very low-certainty evidence). Median survival time ranged between 45.5 months and 66 months. We are uncertain if proton compared to photon therapy reduces or has no effect on mortality (HR 0.44, 95% CI 0.13 to 1.57; 4 observational studies, 65 participants; very low-certainty evidence). Median recurrence-free survival ranged between 3 and 10 years. We are uncertain whether proton compared to photon therapy reduces or has no effect on recurrence (HR 0.34, 95% CI 0.10 to 1.17; 4 observational studies, 94 participants; very low-certainty evidence). One study assessed treatment-related toxicity and reported that four participants on proton therapy developed radiation-induced necrosis in the temporal bone, radiation-induced damage to the brainstem, and chronic mastoiditis; one participant on photon therapy developed hearing loss, worsening of the seventh cranial nerve paresis, and ulcerative keratitis (risk ratio (RR) 1.28, 95% CI 0.17 to 9.86; 1 observational study, 33 participants; very low-certainty evidence). There is no evidence that protons led to reduced toxicity. There is very low-certainty evidence to show an advantage for proton therapy in comparison to photon therapy with respect to local control, mortality, recurrence, and treatment related toxicity.

AUTHORS' CONCLUSIONS

There is a lack of published evidence to confirm a clinical difference in effect with either proton or photon therapy for the treatment of chordoma. As radiation techniques evolve, multi-institutional data should be collected prospectively and published, to help identify persons that would most benefit from the available radiation treatment techniques.

Design and characterization of a prototype tertiary device for proton beam stereotactic radiosurgery

Though potentially beneficial, proton beam stereotactic radiosurgery has not been adopted widely secondary to the technical challenge of safely delivering multiple focused beams of proton radiation. In this study, we describe the design and characterization of a proton beam stereotactic radiosurgery system that can be adopted by existing passive scattering systems. This system utilizes a helmet-like device in which patient-specific brass apertures required for final beam collimation are positioned on a scaffold that is separate from the treatment gantry. The proton snout is then fitted with a generic aperture to focus the primary proton beam onto the patient specific apertures that are in the helmet-like device. The patient-specific apertures can all be placed at the start of the treatment, thus treatment with multiple beams can be accomplished without the delay of switching the apertures. In this report we describe a prototype design of this collimation system and dosimetric testing to verify efficacy. Subsequently, we describe a custom 3D printing of a prototype device and report on overall localization accuracy using Winston-Lutz tests. Our results show that it is possible to develop an add-on device for proton beam radiosurgery that is safe and efficient and capable of wide adoption on existing proton delivery systems.

Advances in Multidisciplinary Management of Skull Base Meningiomas

The surgical management of Skull Base Meningiomas (SBMs) has radically changed over the last two decades. Extensive surgery for patients with SBMs represents the mainstream treatment; however, it is often challenging due to narrow surgical corridors and proximity to critical neurovascular structures. Novel surgical technologies, including three-dimensional (3D) preoperative imaging, neuromonitoring, and surgical instruments, have gradually facilitated the surgical resectability of SBMs, reducing postoperative morbidity. Total removal is not always feasible considering a risky tumor location and invasion of surrounding structures and brain parenchyma. In recent years, the use of primary or adjuvant stereotactic radiosurgery (SRS) has progressively increased due to its safety and efficacy in the control of grade I and II meningiomas, especially for small to moderate size lesions. Patients with WHO grade SBMs receiving subtotal surgery can be monitored over time with surveillance imaging. Postoperative management remains highly controversial for grade II meningiomas, and depends on the presence of residual disease, with optional upfront adjuvant radiation therapy or close surveillance imaging in cases with total resection. Adjuvant radiation is strongly recommended in patients with grade III tumors. Although the currently available chemotherapy or targeted therapies available have a low efficacy, the molecular profiling of SBMs has shown genetic alterations that could be potentially targeted with novel tailored treatments. This multidisciplinary review provides an update on the advances in surgical technology, postoperative management and molecular profile of SBMs.

Gamma Knife Stereotactic Radiosurgery for the treatment of chordomas and chondrosarcomas

INTRODUCTION

Primary chordomas and chondrosarcomas of the skull base are difficult tumours to treat successfully. Despite advances in surgical techniques, a gross total resection is often impossible to achieve. In addition, some patients may be deemed unsuitable or not wish to undergo extensive surgery for these conditions. This study examines the role of Gamma Knife Stereotactic Radiosurgery (GKRS) in the treatment of these difficult cases.

METHODS

All patients harbouring either a chordoma or chondrosarcoma treated at the National Centre for Stereotactic Radiosurgery, Royal Hallamshire Hospital, Sheffield, UK, between 1985 and 2018, were reviewed with regard to their clinical presentations, pre- and post-treatment imaging, GKRS prescriptions and outcomes.

RESULTS

In total, 24 patients with a mean tumour volume of 13 cm³ in the chordoma group (n=15) and 12 cm³ in the chondrosarcoma group (n=9) underwent GKRS. The 5- and 10-year overall survival rates for the chordoma group were 67% and 53% respectively, while for the chondrosarcoma group, they were 78% at both time points. The tumour control rates at 5 and 10 years in the chordoma group were 67% and 49% and for the chondrosarcoma group 78% at both time points. Patients with tumour volumes of less than 7 cm³ before GKRS treatment demonstrated a statistically significant longer overall survival rate (p=0.03).

