Sparing of the hippocampus, limbic circuit and neural stem cell compartment during partial brain radiotherapy for glioma: A dosimetric feasibility study

Actual, Personalized Approaches to Preserve Cognitive Functions in Brain Metastases Breast Cancer Patients

Simple Summary

Breast cancer is the one of most common causes of brain metastases among solid malignancies, being responsible for 10–16% of all brain metastases in oncological patients. Brain metastases in the course of breast cancer significantly worsen quality of life of patients, especially in the aspect of neurocognitive domains. The review aims to summarize and integrate the current knowledge about breast cancer brain metastases, focusing on indications of certain types of treatment, and with special attention to the role of hippocampus sparing in preserving neurocognitive functions in irradiated patients.

Abstract

Breast cancer (BC) is the most often diagnosed cancer among women worldwide and second most common cause of brain metastases (BMs) among solid malignancies being responsible for 10–16% of all BMs in oncological patients. Moreover, BMs are associated with worse prognosis than systemic metastases. The quality of life (QoL) among brain metastases breast cancer (BMBC) patients is significantly influenced by cognitive functions. Cancer-related cognitive deficits and the underlying neural deficits in BMBC patients can be caused via BMs per se, chemotherapy administration, brain irradiation, postmenopausal status, or comorbidities. Brain RT often leads to cognitive function impairment by damage of neural progenitor cells of the hippocampus and hence decreased QoL. Sparing the hippocampal region of the brain during RT provides protective covering of the centrally located hippocampi according to the patient’s clinical requirements. This article discusses the personalized strategies for treatment options to protect cognitive functions in BMBC patients, with special emphasis on the innovative techniques of radiation therapy.

Radiation guidelines for gliomas

Gliomas are the most frequent primary brain tumour. The proximity of organs at risk, the infiltrating nature, and the radioresistance of gliomas have to be taken into account in the choice of prescribed dose and technique of radiotherapy. The management of glioma patients is based on clinical factors (age, KPS) and tumour characteristics (histology, molecular biology, tumour location), and strongly depends on available and associated treatments, such as surgery, radiation therapy, and chemotherapy. The knowledge of molecular biomarkers is currently essential, they are increasingly evolving as additional factors that facilitate diagnostics and therapeutic decision-making. We present the update of the recommendations of the French society for radiation oncology on the indications and the technical procedures for performing radiation therapy in patients with gliomas.

Effects of brain radiotherapy on cognitive performance in adult low-grade glioma patients: A systematic review

Grade II gliomas are slow growing tumours that usually affect younger patients. The mainstream treatment modality at present is surgical. The role of radiation therapy in the management of grade II gliomas has been the subject of considerable debate. Radiation therapy has a proven potential to prolong progression free and overall survival in high-risk patients, but may also produce long-term cognitive deficits. Since grade II glioma patients are expected to live several years, retention of cognitive capacity and quality of life is an equally important endpoint as prolonging progression free survival. Our overarching goal is to critically review the available evidence on the possible neuropsychological effects of postoperative radiotherapy in adult grade II glioma patients. We performed a systematic literature search in Medline, Embase and Cochrane databases up to 1st of May 2020 for studies assessing the cognitive effects of radiation therapy on grade II glioma patients. Eleven studies meeting our inclusion criteria provide either negative or contradictory data regarding the cognitive domains affected, while major confounding variables remain incompletely addressed. The available evidence does not adequately support the notion that current radiation therapy protocols independently produce substantial cognitive decline in grade II glioma patients and therefore it would be premature to argue that radiation associated cognitive morbidity outweighs the benefit of prolonged survival. A large prospective study incorporating a full battery of neuropsychological testing, sufficiently long-term follow-up period and tight control of confounders is due to provide high quality data.

Recommendation for the contouring of limbic system in patients receiving radiation treatment: A pictorial review for the everyday practice and education

AIMS

The limbic circuit (LC) is devoted to linking emotion to behavior and cognition. The injury this system results in post-RT cognitive dysfunction. The aim of this study is to create the first radiation oncologist's practical MR-based contouring guide for the delineation of the LC for the everyday clinical practice and education.

METHODS

An anonymized diagnostic 3.0 T T1-weighted BRAVO MRI sequence from a healthy patient with typical brain anatomy was used to delineate LC. For each structure key anatomical contours were completed by radiation oncologists, along with a neuro-radiologist to generate the final version of the LC atlas.

RESULTS

a step-by-step MR-based atlas of LC was created. Key structures of the LC, such as, cingulate gyrus, fornix, septal region, mammillary bodies, thalamus and the hippocampal-amygdala formation were contoured.

CONCLUSIONS

This article provides the recommendations for the first contouring atlas of LC in the setting of patients receiving RT and education.

