Outcomes of diffusion tensor tractography-integrated stereotactic radiosurgery

Evaluation of inverse treatment planning for gamma knife radiosurgery using fMRI brain activation maps as organs at risk

BACKGROUND

Stereotactic radiosurgery (SRS) can be an effective primary or adjuvant treatment option for intracranial tumors. However, it carries risks of various radiation toxicities, which can lead to functional deficits for the patients. Current inverse planning algorithms for SRS provide an efficient way for sparing organs at risk (OARs) by setting maximum radiation dose constraints in the treatment planning process.

PURPOSE

We propose using activation maps from functional MRI (fMRI) to map the eloquent regions of the brain and define functional OARs (fOARs) for Gamma Knife SRS treatment planning.

METHODS

We implemented a pipeline for analyzing patient fMRI data, generating fOARs from the resulting activation maps, and loading them onto the GammaPlan treatment planning software. We used the Lightning inverse planner to generate multiple treatment plans from open MRI data of five subjects, and evaluated the effects of incorporating the proposed fOARs.

RESULTS

The Lightning optimizer designs treatment plans with high conformity to the specified parameters. Setting maximum dose constraints on fOARs successfully limits the radiation dose incident on them, but can have a negative impact on treatment plan quality metrics. By masking out fOAR voxels surrounding the tumor target it is possible to achieve high quality treatment plans while controlling the radiation dose on fOARs.

CONCLUSIONS

The proposed method can effectively reduce the radiation dose incident on the eloquent brain areas during Gamma Knife SRS of brain tumors.

Application of diffusion tensor-based tractography in treatment of brain arteriovenous malformations: a systematic review

There is no systematic review investigating the utility of Diffusion tensor-based tractography findings for treating brain arteriovenous malformations (bAVMs). This systematic review aims to investigate the outcomes following bAVM treatment when tractography data is incorporated into treatment planning. PubMed/MEDLINE, Scopus, and Cochrane Library, were searched for published studies. Prospective or retrospective studies involving at least one patient with confirmed bAVM and available data on tractography and clinical outcomes were included. A total of 16 studies were eligible for this review, consisting of 298 patients. 48.2% of patients were female. The mean age of the patients was 27.5 years (range: 5-77). Stereotactic radiosurgery (SRS) and microsurgical resection each were the treatment of choice in eight studies, respectively. Two-hundred forty-eight patients underwent SRS as the primary treatment, while microsurgery was used to resect the bAVMs in 50 patients. The corticospinal tract, optic pathway, and arcuate fasciculus were the most widely investigated white matter tracts. Tractography disruption and failure frequencies were 19.1% and 1.8%, respectively. The pooled proportions (95% CI) of obliteration rates were 88.78% (73.51-95.76) for microsurgery and 51.45% (13-17-88.10) following SRS. Treatment-related non-hemorrhagic complications rates occurred in 24.2% and 9.9% of patients who underwent microsurgical resection and SRS, respectively. Tractography findings can contribute to providing a more accurate dosimetry analysis of functional white matter tracts at risk prior to SRS and minimizing the surgical morbidity following microsurgical resection.

Conservation of pyramidal tract in radiosurgery for brain metastases of lung adenocarcinoma: Three-dimensional analysis of biologically effective dose

BACKGROUND

Gamma knife surgery (GKS) for brain metastases (BMs) adjacent to the pyramidal tract (PT) is still a challenge to conduct. PT visualization and biologically effective dose (BED) calculation on a voxel-by-voxel basis may provide data to establish clinically safe values. We aimed to assess the relationship of parameters extracted from the BED-volume histogram with outcomes of PT after GKS-treating target (adjacent BM of lung adenocarcinoma).

METHODS

We formed BED-volume histograms for 672 BMs in a retrospective cohort, using 3-dimensional (3D) coordinate values of PT, target, and each iso-centre to calculate the 3D BED distribution in a 200 × 200 × 200 matrix. PT conservation failure (PTCF) was judged clinically and radiologically and classified as lesion progression and radionecrosis. Cox proportional hazards models were used to analyse 3D BED parameters. Internal validation of models was performed by bootstrapping.

