Repositioning accuracy with the Laitinen frame for fractionated stereotactic radiation therapy in adult and pediatric brain tumors: preliminary report

Accuracy of 3D fluoroscopy in cranial stereotactic surgery: a comparative study in phantoms and patients

BACKGROUND

To assess the precision and accuracy of 3D fluoroscopy (XT) in phantoms and patients compared to computed tomography (CT) in localizing stereotactic probes.

METHODS

Approval was obtained from the institutional research ethics board. The prospective phantom study was compared to a retrospective patient cohort. Accuracy was assessed by the mean error and precision by the mean dispersion between XT and CT with a cubic or a skull phantom containing metallic spheres installed on plates or along trajectories. Significance was assessed by Friedman's and Levene's test. Secondary endpoints were Euclidean error, other influences e.g. installed frame and radiation exposure.

RESULTS

A total of 3,342 distances were assessed in 17 XT and 13 CT phantom scans. The cubic phantom showed mean distance errors of 0.33 mm (SD + -0.46 mm) for XT compared to 0.19 mm (SD + -0.83 mm) for CT scans (p = 0.0004) and a dispersion of 0.22 mm (XT) and 0.70 mm (CT). The dispersion was 0.36 mm with and 0.63 mm without a stereotactic frame (p < 0.0001). The mean Euclidean error was 0.72 mm (SD + -0.59 mm) in the skull phantom and 1.34 mm (SD + -0.82 mm) in the patient cohort. The effective dose was 0.65 mSv for the XT and 1.12 mSv for the CT.

CONCLUSIONS

The accuracy of XT imaging in phantoms revealed a slightly lower accuracy but higher precision than the CT. The overall accuracy of XT was higher than that of the stereotactic frame allowing stereotactic localization with about half of the effective dose of a CT-scan.

Six degrees of freedom CBCT-based positioning for intracranial targets treated with frameless stereotactic radiosurgery

Frameless radiosurgery is an attractive alternative to the framed procedure if it can be performed with comparable precision in a reasonable time frame. Here, we present a positioning approach for frameless radiosurgery based on in-room volumetric imaging coupled with an advanced six-degrees-of-freedom (6 DOF) image registration technique which avoids use of a bite block. Patient motion is restricted with a custom thermoplastic mask. Accurate positioning is achieved by registering a cone-beam CT to the planning CT scan and applying all translational and rotational shifts using a custom couch mount. System accuracy was initially verified on an anthropomorphic phantom. Isocenters of delineated targets in the phantom were computed and aligned by our system with an average accuracy of 0.2 mm, 0.3 mm, and 0.4 mm in the lateral, vertical, and longitudinal directions, respectively. The accuracy in the rotational directions was 0.1°, 0.2°, and 0.1° in the pitch, roll, and yaw, respectively. An additional test was performed using the phantom in which known shifts were introduced. Misalignments up to 10 mm and 3° in all directions/rotations were introduced in our phantom and recovered to an ideal alignment within 0.2 mm, 0.3 mm, and 0.4 mm in the lateral, vertical, and longitudinal directions, respectively, and within 0.3° in any rotational axis. These values are less than couch motion precision. Our first 28 patients with 38 targets treated over 63 fractions are analyzed in the patient positioning phase of the study. Mean error in the shifts predicted by the system were less than 0.5 mm in any translational direction and less than 0.3° in any rotation, as assessed by a confirmation CBCT scan. We conclude that accurate and efficient frameless radiosurgery positioning is achievable without the need for a bite block by using our 6DOF registration method. This system is inexpensive compared to a couch-based 6 DOF system, improves patient comfort compared to systems that utilize a bite block, and is ideal for the treatment of pediatric patients with or without general anesthesia, as well as of patients with dental issues. From this study, it is clear that only adjusting for 4 DOF may, in some cases, lead to significant compromise in PTV coverage. Since performing the additional match with 6 DOF in our registration system only adds a relatively short amount of time to the overall process, we advocate making the precise match in all cases.

Relocatable fixation systems in intracranial stereotactic radiotherapy. Accuracy of serial CT scans and patient acceptance in a randomized design

PURPOSE

The goal was to provide a quantitative evaluation of the accuracy of three different fixation systems for stereotactic radiotherapy and to evaluate patients' acceptance for all fixations.