CONCLUSIONS

GKRS offers a comparable option to proton beam therapy for the treatment of these tumours. Early intervention for tumour volumes of less than 7 cm³ gives the best long-term survival rates.

ESTRO ACROP guideline for target volume delineation of skull base tumors

BACKGROUND AND PURPOSE

For skull base tumors, target definition is the key to safe high-dose treatments because surrounding normal tissues are very sensitive to radiation. In the present work we established a joint ESTRO ACROP guideline for the target volume definition of skull base tumors.

MATERIAL AND METHODS

A comprehensive literature search was conducted in PubMed using various combinations of the following medical subjects headings (MeSH) and free-text words: "radiation therapy" or "stereotactic radiosurgery" or "proton therapy" or "particle beam therapy" and "skull base neoplasms" "pituitary neoplasms", "meningioma", "craniopharyngioma", "chordoma", "chondrosarcoma", "acoustic neuroma/vestibular schwannoma", "organs at risk", "gross tumor volume", "clinical tumor volume", "planning tumor volume", "target volume", "target delineation", "dose constraints". The ACROP committee identified sixteen European experts in close interaction with the ESTRO clinical committee who analyzed and discussed the body of evidence concerning target delineation.

RESULTS

All experts agree that magnetic resonance (MR) images with high three-dimensional spatial accuracy and tissue-contrast definition, both T2-weighted and volumetric T1-weighted sequences, are required to improve target delineation. In detail, several key issues were identified and discussed: i) radiation techniques and immobilization, ii) imaging techniques and target delineation, and iii) technical aspects of radiation treatments including planning techniques and dose-fractionation schedules. Specific target delineation issues with regard to different skull base tumors, including pituitary adenomas, meningiomas, craniopharyngiomas, acoustic neuromas, chordomas and chondrosarcomas are presented.

CONCLUSIONS

This ESTRO ACROP guideline achieved detailed recommendations on target volume definition for skull base tumors, as well as comprehensive advice about imaging modalities and radiation techniques.

Role of Proton Beam Therapy in Current Day Radiation Oncology Practice

Proton beam therapy (PBT), because of its unique physics of no–exit dose deposition in the tissue, is an exciting prospect. The phenomenon of Bragg peak allows protons to deposit their almost entire energy towards the end of the path of the proton and stops any further dose delivery. Braggs peak equips PBT with superior dosimetric advantage over photons or electrons because PBT doesn’t traverse the target/body but is stopped sharply at an energy dependent depth in the target/body. It also has no exit dose. Because of no exit dose and normal tissue sparing, PBT is hailed for its potential to bring superior outcomes. Pediatric malignancies is the most common malignancy where PBT have found utmost application. Nowadays, PBT is also being used in the treatment of other malignancies such as carcinoma prostate, carcinoma breast, head and neck malignancies, and gastrointestinal (GI) malignancies. Despite advantages of PBT, there is not only a high cost of setting up of PBT centers but also a lack of definitive phase-III data. Therefore, we review the role of PBT in current day practice of oncology to bring out the nuances that must guide the practice to choose suitable patients for PBT.

Current perspectives on recurrent pituitary adenoma: The role and timing of surgery vs adjuvant treatment

The clinical course of pituitary adenoma can be highly variable. Aggressive pituitary tumours may require multimodal therapy with multiple operations. Even standard pituitary adenomas exhibit relatively high long-term recurrence rates and delayed intervention is often required. The indications for revision surgery in the endoscopic era are expanding for both functioning and nonfunctioning tumours, including access to the cavernous sinus and intracranial compartments. Although revision surgery can be challenging, it has been demonstrated to be both safe and effective. The question of the use of early radiotherapy in pituitary adenoma remains controversial. Our increasing understanding of pituitary tumour biology facilitates individualized treatment and surveillance protocols, with early intervention in high-risk adenoma subtypes. In this review, we discuss the treatment options for recurring pituitary tumours and focus on the role of revision surgery.

Radiotherapy of Parasellar Tumours

Parasellar tumours represent a wide group of intracranial lesions, both benign and malignant. They may arise from several structures located within the parasellar area or they may infiltrate or metastasize this region. The treatment of the tumours located in these areas is challenging because of their complex anatomical location and their heterogenous histology. It often requires a multimodal approach, including surgery, radiation therapy (RT), and medical therapy. Due to the proximity of critical structures and the risks of side effects related to the procedure, a successful surgical resection is often not achievable. Thus, RT plays a crucial role in the treatment of several parasellar tumours. Conventional fractionated RT and modern radiation techniques, like stereotactic radiosurgery and proton beam RT, have become a standard management option, in particular for cases with residual or recurrent tumours after surgery and for those cases where surgery is contraindicated. This review examines the role of RT in parasellar tumours analysing several techniques, outcomes and side effects.