Particle therapy in the future of precision therapy

The first hospital-based treatment facilities for particle therapy started operation about thirty years ago. Since then, the clinical experience with protons and carbon ions has grown continuously and more than 200,000 patients have been treated to date. The promising clinical results led to a rapidly increasing number of treatment facilities and many new facilities are planned or under construction all over the world. An inverted depth-dose profile combined with potential radiobiological advantages make charged particles a precious tool for the treatment of tumours that are particularly radioresistant or located nearby sensitive structures. A rising number of trials have already confirmed the benefits of particle therapy in selected clinical situations and further improvements in beam delivery, image guidance and treatment planning are expected. This review summarises some physical and biological characteristics of accelerated charged particles and gives some examples of their clinical application. Furthermore, challenges and future perspectives of particle therapy will be discussed.

Feasibility of hippocampus-sparing VMAT for newly diagnosed glioblastoma treated by chemoradiation: pattern of failure analysis

Background

To identify the pattern of failure and oncological safety of hippocampus (HC)-sparing IMRT (HSRT) in newly diagnosed glioblastoma (GBM) patients.

Materials and methods

Eighty-two GBM patients treated with temozolomide-based chemoradiation using HSRT between 2014 and 2018 were retrospectively reviewed. HSRT consisted of a sparing of D_max of the contralateral HC < 17 Gy. Fifteen patients were unable to achieve the dose-constraints for adequate target coverage. The dose to ipsilateral HC was kept as low as possible. The pattern of failure was investigated, focusing on the area in the vicinity of the spared HC (organ and + 1 cm area). The median HSRT dose was 60 Gy in 30 fractions.

Results

The median follow-up for survivors was 11.7 months. The median progression-free and overall survival were 9.7 and 23.5 months, respectively. Six (7.3%) and eight (9.8%) patients eventually demonstrated progressive disease at the contralateral HC and HC + 1 cm, respectively. The 12-month contralateral HC and HC + 1 cm failure-free rate were 97.2 and 93.4%, respectively. However, no patient (0%) and two patients (2.4%) showed failure at contralateral HC and HC + 1 cm at initial progression, respectively. The dominant pattern of failure at the contralateral HC was by subependymal seeding (66.7%).

Conclusion

The incidence of failure at the contralateral HC and HC + 1 cm is very low and mostly accompanied by disseminated disease progression after HSRT. Since HSRT does not compromise oncological outcomes, it could be considered especially for GBM patients who are expected to have favorable survival outcomes.

Long-term outcomes and late adverse effects of a prospective study on proton radiotherapy for patients with low-grade glioma

BACKGROUND

Patients with low-grade gliomas (LGG) can survive years with their illness. Proton radiotherapy (PRT) can reduce off-target dose and decrease the risk of treatment-related morbidity. We examined long-term morbidity following proton therapy in this updated prospective cohort of patients with LGG.

METHODS

Twenty patients with LGG were enrolled prospectively and received PRT to 54 Gy(RBE) in 30 fractions. Comprehensive baseline and longitudinal assessments of toxicity, neurocognitive and neuroendocrine function, quality of life, and survival outcomes were performed up to 5 years following treatment.

RESULTS

Six patients died (all of disease) and six had progression of disease. Median follow-up was 6.8 years for the 14 patients alive at time of reporting. Median progression-free survival (PFS) was 4.5 years. Of tumors tested for molecular markers, 71% carried the IDH1-R132H mutation and 29% had 1p/19q co-deletion. There was no overall decline in neurocognitive function; however, a subset of five patients with reported cognitive symptoms after radiation therapy had progressively worse function by neurocognitive testing. Six patients developed neuroendocrine deficiencies, five of which received Dmax ≥20 Gy(RBE) to the hypothalamus-pituitary axis (HPA). Most long-term toxicities developed within 2 years after radiation therapy.

CONCLUSIONS

The majority of patients with LGG who received proton therapy retained stable cognitive and neuroendocrine function. The IDH1-R132H mutation was present in the majority, while 1p/19q loss was present in a minority. A subset of patients developed neuroendocrine deficiencies and was more common in those with higher dose to the HPA.

Cognitive impairment and morphological changes after radiation therapy in brain tumors: A review

Life expectancy of patients treated for brain tumors has lengthened due to the therapeutic improvements. Cognitive impairment has been described following brain radiotherapy, but the mechanisms leading to this adverse event remain mostly unknown. Technical evolutions aim at enhancing the therapeutic ratio. Sparing of the healthy tissues has been improved using various approaches; however, few dose constraints have been established regarding brain structures associated with cognitive functions. The aims of this literature review are to report the main brain areas involved in cognitive adverse effects induced by radiotherapy as described in literature, to better understand brain radiosensitivity and to describe potential future improvements.

Multi-institutional study of treatment patterns in Korean patients with WHO grade II gliomas: KNOG 15-02 and KROG 16-04 intergroup study

INTRODUCTION

We performed this study to identify the treatment patterns of patients with low-grade gliomas (LGG) in Korea.