METHODS

A total of 16 consecutive patients with brain tumours undergoing fractionated stereotactic radiotherapy (SCRT) were enrolled after informed consent (Clinical trials.gov: NCT00181350). Fixation systems evaluated were the BrainLAB® mask, with and without custom made bite-block (fixations S and A) and a homemade neck support with bite-block (fixation B) based on the BrainLAB® frame. The sequence of measurements was evaluated in a randomized manner with a cross-over design and patients' acceptance by a questionnaire.

RESULTS

The mean three-dimensional (3D) displacement and standard deviations were 1.16 ± 0.68 mm for fixation S, 1.92 ± 1.28 and 1.70 ± 0.83 mm for fixations A and B, respectively. There was a significant improvement of the overall alignment (3D vector) when using the standard fixation instead of fixation A or B in the craniocaudal direction (p = 0.037). Rotational deviations were significantly less for the standard fixation S in relation to fixations A (p = 0.005) and B (p = 0.03). EPI imaging with off-line correction further improved reproducibility. Five out of 8 patients preferred the neck support with the bite-block.

CONCLUSION

The mask fixation system in conjunction with a bite-block is the most accurate fixation for SCRT reducing craniocaudal and rotational movements. Patients favoured the more comfortable but less accurate neck support. To optimize the accuracy of SCRT, additional regular portal imaging is warranted.

Accuracy of relocation, evaluation of geometric uncertainties and clinical target volume (CTV) to planning target volume (PTV) margin in fractionated stereotactic radiotherapy for intracranial tumors using relocatable Gill-Thomas-Cosman (GTC) frame

The present study is aimed at determination of accuracy of relocation of Gill‐Thomas‐Cosman frame during fractionated stereotactic radiotherapy. The study aims to quantitatively determine the magnitudes of error in anteroposterior, mediolateral and craniocaudal directions, and determine the margin between clinical target volume to planning target volume based on systematic and random errors. Daily relocation error was measured using depth helmet and measuring probe. Based on the measurements, translational displacements in anteroposterior (z), mediolateral (x), and craniocaudal (y) directions were calculated. Based on the displacements in x, y and z directions, systematic and random error were calculated and three‐dimensional radial displacement vector was determined. Systematic and random errors were used to derive CTV to PTV margin. The errors were within ± 2 mm in 99.2% cases in anteroposterior direction (AP), in 99.6% cases in mediolateral direction (ML), and in 97.6% cases in craniocaudal direction (CC). In AP, ML and CC directions, systematic errors were 0.56, 0.38, 0.42 mm and random errors were 1.86, 1.36 and 0.73 mm, respectively. Mean radial displacement was 1.03 mm ± 0.34. CTV to PTV margins calculated by ICRU formula were 1.86, 1.45 and 0.93 mm; by Stroom's formula they were 2.42, 1.74 and 1.35 mm; by van Herk's formula they were 2.7, 1.93 and 1.56 mm (AP, ML and CC directions). Depth helmet with measuring probe provides a clinically viable way for assessing the relocation accuracy of GTC frame. The errors were within ± 2 mm in all directions. Systematic and random errors were more along the anteroposterior axes. According to the ICRU formula, a margin of 2 mm around the tumor seems to be adequate.

PACS number: 87.55.‐x

Reliability of the Bony Anatomy in Image-Guided Stereotactic Radiotherapy of Brain Metastases

PURPOSE

To evaluate whether the position of brain metastases remains stable between planning and treatment in cranial stereotactic radiotherapy (SRT).

METHODS AND MATERIALS

Eighteen patients with 20 brain metastases were treated with single-fraction (17 lesions) or hypofractionated (3 lesions) image-guided SRT. Median time interval between planning and treatment was 8 days. Before treatment a cone-beam CT (CBCT) and a conventional CT after application of i.v. contrast were acquired. Setup errors using automatic bone registration (CBCT) and manual soft-tissue registration of the brain metastases (conventional CT) were compared.

RESULTS

Tumor size was not significantly different between planning and treatment. The three-dimensional setup error (mean +/- SD) was 4.0 +/- 2.1 mm and 3.5 +/- 2.2 mm according to the bony anatomy and the lesion itself, respectively. A highly significant correlation between automatic bone match and soft-tissue registration was seen in all three directions (r >/= 0.88). The three-dimensional distance between the isocenter according to bone match and soft-tissue registration was 1.7 +/- 0.7 mm, maximum 2.8 mm. Treatment of intracranial pressure with steroids did not influence the position of the lesion relative to the bony anatomy.