Lower doses to hippocampi and other brain structures for skull-base meningiomas with intensity modulated proton therapy compared to photon therapy

BACKGROUND AND PURPOSE

Radiotherapy of skull-base meningiomas is challenging due to the close proximity of multiple sensitive organs at risk (OARs). This study systematically compared intensity modulated proton therapy (IMPT), non-coplanar volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) based on automated treatment planning. Differences in OARs sparing, with specific focus on the hippocampi, and low-dose delivery were quantified.

MATERIALS AND METHODS

Twenty patients, target diameter >3 cm, were included. Automated plan generation was used to calculate a VMAT plan with three non-coplanar arcs, an IMRT plan with nine non-coplanar beams with optimized gantry and couch angles, and an IMPT plan with three patient-specific selected non-coplanar beams. A prescription dose of 50.4 GyRBE in 28 fractions was used. The same set of constraints and prioritized objectives was used. All plans were rescaled to the same target coverage. Repeated measures ANOVA was used to assess the statistical significance of differences in OAR dose parameters between planning techniques.

RESULTS

Compared to VMAT and IMRT, IMPT significantly improved dose conformity to the target volume. Consequently, large dose reductions in OARs were observed. With respect to VMAT, the mean dose and D_40% in the bilateral hippocampus were on average reduced by 48% and 74%, respectively (p ≤ 0.005). With IMPT, the mean dose in the normal brain and volumes receiving 20-30 Gy were up to 47% lower (p ≤ 0.01). When comparing IMPT and IMRT, even larger dose differences in those OARs were observed.

CONCLUSION

For skull-base meningiomas IMPT allows for a considerable dose reduction in the hippocampi, normal brain and other OARs compared to both non-coplanar VMAT and IMRT, which may lead to a clinically relevant reduction of late neurocognitive side effects.

Linear Accelerator-Based Radiosurgery of Grade I Intracranial Meningiomas

Objective

To determine the local control rate and complication rate in the treatment of grade I intracranial meningiomas.

Methods

A retrospective study was performed of patients with grade I meningioma who received radiosurgery with a dedicated linear accelerator from January 2002 to August 2012 with a minimum follow-up of 2 years. We performed descriptive statistics, logistic regression, and progression-free survival analysis through a Kaplan-Meier curve.

Results

Seventy-five patients with 78 grade I meningiomas received radiosurgery, 39 underwent surgery plus adjuvant radiosurgery, and 36 only radiosurgery. The follow-up median time was 68 months (range, 35–120 months). The tumor control rate was 93%, the 5-year progression-free survival was 92% (95% confidence interval, 77%–98%). Acute toxicity was 2.6%, and grade 1–2 late toxicity was 26.6%. Postradiosurgery edema was the main late morbidity. Age >55 years was the only significant factor for attaining a response >75%. The background of surgery before radiosurgery was the only significant prognostic factor for showing edema (odds ratio 5.78 [95% confidence interval, 2.14–15.64]).

Conclusions

The local control rate attained in our series is similar to that reported in other series worldwide; the acute toxicity rate was low and late toxicity was moderate.

Skull base chordoma treated with proton therapy: A systematic review

Background:

Chordoma located in the skull base is usually a challenging surgical condition. It is often not possible to achieve gross total resection. Residual tumors have been treated with adjuvant focal radiation therapy employing high-energy particles most commonly through proton beam. In this review, we systematically analyzed indications and outcomes of this treatment with respect to local control rates of the lesion and factors determining recurrence of skull base chordomas. In addition, we collected data on treatment-associated radiation-induced side effects.

Methods:

In line with the PRISMA guidelines, the authors performed a literature search algorithm for relevant articles using three databases: PubMed, Embase, and Cochrane. Inclusion and exclusion criteria were applied to evaluate all identified studies published between 1980 and 2018.

Results:

Our review included 11 studies for analysis (n = 511 patients). The mean age of the study population was 47.3 ± 5.8 years. The mean dose of postsurgical irradiation at the time of initial treatment was 71.1 ± 3.1 Gy. The mean follow-up duration was 45.0 ± 17.5 months. Within this follow-up duration, recurrence occurred in 26.8% of the patients. The mean time to recurrence was 34.5 ± 15.2 months. A significant number of patients experienced side effects varying from Grade 1 (mild dermatitis) to Grade 4 (temporal lobe necrosis and visual disorders).

Conclusion:

Despite advances in proton therapy, recurrence rates in skull base chordoma remain high. The toxicity of proton therapy may be more prevalent than generally thought. Unfortunately, there is substantial variation in the methods of data reporting.

Effect of Irradiation Time on Biological Effectiveness and Tumor Control Probability in Proton Therapy

PURPOSE

The biological effectiveness of proton beams may decrease with irradiation time because of sublethal damage repair (SLDR). The purpose of this study is to systematically evaluate this effect in hypofractionated proton therapy for various target sizes, depths, and prescribed doses per fraction.