METHODS

A total of 555 patients diagnosed as WHO grade II gliomas between 2000 and 2010 at 14 Korean institutions were included. The patients were divided into four adjuvant treatment groups: adjuvant fractionated radiotherapy (RT, N = 204), adjuvant chemotherapy (N = 20), adjuvant fractionated RT and chemotherapy (N = 65), and non-adjuvant treatment (N = 266) groups. We examined differences among the groups and validated patient/tumor characteristics associated with the adjuvant treatments.

RESULTS

Astrocytoma was diagnosed in 210 patients (38%), oligoastrocytoma in 85 patients (15%), and oligodendroglioma in 260 patients (47%). Gross total resection was performed in 200 patients (36%), subtotal resection in 153 (28%), partial resection in 71 patients (13%), and biopsy in 131 patients (24%). RT was most commonly applied as an adjuvant treatment. The use of chemotherapy with or without RT decreased after 2008 (from 38 to 4%). The major chemotherapeutic regimen was procarbazine, lomustine, and vincristine (PCV); however, the proportion of temozolomide increased since 2005 (up to 69%). Patient/tumor characteristics related with RT were male gender, non-seizure, multiple lobes involvement, and non-gross total resection. Chemotherapy was associated with non-gross total resection and non-astrocytoma.

CONCLUSIONS

A preference for RT and increased use of temozolomide was evident in the treatment pattern of LGG. The extent of resection was associated with a decision to perform RT and chemotherapy. To establish a robust guideline for LGG, further studies including molecular information are needed.

Hippocampus-sparing radiotherapy using volumetric modulated arc therapy (VMAT) to the primary brain tumor: the result of dosimetric study and neurocognitive function assessment

Background

We hypothesized that hippocampal-sparing radiotherapy via volumetric modulated arc therapy (VMAT) could preserve the neurocognitive function (NCF) of patients with primary brain tumors treated with radiotherapy.

Methods

We reviewed data from patients with primary brain tumors who underwent hippocampal-sparing brain radiotherapy via VMAT between February 2014 and December 2015. The optimization criteria for the contralateral hippocampus was a maximum dose (D_max) of less than 17 Gy. For NCF evaluations, the Seoul Verbal Learning Test for total recall, delayed recall, and recognition (SVLT-TR, DR, and Recognition) was performed at baseline and at seven months after radiotherapy.

Results

A total of 26 patients underwent NCF testing seven months after radiotherapy. Their median age was 49.5 years (range 26–77 years), and 14 (53.8%) had grade III/IV tumors. The median D_max to the contralateral hippocampus was 16.4 Gy (range 3.5-63.4). The median mean dose to the contralateral hippocampus, expressed as equivalent to a 2-Gy dose (EQD_2/2), was 7.4 Gy₂ (0.7–13.1). The mean relative changes in SVLT-TR, SVLT-DR, and SVLT-Recognition at seven months compared to the baseline were − 7.7% (95% confidence interval [CI], − 19.6% to 4.2%), − 9.2% (95% CI, − 25.4% to 7.0%), and − 3.4% (− 12.7% to 5.8%), respectively. Two patients (7.7%) showed deteriorated NCF in the SVLT-TR and SVLT-DR, and three (11.5%) in the SVLT-Recognition. The mean dose of the left hippocampus and bilateral hippocampi were significantly higher in patients showing deterioration of the SVLT-TR and SVLT-Recognition than in those without deterioration.

Conclusions

The contralateral hippocampus could be effectively spared in patients with primary brain tumor via VMAT to preserve the verbal memory function. Further investigation is needed to identify those patients who will most benefit from hippocampal-sparing radiotherapy of the primary brain tumor.

Electronic supplementary material

The online version of this article (10.1186/s13014-018-0975-4) contains supplementary material, which is available to authorized users.

Feasibility of Hippocampal Avoidance Radiotherapy for Glioblastoma

With improvements in survival for good performance status patients and in specific molecular subtypes of glioblastoma, some patients will survive to develop significant neurocognitive dysfunction. This retrospective planning study quantified hippocampal radiation doses in patients with glioblastoma receiving radical chemo-radiotherapy and compared this with the radiation doses that showed clinical correlation with neurocognitive dysfunction, and evaluated the potential for clinically meaningful hippocampal dose reduction using helical TomoTherapy^®.

Hippocampal sparing radiotherapy for glioblastoma patients: a planning study using volumetric modulated arc therapy

Background

The purpose of this study is to investigate the potential to reduce exposure of the contralateral hippocampus in radiotherapy for glioblastoma using volumetric modulated arc therapy (VMAT).

Methods

Datasets of 27 patients who had received 3D conformal radiotherapy (3D-CRT) for glioblastoma with a prescribed dose of 60Gy in fractions of 2Gy were included in this planning study. VMAT plans were optimized with the aim to reduce the dose to the contralateral hippocampus as much as possible without compromising other parameters. Hippocampal dose and treatment parameters were compared to the 3D-CRT plans using the Wilcoxon signed-rank test. The influence of tumour location and PTV size on the hippocampal dose was investigated with the Mann–Whitney-U-test and Spearman’s rank correlation coefficient.