CONCLUSION

With a time interval of approximately 1 week between planning and treatment, the bony anatomy of the skull proved to be an excellent surrogate for the target position in image-guided SRT.

A simple device for high-precision head image registration: Preliminary performance and accuracy tests

The purpose of this paper is to present a new device for multimodal head study registration and to examine its performance in preliminary tests. The device consists of a system of eight markers fixed to mobile carbon pipes and bars which can be easily mounted on the patient's head using the ear canals and the nasal bridge. Four graduated scales fixed to the rigid support allow examiners to find the same device position on the patient's head during different acquisitions. The markers can be filled with appropriate substances for visualisation in computed tomography (CT), magnetic resonance, single photon emission computer tomography (SPECT) and positron emission tomography images. The device's rigidity and its position reproducibility were measured in 15 repeated CT acquisitions of the Alderson Rando anthropomorphic phantom and in two SPECT studies of a patient. The proposed system displays good rigidity and reproducibility characteristics. A relocation accuracy of less than 1,5 mm was found in more than 90% of the results. The registration parameters obtained using such a device were compared to those obtained using fiducial markers fixed on phantom and patient heads, resulting in differences of less than 1 degree and 1 mm for rotation and translation parameters, respectively. Residual differences between fiducial marker coordinates in reference and in registered studies were less than 1 mm in more than 90% of the results, proving that the device performed as accurately as noninvasive stereotactic devices. Finally, an example of multimodal employment of the proposed device is reported.

Rotational and translational reproducibility of newly developed Leksell frame-based relocatable fixation system

PURPOSE

The aim of this study was to evaluate three-dimensional movement of the cranium in a relocatable frame using positions of anatomical landmarks obtained from repeated quality-assurance (QA) computed tomography (CT) studies.

MATERIALS AND METHODS

We analyzed 17 series of QA-CT data representing five patients who underwent stereotactic radiotherapy for treatment of acoustic neurinoma. Helical-CT scans with 1-mm collimation were obtained at the time of treatment planning and during the course of treatment. The right and left short processes of the incus and the top of the crista galli were used as the three anatomical reference points.

RESULTS

Fluctuations in distance among the reference points were all <1 mm. The translational displacements for these points were <2 mm, with standard deviations (SD) of <2 mm. A plane that included all three reference points was defined as the reference plane. To investigate the direction of cranial rotation for each QA-CT scan, unit normal vectors of the reference plane were obtained. Three-dimensional analyses indicated that cranial rotation was greatest along the X-axis, followed by the Y-axis, with the least rotation along the Z-axis.

CONCLUSION

The result suggested that movement of the craniocaudal axis in the sagittal plane was a major factor behind displacement of the cranium.

Fractionated stereotactic radiotherapy for pediatric patients with retinoblastoma

In this report, we discuss the application of a modified Gill‐Thomas‐Cosman (GTC) relocatable head frame to enable fractionated stereotactic radiotherapy (SRT) of infants under anesthesia. This system has been used to treat two infants, ages 12 and 18 months, for bilateral retinoblastoma on a Varian 6/100 linear accelerator. The GTC head frame was used to reproducibly position and treat the orbits of these children to between 2520 cGy and 3960 cGy in 180‐cGy fractions. A standard head and neck tray, with accompanying thermoplastic mask, was adapted to mount to the head frame to enable these treatments. We found the maximum average deviation in the repeat fixations, as compared with the initial fitting data, to be ±2mm. The overall average difference and standard deviation in measurement was 0.47±0.63mm for the first case and 0.19±0.94mm for the second case, with a combined average of 0.35±0.79mm overall from a total of 381 point measurements. The stereotactic treatment plan (Radionics®) incorporated a single isocenter for each orbit and 3 or 4 arcs per isocenter. An intercomparison has been made between this technique and a standard lateral field technique, designed using the stereotactic radiosurgery (SRS) planning system. Dose‐volume histograms and corresponding normal tissue complication probabilities (NTCP) based on pediatric bone growth inhibition have been calculated for each method for the orbital bone areas. We found that the NTCP is reduced from 95% or more in the standard treatment method to 16% or less with SRT. Use of the modified head frame provides excellent setup reproducibility, facilitates access to patients for anesthesia, and reduces the chances of a poor cosmetic result in these growing children.