METHODS AND MATERIALS

Plans with a single spread-out Bragg peak beam were created using a constant relative biological effectiveness (RBE) of 1.1 to cover targets of 6 different sizes located at 3 different depths in water. Biological doses of 2, 3, 5, 10, and 20 Gy (RBE) were prescribed to the targets. First, to investigate the depth variation of the biological effectiveness, the biological dose in instantaneous irradiation was recalculated based on the microdosimetric kinetic model. SLDR was then taken into account in the microdosimetric kinetic model during treatments to obtain the irradiation time-dependent biological effectiveness for irradiation time T of 5 to 60 minutes and beam interruption time τ of 0 to 60 minutes. The tumor control probabilities were calculated for single-fraction proton therapy fields of different Ts and τs, and the curative doses were evaluated at a tumor control probability of 90%.

RESULTS

The biological effectiveness decreased with longer T and τ and higher prescribed dose. The maximum decrease in the biological effectiveness was 21% with a 20 Gy (RBE) prescribed dose. In single-fraction proton therapy, the curative dose increased linearly by approximately 33% to 35% with the increase of T from 0 to 60 minutes.

CONCLUSIONS

The biological effectiveness varies largely with T and τ because of SLDR during treatments. This effect was pronounced for high prescribed doses per fraction. Thus, the effect of SLDR needs to be considered in hypofractionated and single-fraction proton therapies in relation to size and depth of the target.

Surgery and protontherapy in Grade I and II skull base chondrosarcoma: A comparative retrospective study

Objective

Skull base chondrosarcoma is a rare tumour usually treated by surgery and proton therapy. However, as mortality rate is very low and treatment complications are frequent, a less aggressive therapeutic strategy could be considered. The objective of this study was to compare the results of surgery only vs surgery and adjuvant proton therapy, in terms of survival and treatment adverse effects, based on a retrospective series.

Methods

Monocentric retrospective study at a tertiary care centre. All patients treated for a skull base grade I and II chondrosarcoma were included. We collected data concerning surgical and proton therapy treatment and up-to-date follow-up, including Common Terminology Criteria for Adverse Events (CTCAE) scores.

Results

47 patients (23M/24F) were operated on between 2002 and 2015; mean age at diagnosis was 47 years-old (10–85). Petroclival and anterior skull base locations were found in 34 and 13 patients, respectively. Gross total resection was achieved in 17 cases (36%) and partial in 30 (64%). Adjuvant proton therapy (mean total dose 70 GyRBE,1.8 GyRBE/day) was administered in 23 cases. Overall mean follow-up was 91 months (7–182). Of the patients treated by surgery only, 8 (34%) experienced residual tumour progression (mean delay 51 months) and 5 received second-line proton therapy. Adjuvant proton therapy was associated with a significantly lower rate of relapse (11%; p = 0.01). There was no significant difference in 10-year disease specific survival between patients initially treated with or without adjuvant proton therapy (100% vs 89.8%, p = 0.14). Difference in high-grade toxicity was not statistically significant between patients in both groups (25% (7) vs 11% (5), p = 0.10). The most frequent adverse effect of proton therapy was sensorineural hearing loss (39%).

Conclusion

Long-term disease specific survival was not significantly lower in patients without adjuvant proton therapy, but they experienced less adverse effects. We believe a surgery only strategy could be discussed, delaying as much as possible proton therapy in cases of relapse. Further prospective studies are needed to validate this more conservative strategy in skull base chondrosarcoma.

Fractionated Proton Beam Therapy for Acoustic Neuromas: Tumor Control and Hearing Preservation

Purpose

This prospective cohort evaluated patients with acoustic neuroma treated with proton irradiation at Loma Linda University Medical Center. A dose of 50.4 Gy in 28 fractions was given to improve hearing preservation while maintaining tumor control.

Patients and Methods

Ninety-five patients were treated from March 1991 to March 2008. Fractionated proton radiotherapy at daily doses of 1.8 Gy was employed. Patients were treated to 1 of 3 total doses: 59.4 Gy, used initially for patients without serviceable hearing; 54 Gy, used for patients with serviceable hearing through October 2000; and 50.4 Gy used since 2001 for patients with serviceable hearing. Survival and local control were calculated using the Kaplan-Meier method. Logistic regression analysis was preformed comparing dose, tumor size, and tumor location with hearing preservation.

Results

Ninety-four patients were assessable; the median follow-up was 64 months. Five-year local control rates for the 59.4 Gy, 54 Gy, and 50.4 Gy groups were 95%, 97%, and 92%, respectively (P = .80); the overall 10-year actuarial control rate was 90%. Cranial nerve injuries occurred in <5% in all groups. Four-year actuarial rates of hearing preservation were maintained in 44% of patients treated with 54 Gy and 64% treated with 50.4 Gy (P = .284). On multivariate analysis, initial tumor diameter (≤1.5 cm) was found to be a prognostic factor for maintaining serviceable hearing in both groups (P = .011).

Conclusions

Fractionated proton therapy of 50.4 Gy offers excellent local control and minimal cranial nerve toxicities. Improved rates of hearing preservation that are comparable with radiosurgery were seen with 50.4 Gy compared with higher doses, although this did not reach significance. Maintaining hearing was found to be associated with smaller initial tumor size.