Results

The median reduction of the contralateral hippocampus generalized equivalent uniform dose (gEUD) with VMAT was 36 % compared to the original 3D-CRT plans (p < 0.05). Other dose parameters were maintained or improved. The median V30Gy brain could be reduced by 17.9 % (p < 0.05). For VMAT, a parietal and a non-temporal tumour localisation as well as a larger PTV size were predictors for a higher hippocampal dose (p < 0.05).

Conclusions

Using VMAT, a substantial reduction of the radiotherapy dose to the contralateral hippocampus for patients with glioblastoma is feasible without compromising other treatment parameters. For larger PTV sizes, less sparing can be achieved. Whether this approach is able to preserve the neurocognitive status without compromising the oncological outcome needs to be investigated in the setting of prospective clinical trials.

[Guidelines for the radiotherapy of gliomas]

Gliomas are the most frequent primary brain tumours. Treating these tumours is difficult because of the proximity of organs at risk, infiltrating nature, and radioresistance. Clinical prognostic factors such as age, Karnofsky performance status, tumour location, and treatments such as surgery, radiation therapy, and chemotherapy have long been recognized in the management of patients with gliomas. Molecular biomarkers are increasingly evolving as additional factors that facilitate diagnosis and therapeutic decision-making. These practice guidelines aim at helping in choosing the best treatment, in particular radiation therapy.

Comparison between Dual Arc VMAT and 7F-IMRT in the protection of hippocampus for patients during whole brain radiotherapy

PURPOSE

The purpose of this study was to compare the dosimetric characteristics for protection of the hippocampus between dual arc VMAT (volumetric modulated arc therapy) and 7 fields intensity-modulated radiation therapy (7F-IMRT) for patients with brain metastases from lung cancer under the whole brain radiotherapy.

METHODS

Based on ten cases with brain metastases from lung cancer, two types of radiotherapy plans were designed, namely, dual arc VMAT and 7F-IMRT. Provided that the clinical requirements were satisfied, the comparisons of target dose distribution, conformity index (CI), homogeneity index (HI), dose of organs at risk (OARs), monitor units (MU) and treatment time between dual arc VMAT and 7F-IMRT were investigated for their dosimetric difference.

RESULTS

Both treatment plans met the requirements of clinical treatments. However, the PTV-HA conformity and homogeneity of dual arc VMAT were superior to those of 7F-IMRT (P < 0.05). As to OARs, the mean maximum doses (Dmax) of hippocampus, eyes and optic nerves in the dual arc VMAT plan were all lower than those in 7F-IMRT plan (P < 0.05), but the result had no statistical significance (P < 0.05) for the maximum dose of lens. Compared with 7F-IMRT, dual arc VMAT reduced the average number of MU by 67% and the average treatment time by 74%. Therefore, treatment time was shortened by dual arc VMAT.

CONCLUSION

With regards to the patients with brain metastases from lung cancer under the whole brain radiotherapy, the PTV-HA conformity and homogeneity of dual arc VMAT were superior to those of 7F-IMRT under the precise of meeting the clinical requirements. In addition, dual arc VMAT remarkably reduced the irradiation dose to OARs (hippocampus, eyes and optic nerves), MU and treatment time, as well, guaranteed patients with better protection.

A prospective study on neurocognitive effects after primary radiotherapy in high-grade glioma patients

BACKGROUND

Neurocognition is a very important aspect of a brain tumor patient's quality of life following radiotherapy. The aim of the present study was to assess neurocognitive functions of patients diagnosed with high-grade gliomas undergoing radiotherapy by using the NeuroCogFx(®) test and to examine relevant dose/volume parameters as well as patient characteristics potentially influencing the neurological baseline status and subsequent outcome.

METHODS

The cohort consisted of 44 astrocytoma World Health Organization grade III/IV patients. The NeuroCogFx(®) test was carried out on patients during (N = 44) and after (N = 21) irradiation. The test examines verbal/figural/short-term/working memory, psychomotorical speed, selective attention and verbal speed. The results were compared with regular patient and treatment data with an emphasis on the dose applied to the hippocampus.

RESULTS

Overall there were only slight changes in the median test results when comparing the baseline to the follow-up tests. In the 'verbal memory test' lower percentile ranks were achieved in left-sided tumors compared to right-sided tumors (p = 0.034). Dexamethasone intake during radiotherapy was significantly correlated with the difference between the two test batteries. Concerning figural memory, a correlation was detected between decreased figural recognition and the radiation dose to the left hippocampus (p = 0.045).

CONCLUSION

We conclude that tumor infiltration of the hippocampus has an impact on neurocognitive function. However, treatment with radiotherapy seems to have less influence on cognitive outcome than expected.