RESULTS

There were 116 (17.3 %) subjects with PTCF in the cohort, of which 74 (11.0 %) and 42 (6.3 %) were caused by lesion progression and radionecrosis, respectively. Multivariate analysis showed that D_{Lesion_min} BED and D_{Lesion_90%} BED significantly predicted lesion progression (P <.001). D_{PT_Max} BED and V_{PT_ BED40} significantly predicted radionecrosis (P <.001). The model predicting PTCF showed fair discrimination and calibration of D_{Lesion_min} BED + D_{Lesion_90%} BED and D_{PT_Max} BED + V_{PT_ BED40}.

CONCLUSIONS

The conservation of PT in GKS for BMs of lung adenocarcinoma depends on the combination of PT-tolerated BED and target effective control BED. Therefore, a BED-volume histogram with a 3D BED algorithm is proposed to assess plan quality.

Radiosurgery imaging

The most important imaging technology for GKNS continues to be magnetic resonance. The introduction of 3 Tesla machines permits quicker studies with better signal to noise ratio. The more powerful magnet increases the chances of heating the points of contact between patient and frame, but this has been solved with non-conducting nuts. There are several sequences for special functions. CISS studies are optimal for demonstrating cranial nerves in their passage through the subarachnoid space. FLAIR studies facilitate the distinction between CSF and edema due to inflammation. DTI permits the visualization of nerve fiber tracts. This has at least two current applications. In treatment planning of visible lesions, DTI permits a more efficient avoidance of important tracts. In functional work, tracts can be used to improve the definition of functional targets. Non stereotactic MRI can be imported into GammaPlan and co-registered to a non-distorted CT image.

Is Diffusion Tensor Imaging-Guided Radiotherapy the New State-of-the-Art? A Review of the Current Literature and Technical Insights

Despite the increasing precision of radiotherapy delivery, it is still frequently associated with neurological complications. This is in part due to damage to eloquent white matter (WM) tracts, which is made more likely by the fact they cannot be visualised on standard structural imaging. WM is additionally more vulnerable than grey matter to radiation damage. Primary brain malignancies also are known to spread along the WM. Diffusion tensor imaging (DTI) is the only in vivo method of delineating WM tracts. DTI is an imaging technique that models the direction of diffusion and therefore can infer the orientation of WM fibres. This review article evaluates the current evidence for using DTI to guide intracranial radiotherapy and whether it constitutes a new state-of-the-art technique. We provide a basic overview of DTI and its known applications in radiotherapy, which include using tractography to reduce the radiation dose to eloquent WM tracts and using DTI to detect or predict tumoural spread. We evaluate the evidence for DTI-guided radiotherapy in gliomas, metastatic disease, and benign conditions, finding that the strongest evidence is for its use in arteriovenous malformations. However, the evidence is weak in other conditions due to a lack of case-controlled trials.

Tractography methods and findings in brain tumors and traumatic brain injury

White matter fiber tracking using diffusion magnetic resonance imaging (dMRI) provides a noninvasive approach to map brain connections, but improving anatomical accuracy has been a significant challenge since the birth of tractography methods. Utilizing tractography in brain studies therefore requires understanding of its technical limitations to avoid shortcomings and pitfalls. This review explores tractography limitations and how different white matter pathways pose different challenges to fiber tracking methodologies. We summarize the pros and cons of commonly-used methods, aiming to inform how tractography and its related analysis may lead to questionable results. Extending these experiences, we review the clinical utilization of tractography in patients with brain tumors and traumatic brain injury, starting from tensor-based tractography to more advanced methods. We discuss current limitations and highlight novel approaches in the context of these two conditions to inform future tractography developments.