Radiologic Response and Disease Control of Recurrent Intracranial Meningiomas Treated With Reirradiation

PURPOSE

To evaluate the clinical outcomes of reirradiation of recurrent meningiomas and factors related to patient selection and treatment modality.

METHODS AND MATERIALS

Recurrent meningioma patients who failed prior stereotactic radiosurgery (SRS) or fractionated external beam radiation therapy (EBRT) received reirradiation using either SRS or EBRT. Complete response (CR), partial response (PR), and progression after reirradiation were evaluated using the MacDonald criteria. Local control (LC), progression-free survival (PFS), and overall survival (OS) after reirradiation were analyzed using the Kaplan-Meier method. Logistic and Cox regression analyses were performed to identify factors associated with reirradiation modality and PFS, respectively.

RESULTS

Forty-three patients (14 grade 1/unknown, 29 grade 2/3) were reirradiated with SRS (67%) or EBRT (33%). Median time from initial SRS/EBRT to reirradiation was 60 months (range, 7.5-202); median tumor volume at the time of reirradiation was 4.8 cm³ (range, 0.14-64). After a median radiologic follow-up of 19.4 months, the response rate (CR + PR) was 8% for grade 1 and 20% for grade 2/3 meningiomas. After 2 years, LC was 78%, PFS was 63%, and OS was 80%. Larger tumor volume and prior SRS were associated with reirradiation using EBRT. Reirradiated grade 2/3 meningiomas had significantly worse PFS than grade 1 (2-year PFS: 50% vs 92%, respectively; P = .02) but not LC (P = .11) or OS (P = .39). On multivariable analysis, worse PFS was significantly associated with grade 2/3 histology (hazard ratio, 3.92; 95% confidence interval, 1.33-11.6) as well as worse Karnofsky Performance Scale score but not reirradiation dose, volume, and modality. Grades 3 to 4 radiation necrosis developed in 4 patients (10%).

CONCLUSIONS

Reirradiation of recurrent meningiomas appears to be feasible with promising clinical outcomes and an acceptable toxicity profile.

Gamma Knife and volumetric modulated arc therapy stereotactic radiosurgery plan quality and OAR sparing comparison for pituitary adenomas and vestibular schwannomas

PURPOSE

To compare the plan quality and organs at risk (OAR) sparing of auto-planned volumetric modulated art therapy (VMAT) and Gamma Knife (GK) for stereotactic radiosurgery of pituitary adenomas (PA) and vestibular schwannomas (VS).

METHODS

VMAT radiosurgery plans were made using auto planning tool for eight vestibular schwannoma and eight pituitary adenoma patients previously treated with GK. VMAT plans were made with three non-coplanar arcs using 315, 0 and 45 degrees angles, 6MV FFF energy at 1400 MU/min dose rate and 2.5 mm thick MLC leaves. Both GK and VMAT plans were prescribed to similar isodose lines (50% - 60%).

RESULTS

Respectively for GK and VMAT, the mean Paddick conformity index (PCI) was 0.62 ± 0.08 and 0.67 ± 0.10 (p > 0.05) for PA and 0.72 ± 0.09 and 0.660 ± 0.13 (p > 0.05) for VS; the mean gradient index (GI) was 2.76 ± 0.14 and 3.14 ± 0.40 Gy (p < 0.05) for PA and 3.71 ± 1.83 and 3.60 ± 0.84 Gy (p > 0.05) for VS; mean brainstem maximum dose was 9.13 ± 3.50 Gy and 7.31 ± 2.01 Gy (p > 0.05) for PA and 11.67 ± 4.56 Gy and 12.22 ± 4.55 Gy (p > 0.05) for VS; mean optic nerve maximum dose was 9.66 ± 1.0 Gy and 7.67 ± 2.58 Gy (p < 0.05); mean cochlea mean dose was 7.31 ± 2.7 Gy and 7.23 ± 3.13 Gy (p > 0.05); and mean treatment time was 68 min and 5 min for PA and 40 min and 3 min for VS.

CONCLUSIONS

Auto planning with standard template simplified the planning stage for VMAT and provided clinically acceptable plans. Comparison of GK and VMAT for plan quality and OAR sparing varied across patients but both were overall comparable.

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.

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.

Skull base bony lesions: Management nuances; a retrospective analysis from a Tertiary Care Centre

Background:

Skull base lesions are not uncommon, but their management has been challenging for surgeons. There is large no of bony tumors at the skull base which has not been studied in detail as a group. These tumors are difficult not only because of their location but also due to their variability in the involvement of important local structure. Through this retrospective analysis from a Tertiary Care Centre, we are summarizing the details of skull base bony lesions and its management nuances.

Materials and Methods:

The histopathologically, radiologically, and surgically proven cases of skull base bony tumors or lesions involving bone were analyzed from the neurosurgery, neuropathology record of our Tertiary Care Institute from January 2009 to January 2014. All available preoperative and postoperative details were noted from their case files. The extent of excision was ascertained from operation records and postoperative magnetic resonance imaging if available.