PACS number: 87.53.Ly

Craniopharyngioma in childhood

In summary, much progress has been made in our understanding of childhood craniopharyngiomas. These histologically benign but "geographically malignant" tumors are challenging to treat and require experienced clinicians from multiple disciplines including neurosurgery, radiology, hematology/oncology, ophthalmology, endocrinology, and general pediatrics to address the multiple issues that arise with diagnosis, treatment, and long-term follow-up of affected children. The study and close observation of patients who have craniopharyngiomas may also be beneficial for our general understanding of pathophysiologic processes such as the observed "growth without growth hormone" phenomenon or the well-described and studied hypothalamic obesity phenotypes.

Radiation therapy in the management of pediatric craniopharyngiomas--a review

Craniopharyngiomas are benign suprasellar tumors that arise from epithelial remnants of the Rathke's pouch. The two standard treatment options are primary total resection or limited surgery followed by external beam radiation. The 10- and 20-year progression-free survival rates following limited surgery and radiation therapy are superior to those achieved by primary surgery alone. The side effect profiles for these two treatment approaches are different. Following total resection there is a very high incidence of panhypopituitarism requiring lifelong multiple hormone replacement therapy. The other side effects include potential damage to adjacent structures such as optic chiasm, vasculature and hypothalamus. Following limited surgery and radiation therapy the incidence of endocrine deficits is significantly lower compared to radical surgery, as is the risk of neurovascular and hypothalamic injury. Optic neuropathy and brain necrosis are rare in modern radiation therapy series. Second malignant neoplasms, although rare, can occur. In children with recurrent craniopharyngiomas following radical surgery, the recommended salvage treatment is radiation therapy, as further surgical attempts at salvage are associated with high relapse rates and increased morbidity and mortality. There have been significant technological advances in the field of radiation treatment planning and delivery that have great potential for reducing the incidence of long-term irradiation sequelae in the developing brain. The general availability of megavoltage linear accelerators and modern radiotherapy innovations such as three-dimensional conformal radiation treatment (3D CRT), stereotactic radiosurgery (SRS), stereotactic radiotherapy (SRT), and intensity modulated radiation therapy (IMRT) should further limit the rate of complications and improve cure rates in children with primary or recurrent craniopharyngioma.

Intracranial stereotactic positioning systems: Report of the American Association of Physicists in Medicine Radiation Therapy Committee Task Group No. 68

Intracranial stereotactic positioning systems (ISPSs) are used to position patients prior to precise radiation treatment of localized lesions of the brain. Often, the lesion is located in close proximity to critical anatomic features whose functions should be maintained. Many types of ISPSs have been described in the literature and are commercially available. These are briefly reviewed. ISPS systems provide two critical functions. The first is to establish a coordinate system upon which a guided therapy can be applied. The second is to provide a method to reapply the coordinate system to the patient such that the coordinates assigned to the patient's anatomy are identical from application to application. Without limiting this study to any particular approach to ISPSs, this report introduces nomenclature and suggests performance tests to quantify both the stability of the ISPS to map diagnostic data to a coordinate system, as well as the ISPS's ability to be realigned to the patient's anatomy. For users who desire to develop a new ISPS system, it may be necessary for the clinical team to establish the accuracy and precision of each of these functions. For commercially available systems that have demonstrated an acceptable level of accuracy and precision, the clinical team may need to demonstrate local ability to apply the system in a manner consistent with that employed during the published testing. The level of accuracy and precision required of an individual ISPS system is dependent upon the clinical protocol (e.g., fractionation, margin, pathology, etc.). Each clinical team should provide routine quality assurance procedures that are sufficient to support the assumptions of accuracy and precision used during the planning process. The testing of ISPS systems can be grouped into two broad categories, type testing, which occurs prior to general commercialization, and site testing, performed when a commercial system is installed at a clinic. Guidelines to help select the appropriate tests as well as recommendations to help establish the required frequency of testing are provided. Because of the broad scope of different systems, it is important that both the manufacturer and user rigorously critique the system and set QA tests appropriate to the particular device and its possible weaknesses. Major recommendations of the Task Group include: introduction of a new nomenclature for reporting repositioning accuracy; comprehensive analysis of patient characteristics that might adversely affect positioning accuracy; performance of testing immediately before each treatment to establish that there are no gross positioning errors; a general request to the Medical Physics community for improved QA tools; implementation of weekly portal imaging (perhaps cone beam CT in the future) as a method of tracking fractionated patients (as per TG 40); and periodic routine reviews of positioning accuracy.