Volumetric modulated arc therapy for hippocampal-sparing radiotherapy in transformed low-grade glioma: A treatment planning case report

Timing of radiotherapy for low-grade gliomas is still controversial due to concerns of possible adverse late effects. Prevention of possible late cognitive sequelae by hippocampal avoidance has shown promise in phase II trials. A patient with progressive low-grade glioma with gradual dedifferentiation into anaplastic astrocytoma is presented along with description of radiotherapy planning process attempting to spare the hippocampus. To our knowledge, this is the first described case using volumetric modulated arc technique to spare hippocampus during transformed low-grade glioma radiotherapy. Using modern intensity-modulated radiotherapy systems it is possible to selectively spare hippocampus together with other standard organs at risk. For selected patients, an attempt to spare hippocampus can be considered as long as other dose characteristics are not significantly compromised compared to standard treatment plan created without any effort to avoid hippocampus.

Comparison of dose distributions hippocampus in high grade gliomas irradiation with linac-based imrt and volumetric arc therapy: a dosimetric study

The aim of this study was to assess the feasibility of sparing contralateral hippocampus during partial brain radiotherapy in high grade gliomas. 20 previously treated patients were replanned to 60 Gy in 30 fractions with sparing intensity-modulated radiotherapy (IMRT) and volumetric modulated arctherapy (VMAT) using the following planning objectives: 100 % of PTV covered by 95% isodose without violating organs at risk (OAR) and hot spot dose constraints. For each, standard intensity-modulated radiotherapy (IMRT) plans were generated, as well as sparing IMRT and VMAT plans which spared contralateral (hemispheric cases) hippocampus. When the three plans were compared, there was equivalent PTV coverage, homogeneity, and conformality. Sparing IMRT significantly reduced maximum, mean, V20, V30 and V40 hippocampus doses compared with standart IMRT and VMAT (p < 0.05). VMAT significantly reduced maximum left lens and mean eye doses compared with standart IMRT and sparing IMRT (p < 0.05). Brainstem, chiasm, left and right optic nerves, right eyes and lens doses were similar. VMAT significantly reduced monitor units compared with standart IMRT and sparing IMRT (p < 0.05). It is possible to spare contralateral hippocampus during PBRT for high grade gliomas using IMRT. This approach may reduce late cognitive sequelae of cranial radiotherapy.

Hippocampal EUD in primarily irradiated glioblastoma patients

BACKGROUND

Radiation delivery for malignant brain tumors is gradually becoming more precise. Particularly the possibilities of sparing adjacent normal structures such as the hippocampus are increasing. To determine its radiation exposure more exactly, the equivalent uniform dose (EUD) of the hippocampus was compared with further treatment parameters. This way sparing options could be found.

METHODS

From the database of the University hospital of Munich 61 glioblastoma patients were selected who received primary radiotherapy in 2011. General data about the etiology, treatment course, survival of the patients and dose parameters were retrieved.

RESULTS

In a linear regression analysis the side of the tumor (left hippocampus: p < 0.001/right hippocampus: p = 0.009) and its temporal location (left hippocampus: p = 0.015/right hippocampus: p = 0.033) were identified as factors with a significant influence on the EUD of the respective hippocampus. Besides this, the size of the planning target volume (PTV) and the EUD of the hippocampus correlated significantly (p = 0.027; Pearson correlation = 0.291). The median PTV size of the tumor in the right hemisphere was 386.1 ml (range 131.2-910.7 ml), and in the left hemisphere 291.3 ml (range 146.0-588.9 ml) (Kruskal-Wallis test: p = 0.048). A dose quartile analysis showed that 31 patients had a high dose exposure of the hippocampus on one side while having a moderate dose exposure in the other side.

CONCLUSIONS

The radiation exposure of the respective hippocampus is dependent on the side where the tumor is located as well as on whether it is temporally located. The exposure of the contralateral hippocampus is further dependent on multiple additional factors - nevertheless a reasonable protection seems to be possible in about half of all cases.

[Management of gliomas]

Gliomas are the most frequent primary brain tumors. Their care is difficult because of the proximity of organs at risk. The treatment of glioblastoma includes surgery followed by chemoradiation with the protocol of Stupp et al. The addition of bevacizumab allows an increase in progression-free survival by 4 months but it does not improve overall survival. This treatment is reserved for clinical trials. Intensity modulation radiotherapy may be useful to reduce the neurocognitive late effects in different types of gliomas. In elderly patients an accelerated radiotherapy 40 Gy in 15 fractions allows a similar survival to standard radiotherapy. O(6)-methylguanine-DNA methyltransferase (MGMT) status may help to choose between chemotherapy and radiotherapy. There is no standard for the treatment of recurrent gliomas. Re-irradiation in stereotactic conditions allows a median survival of 8 to 12.4 months. Anaplastic gliomas with 1p19q mutation have a greater sensibility to chemotherapy by procarbazine, lomustine and vincristine. Chemoradiotherapy in these patients has become the standard treatment. Many studies are underway testing targeted therapies, their place in the therapeutic management and new radiotherapy techniques.

