Frameless stereotactic radiosurgery for the treatment of primary intracranial tumours in dogs.

Stereotactic radiosurgery (SRS) is a procedure that delivers a single large radiation dose to a well-defined target. Here, we describe a frameless SRS technique suitable for intracranial targets in canines. Medical records of dogs diagnosed with a primary intracranial tumour by imaging or histopathology that underwent SRS were retrospectively reviewed. Frameless SRS was used successfully to treat tumours in 51 dogs with a variety of head sizes and shapes. Tumours diagnosed included 38 meningiomas, 4 pituitary tumours, 4 trigeminal nerve tumours, 3 gliomas, 1 histiocytic sarcoma and 1 choroid plexus tumour. Median survival time was 399 days for all tumours and for dogs with meningiomas; cause-specific survival was 493 days for both cohorts. Acute grade III central nervous system toxicity (altered mentation) occurred in two dogs. Frameless SRS resulted in survival times comparable to conventional radiation therapy, but with fewer acute adverse effects and only a single anaesthetic episode required for therapy.

Isospin diffusion and the nuclear symmetry energy in heavy ion reactions.

Using symmetric 112Sn+112Sn, 124Sn+124Sn collisions as references, we probe isospin diffusion in peripheral asymmetric 112Sn+124Sn, 124Sn+112Sn systems at an incident energy of E/A=50 MeV. Isoscaling analyses imply that the quasiprojectile and quasitarget in these collisions do not achieve isospin equilibrium, permitting an assessment of isospin transport rates. We find that comparisons between isospin sensitive experimental and theoretical observables, using suitably chosen scaled ratios, permit investigation of the density dependence of the asymmetry term of the nuclear equation of state.

Initial clinical experience with frameless stereotactic radiosurgery: analysis of accuracy and feasibility.

PURPOSE: To report on preliminary clinical experience with a novel image-guided frameless stereotactic radiosurgery system. METHODS AND MATERIALS: Fifteen patients ranging in age from 14 to 81 received radiosurgery using a commercially available frameless stereotactic radiosurgery system. Pathologic diagnoses included metastases (12), recurrent primary intracranial sarcoma (1), recurrent central nervous system (CNS) lymphoma (1), and medulloblastoma with supratentorial seeding (1). Treatment accuracy was assessed from image localization of the stereotactic reference array and reproducibility of biteplate reseating. We chose 0.3 mm vector translation error and 0.3 degree rotation about each axis as the maximum tolerated misalignment before treating each arc. RESULTS: The biteplates were found on average to reseat with a reproducibility of 0.24 mm. The mean registration error from CT localization was found to be 0.5 mm, which predicts that the average error at isocenter was 0.82 mm. No patient treatment was delivered beyond the maximum tolerated misalignment. The radiosurgery treatment was delivered in approximately 25 min per patient. CONCLUSION: Our initial clinical experience with stereotactic radiotherapy using the infrared camera guidance system was promising, demonstrating clinical feasibility and accuracy comparable to many frame-based systems.

Isotropic beam bouquets for shaped beam linear accelerator radiosurgery.

In stereotactic radiosurgery and radiotherapy treatment planning, the steepest dose gradient is obtained by using beam arrangements with maximal beam separation. We propose a treatment plan optimization method that optimizes beam directions from the starting point of a set of isotropically convergent beams, as suggested by Webb. The optimization process then individually steers each beam to the best position, based on beam's-eye-view (BEV) critical structure overlaps with the target projection and the target's projected cross sectional area at each beam position. This final optimized beam arrangement maintains a large angular separation between adjacent beams while conformally avoiding critical structures. As shown by a radiosurgery plan, this optimization method improves the critical structure sparing properties of an unoptimized isotropic beam bouquet, while maintaining the same degree of dose conformity and dose gradient. This method provides a simple means of designing static beam radiosurgery plans with conformality indices that are within established guidelines for radiosurgery planning, and with dose gradients that approach those achieved in conventional radiosurgery planning.

Optically guided intensity modulated radiotherapy.