Results:

We have surgically managed 41 cases of skull base bony tumors. It includes 11 patients of anterior skull base, 13 middle skull base, and 17 posterior skull base bony tumors. The most common bony tumor was chordoma 15 (36.6%), followed by fibrous dysplasia 5 (12.2%), chondrosarcoma (12.2%), and ewings sarcoma-peripheral primitive neuroectodermal tumor (EWS-pPNET) five cases (12.2%) each. There were more malignant lesions (n = 29, 70.7%) at skull base than benign (n = 12, 29.3%) lesions. The surgical approach employed depended on location of tumor and pathology. Total mortality was 8 (20%) of whom 5 patients were of histological proven EWS-pPNET.

Conclusions:

Bony skull base lesion consists of wide variety of lesions, and requires multispecialty management. The complex lesions required tailored approaches surgery of these lesions. With the advent of microsurgical and endoscopic techniques, and use of navigation better outcomes are being seen, but these lesions require further study for development of proper management plan.

Ischemic stroke after radiation therapy for pituitary adenomas: a systematic review

Radiation therapy is widely used for the treatment of residual and recurrent pituitary adenomas and proved to effectively control tumor growth. However, it is suggested that this treatment might result in an increased risk of ischemic stroke. This review aims to evaluate the radiotherapy-related risk of stroke in pituitary adenoma patients. PubMed and Embase databases were systematically searched for current literature on ischemic stroke risk after radiotherapy in pituitary adenoma, in accordance with the PRISMA statement. Two authors independently selected eligible studies and extracted data. The New Castle Ottawa-scale was used for quality assessment. Out of 264 publications, 11 studies were selected, including 4394 irradiated patients. Incidence of ischemic stroke ranged from 0 to 11.6% (mean 6.7%). While one large, long term follow-up study showed a threefold increased risk of stroke after radiation therapy, another nationwide study of high quality found no significant difference in stroke risk after irradiation. Four studies, which applied stereotactic radiosurgery (SRS) or Gamma-knife surgery (GKS), found no ischemic strokes. Included studies described different radiation techniques and regimens and different lengths of follow-up. In conclusion, complications of cerebral ischemia after radiotherapy for pituitary adenoma are infrequently reported. Moreover, after correction for several confounders, no significant difference in ischemic stroke rate between irradiated and non-irradiated patients could be identified.

Management of Chordoma and Chondrosarcoma with Fractionated Stereotactic Radiotherapy

OBJECTIVE

To evaluate the efficacy and toxicity of fractionated stereotactic radiotherapy (FSRT) for chordoma and chondrosarcoma.

METHODS

Twenty consecutive patients with a histopathologic diagnosis of chordoma (n = 16) or chondrosarcoma (n = 4) treated between 2010 and 2016 were retrospectively identified. All patients underwent FSRT in five fractions to a median dose of 37.5 Gy (range: 25-40 Gy) and followed with serial magnetic resonance imaging. Overall survival (OS), local recurrence-free survival (LRFS), and event-free survival (EFS) were estimated using the Kaplan-Meier method.

RESULTS

With a median follow-up of 28 months after FSRT and 40 months after initial surgery, crude OS and LRFS were 90%. Nine patients (45%) reported grade 1-3 acute toxicity, and two patients (10%) experienced grade 4, 5 late toxicity. One patient previously treated with proton therapy died from radiation vasculopathy 9 months after FSRT. The use of FSRT for recurrent disease or in patients with prior radiation therapy was associated with significantly decreased EFS.

CONCLUSION

FSRT for chordoma and chondrosarcoma is associated with high rates of OS and local control. Although many patients experience acute toxicity, there is a low incidence of late toxicity or irreversible treatment related morbidity despite the frequency of prior radiotherapy in this population. FSRT is an effective adjuvant or salvage treatment for chordoma and chondrosarcoma.

Low-Dose Gamma Knife Radiosurgery for Vestibular Schwannomas: Tumor Control and Cranial Nerve Function Preservation After 11 Gy

OBJECTIVES

This study aims to report tumor control rates and cranial nerve function after low dose (11.0 Gy) Gamma knife radiosurgery (GKRS) in patients with vestibular schwannomas.

METHODS

A retrospective chart review was performed on 30 consecutive patients with vestibular schwannomas treated from March 2004 to August 2010 with GKRS at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University. The marginal dose for all patients was 11.0 Gy prescribed to the 50% isodose line. Median follow-up time was 42 months. The median treatment volume was 0.53 cm3. Hearing data were obtained from audiometry reports before and after radiosurgery.

RESULTS

The actuarial progression free survival (PFS) based on freedom from surgery was 100% at 5 years. PFS based on freedom from persistent growth was 91% at 5 years. One patient experienced tumor progression requiring resection at 87 months. Serviceable hearing, defined as Gardner-Robertson score of I-II, was preserved in 50% of patients. On univariate and multivariate analyses, only higher mean and maximum dose to the cochlea significantly decreased the proportion of patients with serviceable hearing.

CONCLUSION

Vestibular schwannomas can be treated with low doses (11.0 Gy) of GKRS with good tumor control and cranial nerve preservation.