Radiotherapy of high-grade gliomas: current standards and new concepts, innovations in imaging and radiotherapy, and new therapeutic approaches

The current standards in radiotherapy of high-grade gliomas (HGG) are based on anatomic imaging techniques, usually computed tomography (CT) scanning and magnetic resonance imaging (MRI). The guidelines vary depending on whether the HGG is a histological grade 3 anaplastic glioma (AG) or a grade 4 glioblastoma multiforme (GBM). For AG, T2-weighted MRI sequences plus the region of contrast enhancement in T1 are considered for the delineation of the gross tumor volume (GTV), and an isotropic expansion of 15 to 20 mm is recommended for the clinical target volume (CTV). For GBM, the Radiation Therapy Oncology Group favors a two-step technique, with an initial phase (CTV1) including any T2 hyperintensity area (edema) plus a 20 mm margin treated with up to 46 Gy in 23 fractions, followed by a reduction in CTV2 to the contrast enhancement region in T1 with an additional 25 mm margin. The European Organisation of Research and Treatment of Cancer recommends a single-phase technique with a unique GTV, which comprises the T1 contrast enhancement region plus a margin of 20 to 30 mm. A total dose of 60 Gy in 30 fractions is usually delivered for GBM, and a dose of 59.4 Gy in 33 fractions is typically given for AG. As more than 85% of HGGs recur in field, dose-escalation studies have shown that 70 to 75 Gy can be delivered in 6 weeks with relevant toxicities developing in < 10% of the patients. However, the only randomized dose-escalation trial, in which the boost dose was guided by conventional MRI, did not show any survival advantage of this treatment over the reference arm. HGGs are amongst the most infiltrative and heterogeneous tumors, and it was hypothesized that the most highly aggressive areas were missed; thus, better visualization of these high-risk regions for radiation boost could decrease the recurrence rate. Innovations in imaging and linear accelerators (LINAC) could help deliver the right doses of radiation to the right subvolumes according to the dose-painting concept. Advanced imaging techniques provide functional information on cellular density (diffusion MRI), angiogenesis (perfusion MRI), metabolic activity and cellular proliferation [positron emission tomography (PET) and magnetic resonance spectroscopy (MRS)]. All of these non-invasive techniques demonstrated good association between the images and histology, with up to 40% of HGGs functionally presenting a high activity within the non-contrast-enhanced areas in T1. New LINAC technologies, such as intensity-modulated and stereotactic radiotherapy, help to deliver a simultaneous integrated boost (SIB) > 60 Gy. Trials delivering a SIB into a biological GTV showed the feasibility of this treatment, but the final results, in terms of clinical benefits for HGG patients, are still pending. Many issues have been identified: the variety of MRI and PET machines (and amino-acid tracers), the heterogeneity of the protocols used for image acquisition and post-treatment, the geometric distortion and the unreliable algorithms for co-registration of brain anatomy with functional maps, and the semi-quiescent but highly invasive HGG cells. These issues could be solved by the homogenization of the protocols and software applications, the simultaneous acquisition of anatomic and functional images (PET-MRI machines), the combination of complementary imaging tools (perfusion and diffusion MRI), and the concomitant addition of some ad hoc targeted drugs against angiogenesis and invasiveness to chemoradiotherapy. The integration of these hybrid data will construct new synthetic metrics for fully individualized treatments.

Sparing functional anatomical structures during intensity-modulated radiotherapy: an old problem, a new solution

ABSTRACT During intensity-modulated radiotherapy, an organ is usually assumed to be functionally homogeneous and, generally, its anatomical and spatial heterogeneity with respect to radiation response are not taken into consideration. However, advances in imaging and radiation techniques as well as an improved understanding of the radiobiological response of organs have raised the possibility of sparing the critical functional structures within various organs at risk during intensity-modulated radiotherapy. Here, we discuss these structures, which include the critical brain structure, or neural nuclei, and the nerve fiber tracts in the CNS, head and neck structures related to radiation-induced salivary and swallowing dysfunction, and functional structures in the heart and lung. We suggest that these structures can be used as potential surrogate organs at risk in order to minimize their radiation dose and/or irradiated volume without compromising the dose coverage of the target volume during radiation treatment.