Clinical applications of magnetic resonance imaging based functional and structural connectivity

Advances in computational neuroimaging techniques have expanded the armamentarium of imaging tools available for clinical applications in clinical neuroscience. Non-invasive, in vivo brain MRI structural and functional network mapping has been used to identify therapeutic targets, define eloquent brain regions to preserve, and gain insight into pathological processes and treatments as well as prognostic biomarkers. These tools have the real potential to inform patient-specific treatment strategies. Nevertheless, a realistic appraisal of clinical utility is needed that balances the growing excitement and interest in the field with important limitations associated with these techniques. Quality of the raw data, minutiae of the processing methodology, and the statistical models applied can all impact on the results and their interpretation. A lack of standardization in data acquisition and processing has also resulted in issues with reproducibility. This limitation has had a direct impact on the reliability of these tools and ultimately, confidence in their clinical use. Advances in MRI technology and computational power as well as automation and standardization of processing methods, including machine learning approaches, may help address some of these issues and make these tools more reliable in clinical use. In this review, we will highlight the current clinical uses of MRI connectomics in the diagnosis and treatment of neurological disorders; balancing emerging applications and technologies with limitations of connectivity analytic approaches to present an encompassing and appropriate perspective.

MRI-based brain structural changes following radiotherapy of Nasopharyngeal Carcinoma: A systematic review

PURPOSE

Nasopharyngeal carcinoma (NPC) radiotherapy (RT) irradiates parts of the brain which may cause cerebral tissue changes. This study aimed to systematically review the brain microstructure changes using MRI-based measures, diffusion tensor imaging (DTI), diffusion kurtosis imaging (DKI) and voxel-based morphometry (VBM) and the impact of dose and latency following RT.

METHODS

PubMed and Scopus databases were searched based on PRISMA guideline to determine studies focusing on changes following NPC RT.

RESULTS

Eleven studies fulfilled the inclusion criteria. Microstructural changes occur most consistently in the temporal region. The changes were correlated with latency in seven studies; fractional anisotropy (FA) and gray matter (GM) volume remained low even after a longer period following RT and areas beyond irradiation site with reduced FA and GM measures. For dosage, only one study showed correlation, thus requiring further investigations.

CONCLUSION

DTI, DKI and VBM may be used as a surveillance tool in detecting brain microstructural changes of NPC patients which correlates to latency and brain areas following RT.

A preliminary study on the application of DTI in the treatment of brain tumors in motor function areas with gamma knife

OBJECTIVES

The treatment safety and efficiency as well as the life quality of patients are still main concerns in gamma knife radiosurgery. In this study, the feasibility of applying diffusion tensor imaging (DTI) in gamma knife radiosurgery for the treatment of brain tumor in motor function areas was investigated, which aims to provide protection on the pyramidal tract and preserve the motor function in patients.

PATIENTS AND METHODS

Total 74 patients with solid brain tumor were enrolled and divided into DTI group and control group. The tumor control rate was assessed at 3 months after surgery. The muscle strength of affected limb, KPS scores, ZEW scores and complications were evaluated at 3 and 6 months after gamma knife radiosurgery.

RESULTS

Our results indicated that the tumor control rate, complication rate, the muscle strength of affected limb and KPS scores were not significantly different between the two groups at 3 months after surgery. At 6 months after gamma knife radiosurgery, the complication rate (0% vs 50 %, P = 0.044), KPS scores (64.9 % vs 37.8 %, P = 0.036) and ZEW scores (78.4 % vs 54.1 %, P = 0.044) of DTI group were better than the control group. Furthermore, the stability of muscle strength in patients with limb dysfunction was significantly improved in DTI group (86.4 % vs 50 %, P = 0.028).

CONCLUSION

In summary, the application of DTI in gamma knife radiosurgery for the treatment of brain tumors in motor function areas can precisely define the tumor edge from pyramidal tract, which will support on designing individual treatment plan, reducing the incidence of complications, and improving long-term life quality in patients.

Integrating navigated transcranial magnetic stimulation motor mapping in hypofractionated and single-dose gamma knife radiosurgery: A two-patient case series and a review of literature

Background:

The aim of the study was to demonstrate the feasibility of integrating navigated transcranial magnetic stimulation (nTMS) in preoperative gamma knife radiosurgery (GKRS) planning of motor eloquent brain tumors.