Target delineation and optimal radiosurgical dose for pituitary tumors

Stereotactic radiosurgery (SRS) delivered as either single-fraction or multi-fraction SRS (2–5 fractions) is frequently employed in patients with residual or recurrent pituitary adenoma. The most common delivery systems used for SRS include the cobalt-60 system Gamma Knife, the CyberKnife (CK) robotic radiosurgery system, or a modified conventional radiotherapy machine (linear accelerator, LINAC). Tumor control and normalization of hormone hypersecretion have been reported in 75–100 % and 25–80 % of patients, respectively. Hypopituitarism is the most commonly reported late complication of radiation treatment, whereas other toxicities occur less frequently. We have provided an overview of the recent available literature on SRS in patients with a pituitary adenoma. Critical aspects of pituitary irradiation, including target delineation and doses to organs at risk, optimal radiation dose, as well as the long-term efficacy and toxicity of SRS for either nonfunctioning or secreting pituitary adenomas are discussed. Single-fraction SRS represents an effective treatment for patients with a pituitary adenoma; however, caution should be used for lesions > 2.5–3 cm in size and/or involving the anterior optic pathway. Future studies will be necessary to optimize target doses and critical organ dose constrains in order to reduce the long-term toxicity of treatments while maintaining high efficacy.

Partial skull base tumour resection in combination with radiosurgery: an escape procedure or a reasonable solution of treatment?

Despite advancement in microsurgical techniques for skull base tumour surgery, approaches of this kind still represent a significant challenge for neurosurgeons due to the size of the tumour and its interference and proximity to important neural and vascular structures. After incomplete resection, gamma knife radiosurgery is becoming an alternative or adjunctive treatment option. In this article, some examples of our experience in combined treatment of the skull base tumours with surgical procedure and gamma knife therapy for the remaining tumour tissue are presented.

Remote acute demyelination after focal proton radiation therapy for optic nerve meningioma

We present a unique patient with delayed onset, acute demyelination that occurred distant to the effective field of radiation after proton beam radiotherapy for an optic nerve sheath meningioma. The use of stereotactic radiotherapy as an effective treatment modality for some brain tumors is increasing, given technological advances which allow for improved targeting precision. Proton beam radiotherapy improves the precision further by reducing unnecessary radiation to surrounding tissues. A 42-year-old woman was diagnosed with an optic nerve sheath meningioma after initially presenting with vision loss. After biopsy of the lesion to establish diagnosis, the patient underwent stereotactic proton beam radiotherapy to a small area localized to the tumor. Subsequently, the patient developed a large enhancing mass-like lesion with edema in a region outside of the effective radiation field in the ipsilateral frontal lobe. Given imaging features suggestive of possible primary malignant brain tumor, biopsy of this new lesion was performed and revealed an acute demyelinating process. This patient illustrates the importance of considering delayed onset acute demyelination in the differential diagnosis of enhancing lesions in patients previously treated with radiation.

Image-guided, intensity-modulated radiation therapy (IG-IMRT) for skull base chordoma and chondrosarcoma: preliminary outcomes

BACKGROUND

We report our preliminary outcomes following high-dose image-guided intensity modulated radiotherapy (IG-IMRT) for skull base chordoma and chondrosarcoma.

METHODS

Forty-two consecutive IG-IMRT patients, with either skull base chordoma (n = 24) or chondrosarcoma (n = 18) treated between August 2001 and December 2012 were reviewed. The median follow-up was 36 months (range, 3-90 mo) in the chordoma cohort, and 67 months (range, 15-125) in the chondrosarcoma cohort. Initial surgery included biopsy (7% of patients), subtotal resection (57% of patients), and gross total resection (36% of patients). The median IG-IMRT total doses in the chondrosarcoma and chordoma cohorts were 70 Gy and 76 Gy, respectively, delivered with 2 Gy/fraction.

RESULTS

For the chordoma and chondrosarcoma cohorts, the 5-year overall survival and local control rates were 85.6% and 65.3%, and 87.8% and 88.1%, respectively. In total, 10 patients progressed locally: 8 were chordoma patients and 2 chondrosarcoma patients. Both chondrosarcoma failures were in higher-grade tumors (grades 2 and 3). None of the 8 patients with grade 1 chondrosarcoma failed, with a median follow-up of 77 months (range, 34-125). There were 8 radiation-induced late effects-the most significant was a radiation-induced secondary malignancy occurring 6.7 years following IG-IMRT. Gross total resection and age were predictors of local control in the chordoma and chondrosarcoma patients, respectively.

CONCLUSIONS

We report favorable survival, local control and adverse event rates following high dose IG-IMRT. Further follow-up is needed to confirm long-term efficacy.

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.

Diagnostic Approach, Treatment, and Outcomes of Cervical Sympathetic Chain Schwannomas

Objective

This review examined the diagnostic approach, surgical treatment, and outcomes of cervical sympathetic chain schwannomas (CSCS) to guide clinical decision making.

Data Sources

Medline, EMBASE, and Cochrane databases.

Review Methods

A literature review from 1998 to 2013 identified 156 articles of which 51 representing 89 CSCS cases were evaluated in detail. Demographic, clinical, and outcomes data were extracted by 2 independent reviewers with high interrater reliability (κ = .79). Cases were mostly international (82%), predominantly from Asia (50%) and Europe (27%).