Repositioning accuracy of fractionated stereotactic irradiation: assessment of isocentre alignment for different dental fixations by using sequential CT scanning

BACKGROUND AND PURPOSE

To quantify the accuracy and reproducibility of patient repositioning in fractionated stereotactic conformal radiotherapy (SCRT) using dental fixations in conjunction with a stereotactic head mask.

PATIENTS AND METHODS

One hundred and fourteen verification CT scans were performed on 57 patients in order to check set-up alignment. The first scan was done immediately after the first treatment. Twelve patients were checked for alignment accuracy with weekly CT scans over a period of 3-6 weeks, all others had 1-2 scans. Two different dental fixations were used in combination with a non-invasive mask system: an upper jaw support (35 patients) and a customised bite-block (17 patients). Five patients were treated with no additional fixation. Co-registration to the planning CT was used to assess alignment of the isocentre to the reference markers. Additionally, the intra-operator variability of image co-registration was assessed.

RESULTS

There was a significant improvement of the overall alignment in using the bite-block instead of the upper jaw support (P<0.001). The mean deviation was for the bite-block 2.2+/-1.1 mm (1 SD), for the upper jaw support 3.3+/-1.8 mm and 3.7+/-2.8 mm for the mask alone. Overall isocentre deviations independent of the method of fixation were 2.8 mm (1.7 mm, 1 SD). Displacements in CC direction were significantly less for the bite-block compared to the upper jaw support (P=0.03). The addition of an upper jaw support significantly reduced lateral rotations compared to the mask system alone (P=0.03). The intra-operator variability of image co-registration was 1.59+/-0.49 mm (1 SD).

CONCLUSION

The reproducibility of patient positioning using a re-locatable head mask system combined with a bite-block is within the reported range for similar devices and is preferable to a simple upper jaw support. In order to further reduce the margin for the planning target volume an intra-oral dental fixation is recommended.

Analysis of patient repositioning accuracy in precision radiation therapy using automated image fusion

This work describes a rapid and objective method of determining repositioning error during the course of precision radiation therapy using off‐line CT imaging and automated mutual‐information image fusion. The technique eliminates the variability associated with manual identification of anatomical landmarks by observers. A phantom study was conducted to quantify the accuracy of the image co‐registration‐based analysis itself. For CT voxel dimensions of 0.65×0.65×1.0mm3, the method is shown to detect translations with an accuracy of 0.5 mm in the anterior‐posterior and lateral dimensions and 0.8 mm in the superior‐inferior dimension. Phantom rotation in the coronal plane was detected to within 0.5° of expected values. The analysis has been applied to eight radiotherapy patients at two independent clinics, each immobilized by the same system for cranial stereotactic radiotherapy and CT‐imaged once per week over the five‐ to six‐week course of treatment. Among all patients, the ranges of translation in the anterior‐posterior, lateral, and superior‐inferior dimensions were −0.91mmto0.77mm,−0.66mm to1.02mm, and −2.24mm to3.47mm, respectively. Considering all patients and CT scans, the standard deviations of translation were 0.42 mm, 0.47 mm, and 1.36 mm in the anterior‐posterior, lateral, and superior‐inferior dimensions, respectively. The ranges of patient rotation about the superior‐inferior, left‐right, and anterior‐posterior axes were −2.84to2.62°,−1.74°to1.96°, and −1.78°to1.42°, respectively.

PACS numbers: 87.53.‐j, 87.53.Kn, 87.53.Ly, 87.53.Xd

Treatment accuracy of fractionated stereotactic radiotherapy

BACKGROUND AND PURPOSE

To assess the geometric accuracy of the delivery of fractionated stereotactic radiotherapy (FSRT) for brain tumours using the Gill-Thomas-Cosman (GTC) relocatable frame. Accuracy of treatment delivery was measured via portal images acquired with an amorphous silicon based electronic portal imager (EPI). Results were used to assess the existing verification process and to review the current margins used for the expansion of clinical target volume (CTV) to planning target volume (PTV).