Case Description:

The first case was a 53-year-old female patient with metastatic breast cancer who developed focal epileptic seizures and weakness of the left hand. The magnetic resonance imaging (MRI) scan demonstrated a 30 mm metastasis neighboring the right precentral gyrus and central sulcus. The lesion was treated with adaptive hypofractionated GKRS following preoperative nTMS-based motor mapping. Subsequent follow-up imaging (up to 12 months) revealed next to complete tumor ablation without toxicity. The second case involved a previously healthy 73-year-old male who similarly developed new left-handed weakness. A subsequent MRI demonstrated a 26 mm metastatic lesion, located in the right postcentral gyrus and 5 mm from the hand motor area. The extracranial screening revealed a likely primary lung adenocarcinoma. The patient underwent preoperative nTMS motor mapping prior to treatment. Perilesional edema was noted 6 months postradiosurgery; nevertheless, long- term tumor control was demonstrated. Both patients experienced motor function normalization shortly after treatment, continuing to final follow-up.

Conclusion:

Integrating preoperative nTMS motor mapping in treatment planning allowed us to reduce dose distributions to perilesional motor fibers while achieving salvage of motor function, lasting seizure freedom, and tumor control. These initial data along with our review of the available literature suggest that nTMS can be of significant assistance in brain radiosurgery. Prospective studies including larger number of patients are still warranted.

Re-Evaluation of the Size Limitation in Single-Session Stereotactic Radiosurgery for Brain Arteriovenous Malformations: Detailed Analyses on the Outcomes with Focusing on Radiosurgical Doses

BACKGROUND

Single-session stereotactic radiosurgery (SRS) for large arteriovenous malformations (AVMs) ≥10 mL remains controversial, which is considered as the current size limitation.

OBJECTIVE

To reconsider the size limitation of SRS for AVMs by profoundly analyzing dose-volume relationship.

METHODS

Data on 610 consecutive patients with AVM treated with SRS using regular (18-22 Gy) or low (&lt;18 Gy) prescription doses were retrospectively analyzed. AVMs were classified into 4 groups: small (&lt;5 mL), medium (≥5 and &lt;10 mL), medium-large (≥10 and &lt;15 mL), and large (≥15 mL). The maximum volumes were 22.5 mL (regular-dose group) and 23.5 mL (low-dose group).

RESULTS

When treated with regular doses, the cumulative 6-yr obliteration rates for each of the 4 AVM groups were 86%, 80%, 87%, and 79%, respectively; the cumulative 10-yr significant neurological event (SNE) rates were 2.6%, 3.9%, 6.8%, and 5.3%, respectively. Regarding large AVMs, regular-dose SRS resulted in marginally better obliteration rate (6-yr cumulative rate, 79% vs 48%, P = .111) and significantly lower SNE (5-yr cumulative rate, 5% vs 31%, P = .038) and post-SRS hemorrhage rate (8-yr cumulative rate, 0% vs 54%, P = .002) compared to low-dose SRS. Multivariate analyses revealed that regular-dose SRS significantly contributed to increase in the obliteration rate and decrease in SNEs and hemorrhage.

CONCLUSION

The outcomes for large AVMs were generally favorable when treated with ablative doses. Single-session SRS could be acceptable for AVMs up to ≈20 mL if treated with ablative doses.