Why and how to spare the hippocampus during brain radiotherapy: the developing role of hippocampal avoidance in cranial radiotherapy

The goal of this review is to summarize the rationale for and feasibility of hippocampal sparing techniques during brain irradiation. Radiotherapy is the most effective non-surgical treatment of brain tumors and with the improvement in overall survival for these patients over the last few decades, there is an effort to minimize potential adverse effects leading to possible worsening in quality of life, especially worsening of neurocognitive function. The hippocampus and associated limbic system have long been known to be important in memory formation and pre-clinical models show loss of hippocampal stem cells with radiation as well as changes in architecture and function of mature neurons. Cognitive outcomes in clinical studies are beginning to provide evidence of cognitive effects associated with hippocampal dose and the cognitive benefits of hippocampal sparing. Numerous feasibility planning studies support the feasibility of using modern radiotherapy systems for hippocampal sparing during brain irradiation. Although results of the ongoing phase II and phase III studies are needed to confirm the benefit of hippocampal sparing brain radiotherapy on neurocognitive function, it is now technically and dosimetrically feasible to create hippocampal sparing treatment plans with appropriate irradiation of target volumes. The purpose of this review is to provide a brief overview of studies that provide a rationale for hippocampal avoidance and provide summary of published feasibility studies in order to help clinicians prepare for clinical usage of these complex and challenging techniques.

Prophylactic cranial irradiation: 5 years on

With advances in cancer management, patients are living with the long-term sequelae of both cancer and its treatment. This era of cancer survivorship poses unique challenges to the interdisciplinary cancer team in terms of management and prevention of treatment-related toxicities. This paper describes the case of a 55-year-old patient with neurocognitive disturbance as a result of prophylactic cranial irradiation (PCI). Five years after a diagnosis of small cell lung cancer, she is now an inpatient at a specialist palliative care unit. The current evidence for PCI and for potentially modifiable risk factors for neurocognitive disturbance as a consequence of PCI is explored.

Is current technology improving outcomes with radiation therapy for gliomas?

Radiotherapy (RT) remains the principal component of glioma treatment, and three-dimensional conformal RT (3DCRT) is the current standard of RT delivery. Advances in imaging and in RT technology have enabled more precise treatment to defined targets combined with better means of avoiding critical normal structures, and this is complemented by intensive quality assurance, which includes on-treatment imaging. The refinements of 3DCRT include intensity modulated RT (IMRT), arcing IMRT, and high-precision conformal RT, formerly described as "stereotactic," which can be delivered using a linear accelerator or other specialized equipment. Although proton therapy uses heavy charged particles, the principal application can also be considered as refinement of 3DCRT. The technologies generally improve the dose differential between the tumor and normal tissue and enable more dose-intensive treatments. However, these have not translated into improved survival outcome in patients with low- and high-grade gliomas. More intensive altered fractionation regimens have also failed to show survival benefit. Nevertheless, novel technologies enable better sparing of normal tissue and selective avoidance of critical structures, and these need to be explored further to improve the quality of life of patients with gliomas. Principal clinical advance in RT has been the recognition that less intensive treatments are beneficial for patients with adverse prognosis high-grade gliomas. We conclude that the principal gain of modern RT technology is more likely to emerge as a reduction in treatment related toxicity rather than as an improvement in overall survival; the optimal avoidance strategies remain to be defined.

Hippocampal-sparing radiotherapy: the new standard of care for World Health Organization grade II and III gliomas?

The neurocognitive effects of cranial radiotherapy in patients with gliomas are well-recognised and may be related to the dose delivered to the hippocampi. Intensity modulated radiotherapy (IMRT) is a radiotherapy technique that can be used to selectively spare the hippocampi without compromising the dose delivered to the tumour. This study aimed to evaluate if hippocampal-sparing IMRT is achievable in patients with World Health Organization (WHO) grade II and III gliomas. A retrospective review of consecutive patients with WHO grade II and III gliomas treated with IMRT at our institution between January 2009 and August 2012 was performed. Hippocampal-sparing was defined as a mean dose to at least one hippocampus of less than 30 Gy. The dose delivered to the tumour was never compromised to achieve the hippocampal dose constraint. Logistic regression analyses were performed to identify predictive factors for achieving hippocampal-sparing treatment. Eighteen patients were identified and hippocampal-sparing was achieved in 14 (78%). The median dose prescribed was 59.4 Gy in 33 fractions and 11 patients had WHO grade III gliomas. The mean dose to the contralateral hippocampus was 24.9 Gy. Planning target volumes less than 420.5 cm3 were more likely to enable hippocampal-sparing treatment to be given (hazard ratio 1.7, p=0.03) and there was a trend with oligodendrogliomas and anaplastic oligodendrogliomas. Hippocampal-sparing radiotherapy is feasible in patients with WHO grade II and III gliomas. Oncologic outcomes are yet to be assessed prospectively. The relationship between hippocampal dose and neurocognitive function in adults is currently under investigation.