Conclusions

On average, patients were 42.6 years old (SD = 13.3) and had a neck mass ranging between 2 to 4 cm (52.7%) or >4 cm (43.2%). Nearly 70% of cases were asymptomatic at presentation. Presurgical diagnosis relied on CT (63.4%), MRI (59.8%), or both (19.5%), supplemented by cytology (33.7%), which was nearly always inconclusive (96.7%). US-treated cases were significantly more likely to receive presurgical MRI than internationally treated cases but less likely to have cytology ( P < .05). Presurgical diagnosis was challenging, with only 11% confirmatory accuracy postsurgically. Irrespective of mass size, extracapsular resection (ie, complete resection with nerve sacrifice) was the most frequently (87.6%) performed surgical procedure. Common postsurgical adverse events included Horner’s syndrome (91.1%), first bite syndrome (21.1%), or both (15.7%), with higher prevalence when mass size was >4 cm. Adverse events persisted in 82.3% of cases at an average 30.0 months (SD = 30.1) follow-up time.

Implications for Practice

Given the typical CSCS patient is young and asymptomatic and the likelihood of persistent morbidity is high with standard surgical approaches, less invasive treatment options warrant consideration.

Critical appraisal of RapidArc radiosurgery with flattening filter free photon beams for benign brain lesions in comparison to GammaKnife: a treatment planning study

BACKGROUND

To evaluate the role of RapidArc (RA) for stereotactic radiosurgery (SRS) of benign brain lesions in comparison to GammaKnife (GK) based technique.

METHODS

Twelve patients with vestibular schwannoma (VS, n = 6) or cavernous sinus meningioma (CSM, n = 6) were planned for both SRS using volumetric modulated arc therapy (VMAT) by RA. 104 MV flattening filter free photon beams with a maximum dose rate of 2400 MU/min were selected. Data were compared against plans optimised for GK. A single dose of 12.5 Gy was prescribed. The primary objective was to assess treatment plan quality. Secondary aim was to appraise treatment efficiency.

RESULTS

For VS, comparing best GK vs. RA plans, homogeneity was 51.7 ± 3.5 vs. 6.4 ± 1.5%; Paddick conformity Index (PCI) resulted 0.81 ± 0.03 vs. 0.84 ± 0.04. Gradient index (PGI) was 2.7 ± 0.2 vs. 3.8 ± 0.6. Mean target dose was 17.1 ± 0.9 vs. 12.9 ± 0.1 Gy. For the brain stem, D(1cm3) was 5.1 ± 2.0 Gy vs 4.8 ± 1.6 Gy. For the ipsilateral cochlea, D(0.1cm3) was 1.7 ± 1.0 Gy vs. 1.8 ± 0.5 Gy. For CSM, homogeneity was 52.3 ± 2.4 vs. 12.4 ± 0.6; PCI: 0.86 ± 0.05 vs. 0.88 ± 0.05; PGI: 2.6 ± 0.1 vs. 3.8 ± 0.5; D(1cm3) to brain stem was 5.4 ± 2.8 Gy vs. 5.2 ± 2.8 Gy; D(0.1cm3) to ipsi-lateral optic nerve was 4.2 ± 2.1 vs. 2.1 ± 1.5 Gy; D(0.1cm3) to optic chiasm was 5.9 ± 3.1 vs. 4.5 ± 2.1 Gy. Treatment time was 53.7 ± 5.8 (64.9 ± 24.3) minutes for GK and 4.8 ± 1.3 (5.0 ± 0.7) minutes for RA for schwannomas (meningiomas).

CONCLUSIONS

SRS with RA and FFF beams revealed to be adequate and comparable to GK in terms of target coverage, homogeneity, organs at risk sparing with some gain in terms of treatment efficiency.

Current concepts in clinical radiation oncology

Based on its potent capacity to induce tumor cell death and to abrogate clonogenic survival, radiotherapy is a key part of multimodal cancer treatment approaches. Numerous clinical trials have documented the clear correlation between improved local control and increased overall survival. However, despite all progress, the efficacy of radiation-based treatment approaches is still limited by different technological, biological, and clinical constraints. In principle, the following major issues can be distinguished: (1) The intrinsic radiation resistance of several tumors is higher than that of the surrounding normal tissue, (2) the true patho-anatomical borders of tumors or areas at risk are not perfectly identifiable, (3) the treatment volume cannot be adjusted properly during a given treatment series, and (4) the individual heterogeneity in terms of tumor and normal tissue responses toward irradiation is immense. At present, research efforts in radiation oncology follow three major tracks, in order to address these limitations: (1) implementation of molecularly targeted agents and 'omics'-based screening and stratification procedures, (2) improvement of treatment planning, imaging, and accuracy of dose application, and (3) clinical implementation of other types of radiation, including protons and heavy ions. Several of these strategies have already revealed promising improvements with regard to clinical outcome. Nevertheless, many open questions remain with individualization of treatment approaches being a key problem. In the present review, the current status of radiation-based cancer treatment with particular focus on novel aspects and developments that will influence the field of radiation oncology in the near future is summarized and discussed.