Diffusion Tensor Imaging for Ruptured Cerebral Arteriovenous Malformation

Non-ruptured arteriovenous malformations (AVMs) rarely cause tract disruption. Few studies have described how ruptured AVMs influence white matter (WM) tract morphology. We reviewed consecutive AVM cases treated at a tertiary care hospital where diffusion tensor imaging (DTI) tractography was obtained preoperatively. DTI was performed using the Synaptive Plan (Synaptive Medical Inc., Toronto, Canada). Quality control was performed by clinical application specialist. Perinidal fractional anisotropy (FA) value of corticospinal tracts (CST) was obtained. A reference FA value was obtained from the corresponding area on the contralateral side. Images were evaluated by a consultant neuroradiologist. Radiological findings were correlated with clinical findings. White matter morphology was described by a consultant neuroradiologist. All three cases included in the study had a history of haemorrhage in the past. Two patients had disruption of CST and presented with a significant neurological deficit. In one patient FA value of CST around the nidus was comparable to the contralateral side and did not show any neurological deficit. DTI integrated neuronavigation was used to plan the trajectory and complete resection of the AVM with excellent postoperative recovery.

Quantification of the radiation dose to the pyramidal tract using tractography in treatment planning for stereotactic radiosurgery

In stereotactic radiosurgery for intracranial lesions, optimization of the dose to the at-risk organs is important to avoid neurological complications. We aimed to quantify the dose to the pyramidal tract (PT) and improve treatment planning for gamma knife radiosurgery by combining tractography. Pyramidal tractography images were depicted in 23 patients with lesions adjacent to the PT and fused with stereotactic magnetic resonance images. We regarded the PT as an at-risk organ and performed dose planning. To assess the efficacy of this process, we compared clinical parameters between plans with and without tractography. In the plans with tractography, the maximum PT dose was significantly reduced, although the irradiation time was prolonged by 3.5 min. There was no significant difference in the dose covering 95% of the lesion volume (D95). This result suggests that the PT dose can be reduced while maintaining the D95 with clinically acceptable prolongation of the irradiation time.

White matter tractography for neurosurgical planning: A topography-based review of the current state of the art

We perform a review of the literature in the field of white matter tractography for neurosurgical planning, focusing on those works where tractography was correlated with clinical information such as patient outcome, clinical functional testing, or electro-cortical stimulation. We organize the review by anatomical location in the brain and by surgical procedure, including both supratentorial and infratentorial pathologies, and excluding spinal cord applications. Where possible, we discuss implications of tractography for clinical care, as well as clinically relevant technical considerations regarding the tractography methods. We find that tractography is a valuable tool in variable situations in modern neurosurgery. Our survey of recent reports demonstrates multiple potentially successful applications of white matter tractography in neurosurgery, with progress towards overcoming clinical challenges of standardization and interpretation.

Radiotherapy planning using MRI

The use of magnetic resonance imaging (MRI) in radiotherapy (RT) planning is rapidly expanding. We review the wide range of image contrast mechanisms available to MRI and the way they are exploited for RT planning. However a number of challenges are also considered: the requirements that MR images are acquired in the RT treatment position, that they are geometrically accurate, that effects of patient motion during the scan are minimized, that tissue markers are clearly demonstrated, that an estimate of electron density can be obtained. These issues are discussed in detail, prior to the consideration of a number of specific clinical applications. This is followed by a brief discussion on the development of real-time MRI-guided RT.

The long-term outcomes of radiosurgery for arteriovenous malformations in pediatric and adolescent populations

OBJECT Although stereotactic radiosurgery (SRS) has been accepted as a therapeutic option for arteriovenous malformations (AVMs) in children and adolescents, substantial data are still lacking regarding the outcomes of SRS for AVMs in this age group, especially long-term complications. This study aimed to clarify the long-term outcomes of SRS for the treatment of AVM in pediatric patients aged ≤ 18 years. METHODS Outcomes of 116 patients who were aged 4-18 years when they underwent SRS between 1990 and 2009 at the study institute were analyzed retrospectively. RESULTS The median follow-up period after SRS was 100 months, with 6 patients followed up for more than 20 years. Actuarial obliteration rates at 3 and 5 years after SRS were 68% and 88%, respectively. Five hemorrhages occurred in 851 patient-years of follow-up. The annual bleeding rate after SRS before obliteration was calculated as 1.3%, which decreased to 0.2% after obliteration. Shorter maximum nidus diameter (p = 0.02) and higher margin dose (p = 0.03) were associated with a higher obliteration rate. Ten patients experienced adverse events after SRS. Of them, 4 patients presented with delayed complications years after SRS (range 9-20 years after SRS). CONCLUSIONS SRS can reduce the risk of hemorrhage in pediatric and adolescent AVMs, with an acceptable risk of complications in the long term. However, adverse events such as expanding hematoma and radiation necrosis that can occur after substantial follow-up should be taken into account at the time that treatment decisions are made and informed consent is obtained.