Subventricular zone localized irradiation affects the generation of proliferating neural precursor cells and the migration of neuroblasts

Radiation therapy is a part of the standard treatment for brain tumor patients, often resulting in irreversible neuropsychological deficits. These deficits may be due to permanent damage to the neural stem cell (NSC) niche, damage to local neural progenitors, or neurotoxicity. Using a computed tomography-guided localized radiation technique, we studied the effects of radiation on NSC proliferation and neuroblast migration in the mouse brain. Localized irradiation of the subventricular zone (SVZ) eliminated the proliferating neural precursor cells and migrating neuroblasts. After irradiation, type B cells in the SVZ lacked the ability to generate migrating neuroblasts. Neuroblasts from the unirradiated posterior SVZ did not follow their normal migratory path through the irradiated anterior SVZ. Our results indicate that the migrating neuroblasts were not replenished, despite the presence of type B cells in the SVZ post-irradiation. This study provides novel insights into the effects of localized SVZ radiation on neurogenesis and cell migration that may potentially lead to the development of new radiotherapy strategies to minimize damage to NSCs and neuroblast migration.

Regional variation in brain white matter diffusion index changes following chemoradiotherapy: a prospective study using tract-based spatial statistics

Purpose

There is little known about how brain white matter structures differ in their response to radiation, which may have implications for radiation-induced neurocognitive impairment. We used diffusion tensor imaging (DTI) to examine regional variation in white matter changes following chemoradiotherapy.

Methods

Fourteen patients receiving two or three weeks of whole-brain radiation therapy (RT) ± chemotherapy underwent DTI pre-RT, at end-RT, and one month post-RT. Three diffusion indices were measured: fractional anisotropy (FA), radial diffusivity (RD), and axial diffusivity (AD). We determined significant individual voxel changes of diffusion indices using tract-based spatial statistics, and mean changes of the indices within fourteen white matter structures of interest.

Results

Voxels of significant FA decreases and RD increases were seen in all structures (p<0.05), with the largest changes (20–50%) in the fornix, cingula, and corpus callosum. There were highly significant between-structure differences in pre-RT to end-RT mean FA changes (p<0.001). The inferior cingula had a mean FA decrease from pre-RT to end-RT significantly greater than 11 of the 13 other structures (p<0.00385).

Conclusions

Brain white matter structures varied greatly in their response to chemoradiotherapy as measured by DTI changes. Changes in FA and RD related to white matter demyelination were prominent in the cingula and fornix, structures relevant to radiation-induced neurocognitive impairment. Future research should evaluate DTI as a predictive biomarker of brain chemoradiotherapy adverse effects.

Use of a deformable atlas to identify cryptic critical structures in the treatment of glioblastoma multiforme

Dose constraints for traditional neural critical structures (e.g. optic chiasm, brain stem) are a standard component of planning radiation therapy to the central nervous system. Increasingly, investigators are becoming interested in accounting for the dose delivered to other non-target neural structures (e.g. hippocampi), which are not easily identified on axial imaging. In this pilot study, a commercially available digital atlas was used to identify cryptic neural structures (hippocampus, optic radiations, and visual cortices) in 6 patients who received intensity modulated radiation therapy (IMRT) as part of multimodal management of glioblastoma multiforme (GBM). The patient's original IMRT plans were re-optimized, with avoidance parameters for the newly identified critical structures. Re-optimization was able to reduce both mean and maximum dose to the volumes of interest, with a more pronounced effect for contralateral structures. Mean dose was reduced by 11% and 3% to contralateral and ipsilateral structures, respectively, with comparable reduction in maximum dose of 10% and 2%, respectively. Importantly, target coverage was not compromised, with an average change in coverage of 0.2%. Overall, our results demonstrate the feasibility of incorporating tools for cryptic critical structure identification into the treatment planning process for GBM.

Gamma Knife, CyberKnife, TomoTherapy: gadgets or useful tools?

PURPOSE OF REVIEW

This review provides information and an update on stereotactic radiosurgery (SRS) equipment, with a focus on intracranial lesions and brain neoplasms.

RECENT FINDINGS

Gamma Knife radiosurgery represents the gold standard for intracranial radiosurgery, using a dedicated equipment, and has recently evolved with a newly designed technology, Leksell Gamma Knife Perfexion. Linear accelerator-based radiosurgery is more recent, and originally based on existing systems, either adapted or dedicated to radiosurgery. Equipment incorporating specific technologies, such as the robotic CyberKnife system, has been developed. Novel concepts in radiation therapy delivery techniques, such as intensity-modulated radiotherapy, were also developed; their integration with computed tomography imaging and helical delivery has led to the TomoTherapy system. Recent data on the management of intracranial tumors with radiosurgery illustrate the trend toward a larger use and acceptance of this therapeutic modality.

SUMMARY

SRS has become an important alternative treatment for a variety of lesions. Each radiosurgery system has its advantages and limitations. The 'perfect' and ubiquitous system does not exist. The choice of a radiosurgery system may vary with the strategy and needs of specific radiosurgery programs. No center can afford to acquire every technology, and strategic choices have to be made. Institutions with large neurosurgery and radiation oncology programs usually have more than one system, allowing optimization of the management of patients with a choice of open neurosurgery, radiosurgery, and radiotherapy. Given its minimally invasive nature and increasing clinical acceptance, SRS will continue to progress and offer new advances as a therapeutic tool in neurosurgery and radiotherapy.