PATIENTS AND METHODS

Patients were immobilized in a GTC frame. Target volume definition was performed on localization CT and MRI scans and a CTV to PTV margin of 5mm (based on initial experience) was introduced in 3D. A Brown-Roberts-Wells (BRW) fiducial system was used for stereotactic coordinate definition. The existing verification process consisted of an intercomparison of the coordinates of the isocentres and anatomy between the localization and verification CT scans. Treatment was delivered with 6 MV photons using four fixed non-coplanar conformal fields using a multi-leaf collimator. Portal imaging verification consisted of the acquisition of orthogonal images centred through the treatment isocentre. Digitally reconstructed radiographs (DRRs) created from the CT localization scans were used as reference images. Semi-automated matching software was used to quantify set up deviations (displacements and rotations) between reference and portal images.

RESULTS

One hundred and twenty six anterior and 123 lateral portal images were available for analysis for set up deviations. For displacements, the total errors in the cranial/caudal direction were shown to have the largest SD's of 1.2 mm, while systematic and random errors reached SD's of 1.0 and 0.7 mm, respectively, in the cranial/caudal direction. The corresponding data for rotational errors (the largest deviation was found in the sagittal plane) was 0.7 degrees SD (total error), 0.5 degrees (systematic) and 0.5 degrees (random). The total 3D displacement was 1.8 mm (mean), 0.8 mm (SD) with a range of 0.3-3.9 mm.

CONCLUSIONS

Portal imaging has shown that the existing verification and treatment delivery techniques currently in use result in highly reproducible setups. Random and systematic errors in the treatment planning and delivery chain will always occur, but monitoring and minimising them is an essential component of quality control. Portal imaging provides fast and accurate facility for monitoring patients on treatment and the results of this study have shown that a reduction in CTV to PTV margin from 5 to 4 mm (resulting in a considerable increase in the volume of normal tissue sparing) could be made.

Commissioning and clinical results utilizing the Gildenberg-Laitinen Adapter Device for X-ray in fractionated stereotactic radiotherapy

BACKGROUND

The Gildenberg-Laitinen Adapter Device for X-Ray (GLAD-X/LS) frame is a positioning device that allows the use of the same fiducial points as the Brown-Robert-Wells (BRW) system. Thus it permits treatment planning to be accomplished by the Radionics X-knife Radiosurgery Program. We investigated the commissioning and clinical benefits of the GLAD-X/LS for fractionated stereotactic radiotherapy (FSRT) in patients who were unable to tolerate the Gill-Thomas-Cosman (GTC) frame.

METHODS AND MATERIALS

Commissioning of the GLAD-X/LS system was done via use of a Rando Phantom. A target volume of 2 x 2 x 2 cm was drilled into the phantom head. An ion chamber and thermoluminescence dosimetric chips (TLDs) were implanted in the target. A simulated treatment course consisting of 5 stereotactic radiotherapy fractions (300 cGy, 30 mm collimator) was delivered to the phantom head. A total of 27 patients who could not tolerate the GTC frame were treated using the GLAD-X/LS system. A total of 35 isocenters were used; the median number of treatment fractions was eight. Reproducibility of the x, y, and z coordinates was examined and correlated to the same determined using orthogonal port films. Relocation accuracy and reproducibility were further assessed comparing the x, y, and z coordinates of the target center with multiplanar reconstructed coronal and sagittal images. Patient tolerance of the device was also evaluated daily throughout the treatment.

RESULTS

The measured TLD and ion chamber doses were within 3% of the prescribed dose at the isocenter. The same dose accuracy was also found at incremental distances of 5 mm, 10 mm, and 15 mm from the isocenter. All patients tolerated the treatment and the device well. Six patients experienced mild ear canal pain, and softer or smaller earpieces were substituted. The mean relocation accuracy was 1.5 mm +/- 0.8.

CONCLUSIONS

The GLAD-X/LS system has excellent accuracy and reproducibility with the mean relocation accuracy of 1.5 mm +/- 0.8. The device is well-tolerated by patients, with no significant complications. Larger scale studies are necessary before routine use can be recommended for the administration of FSRT.

Fractionated stereotactic radiotherapy: a short review

Currently, optimally precise delivery of intracranial radiotherapy is possible with stereotactic radiosurgery and fractionated stereotactic radiotherapy. We present in this article a review of the underlying basic physical and radiobiological principles of fractionated stereotactic radiotherapy and review the clinical experience for ateriovenus malformations, pituitary adenomas, mengiomas, vestibular schwanomas, low grade astrocytomas, malignant gliomas, and brain metastases.