Quantitative Imaging in Radiation Oncology: An Emerging Science and Clinical Service

Radiation oncology has long required quantitative imaging approaches for the safe and effective delivery of radiation therapy. The past 10 years has seen a remarkable expansion in the variety of novel imaging signals and analyses that are starting to contribute to the prescription and design of the radiation treatment plan. These include a rapid increase in the use of magnetic resonance imaging, development of contrast-enhanced imaging techniques, integration of fluorinated deoxyglucose-positron emission tomography, evaluation of hypoxia imaging techniques, and numerous others. These are reviewed with an effort to highlight challenges related to quantification and reproducibility. In addition, several of the emerging applications of these imaging approaches are also highlighted. Finally, the growing community of support for establishing quantitative imaging approaches as we move toward clinical evaluation is summarized and the need for a clinical service in support of the clinical science and delivery of care is proposed.

Evaluating contextual processing in diffusion MRI: application to optic radiation reconstruction for epilepsy surgery

Diffusion MRI and tractography allow for investigation of the architectural configuration of white matter in vivo, offering new avenues for applications like presurgical planning. Despite the promising outlook, there are many pitfalls that complicate its use for (clinical) application. Amongst these are inaccuracies in the geometry of the diffusion profiles on which tractography is based, and poor alignment with neighboring profiles. Recently developed contextual processing techniques, including enhancement and well-posed geometric sharpening, have shown to result in sharper and better aligned diffusion profiles. However, the research that has been conducted up to now is mainly of theoretical nature, and so far these techniques have only been evaluated by visual inspection of the diffusion profiles. In this work, the method is evaluated in a clinically relevant application: the reconstruction of the optic radiation for epilepsy surgery. For this evaluation we have developed a framework in which we incorporate a novel scoring procedure for individual pathways. We demonstrate that, using enhancement and sharpening, the extraction of an anatomically plausible reconstruction of the optic radiation from a large amount of probabilistic pathways is greatly improved in three healthy controls, where currently used methods fail to do so. Furthermore, challenging reconstructions of the optic radiation in three epilepsy surgery candidates with extensive brain lesions demonstrate that it is beneficial to integrate these methods in surgical planning.

An introduction to molecular imaging in radiation oncology: a report by the AAPM Working Group on Molecular Imaging in Radiation Oncology (WGMIR)

Molecular imaging is the direct or indirect noninvasive monitoring and recording of the spatial and temporal distribution of in vivo molecular, genetic, and/or cellular processes for biochemical, biological, diagnostic, or therapeutic applications. Molecular images that indicate the presence of malignancy can be acquired using optical, ultrasonic, radiologic, radionuclide, and magnetic resonance techniques. For the radiation oncology physicist in particular, these methods and their roles in molecular imaging of oncologic processes are reviewed with respect to their physical bases and imaging characteristics, including signal intensity, spatial scale, and spatial resolution. Relevant molecular terminology is defined as an educational assist. Current and future clinical applications in oncologic diagnosis and treatment are discussed. National initiatives for the development of basic science and clinical molecular imaging techniques and expertise are reviewed, illustrating research opportunities in as well as the importance of this growing field.

Advanced Image Coregistration within the Leksell Workstation for the Planning of Glioma Surgery: Initial Experience

Background Leksell GammaPlan (LGP) and SurgiPlan (ELEKTA Instruments AB, Stockholm, Sweden) may be used effectively for the detailed evaluation of regional neuroanatomy before open neurosurgical procedures. We report our initial experience in the cases of cerebral gliomas. Methods LGP v.8.3 was used before the surgical resection of cerebral gliomas for (1) the delineation of subdural grid electrodes and a detailed evaluation of their position relatively to cortical structures, and (2) for the fusion of structural magnetic resonance imaging and diffusion tensor imaging (DTI) for a detailed visualization of the corticospinal tract (CST) and optic radiation. Results Delineation of the subdural grid within LGP in a patient with seizures caused by left parietal glioma permitted a detailed assessment of the location of electrodes relative to the cortical gyri and sulci and significantly facilitated interpretation of brain mapping before tumor resection. In another patient with parieto-occipital glioma, simultaneous three-dimensional visualization of the tumor, CST, and optic radiation with the use of LGP permitted us to perform tumor resection without postoperative neurologic complications. Finally, incorporation of DTI into SurgiPlan resulted in precise planning of stereotactic biopsy for bilateral thalamic glioma. Conclusion The possibility for detailed evaluation of regional neuroanatomy based on various images within LGP and SurgiPlan may facilitate effective and safe surgical management of intracranial gliomas.

Diffusion tensor imaging of the spinal cord: a review

Diffusion tensor imaging (DTI) is a magnetic resonance technique capable of measuring the magnitude and direction of water molecule diffusion in various tissues. The use of DTI is being expanded to evaluate a variety of spinal cord disorders both for prognostication and to guide therapy. The purpose of this article is to review the literature on spinal cord DTI in both animal models and humans in different neurosurgical conditions. DTI of the spinal cord shows promise in traumatic spinal cord injury, cervical spondylotic myelopathy, and intramedullary tumors. However, scanning protocols and image processing need to be refined and standardized.

Concept of robotic gamma knife microradiosurgery and results of its clinical application in benign skull base tumors

The availability of advanced computer-aided robotized devices for the Gamma Knife (i.e., an automatic positioning system and PerfeXion) resulted in significant changes in radiosurgical treatment strategy. The possibility of applying irradiation precisely and the significantly improved software for treatment planning led to the development of the original concept of robotic Gamma Knife microradiosurgery, which is comprised of the following: (1) precise irradiation of the lesion with regard to conformity and selectivity; (2) intentional avoidance of excessive irradiation of functionally important anatomical structures, particularly cranial nerves, located both within the target and in its vicinity; (3) delivery of sufficient radiation energy to the tumor with a goal of shrinking it while keeping the dose at the margins low enough to prevent complications. Realization of such treatment principles requires detailed evaluation of the microanatomy of the target area, which is achieved with an advanced neuroimaging protocol. From 2003, we applied the described microradiosurgical concept in our clinic for patients with benign skull base tumors. Overall, 75 % of neoplasms demonstrated shrinkage, and 47 % showed ≥50 % and more volume reduction. Treatment-related complications were encountered in only 6 % of patients and were mainly related to transient cranial nerve palsy. Just 2 % of neoplasms showed regrowth after irradiation. In conclusion, applying the microradiosurgical principles based on advanced neuroimaging and highly precise treatment planning is beneficial for patients, providing a high rate of tumor shrinkage and a low morbidity rate.

Usefulness of Leksell GammaPlan for preoperative planning of brain tumor resection: delineation of the cranial nerves and fusion of the neuroimaging data, including diffusion tensor imaging

Leksell GammaPlan (LGP) software was initially designed for Gamma Knife radiosurgery, but it can be successfully applied to planning of the open neurosurgical procedures as well. We present our initial experience of delineating the cranial nerves in the vicinity of skull base tumors, combined visualization of the implanted subdural electrodes and cortical anatomy to facilitate brain mapping, and fusion of structural magnetic resonance imaging and diffusion tensor imaging performed with the use of LGP before removal of intracranial neoplasms. Such preoperative information facilitated choosing the optimal approach and general surgical strategy, and corresponded well to the intraoperative findings. Therefore, LGP may be helpful for planning open neurosurgical procedures in cases of both extraaxial and intraaxial intracranial tumors.