BACKGROUND AND PURPOSE: Previously, we reported on development of an optically guided system for 3D conformal intracranial radiotherapy using multiple noncoplanar fixed fields. In this paper we report on the extension of our system for stereotactic fractionated radiotherapy to include intensity modulated static ports. METHODS AND MATERIALS: A 3D treatment plan with maximum beam separation is developed in the stereotactic space established by an optically guided system. Gantry angles are chosen such that each beam has a unique entrance and exit pathway, avoids the critical structures, and has a minimal beam's eye view projection. Once, a satisfactory treatment plan is found using this geometric approach an inverse treatment plan is developed using the beam portals established previously. The purpose of adding inverse planing is two fold, on the one hand it allows further reduction of margins around the PTV, while on the other hand it affords the possibility of conformal avoidance of critical structures that are close to or abut the PTV. RESULTS: The use of the optically guided system in conjunction with intensity modulated noncoplanar radiotherapy treatment planning using fixed fields allows the generation of highly conformal treatment plans that exhibit smaller 90, 70, and 50% of prescription dose isodose volumes, improved PITV ratios, comparable or improved EUD, smaller NTD(mean) for the critical structures, and an inhomogeneity index that is within generally accepted limits. CONCLUSION: Because optically guided technology improves the accuracy of patient localization relative to the linac isocenter and allows real-time monitoring of patient position, the planning target volume needs to be corrected only for the limitations of image resolution. Intensity modulated static beam radiotherapy planning then provides the user the ability to further reduce margins on the PTV and to conform very closely to this smaller target volume, and enhances the normal tissue sparing, and high degree of conformality possible with 3D conformal radiotherapy. In addition, since optically guided technology affords improved patient localization and online monitoring of patient position during treatment delivery it allows for safe and efficient delivery of intensity modulated radiotherapy.

Analysis of risk factors associated with radiosurgery for vestibular schwannoma.

OBJECT: The aim of this study was to identify factors associated with delayed cranial neuropathy following radiosurgery for vestibular schwannoma (VS or acoustic neuroma) and to determine how such factors may be manipulated to minimize the incidence of radiosurgical complications while maintaining high rates of tumor control. METHODS: From July 1988 to June 1998, 149 cases of VS were treated using linear accelerator radiosurgery at the University of Florida. In each of these cases, the patient's tumor and brainstem were contoured in 1-mm slices on the original radiosurgical targeting images. Resulting tumor and brainstem volumes were coupled with the original radiosurgery plans to generate dose-volume histograms. Various tumor dimensions were also measured to estimate the length of cranial nerve that would be irradiated. Patient follow-up data, including evidence of cranial neuropathy and radiographic tumor control, were obtained from a prospectively maintained, computerized database. The authors performed statistical analyses to compare the incidence of posttreatment cranial neuropathies or tumor growth between patient strata defined by risk factors of interest. One hundred thirty-nine of the 149 patients were included in the analysis of complications. The median duration of clinical follow up for this group was 36 months (range 18-94 months). The tumor control analysis included 133 patients. The median duration of radiological follow up in this group was 34 months (range 6-94 months). The overall 2-year actuarial incidences of facial and trigeminal neuropathies were 11.8% and 9.5%, respectively. In 41 patients treated before 1994, the incidences of facial and trigeminal neuropathies were both 29%, but in the 108 patients treated since January 1994, these rates declined to 5% and 2%, respectively. An evaluation of multiple risk factor models showed that maximum radiation dose to the brainstem, treatment era (pre-1994 compared with 1994 or later), and prior surgical resection were all simultaneously informative predictors of cranial neuropathy risk. The radiation dose prescribed to the tumor margin could be substituted for the maximum dose to the brainstem with a small loss in predictive strength. The pons-petrous tumor diameter was an additional statistically significant simultaneous predictor of trigeminal neuropathy risk, whereas the distance from the brainstem to the end of the tumor in the petrous bone was an additional marginally significant simultaneous predictor of facial neuropathy risk. The overall radiological tumor control rate was 93% (59% tumors regressed, 34% remained stable, and 7.5% enlarged), and the 5-year actuarial tumor control rate was 87% (95% confidence interval [CI] 76-98%). Analysis revealed that a radiation dose cutpoint of 10 Gy compared with more than 10 Gy prescribed to the tumor margin yielded the greatest relative difference in tumor growth risk (relative risk 2.4, 95% CI 0.6-9.3), although this difference was not statistically significant (p = 0.207). CONCLUSIONS: Five points must be noted. 1) Radiosurgery is a safe, effective treatment for small VSs. 2) Reduction in the radiation dose has played the most important role in reducing the complications associated with VS radiosurgery. 3) The dose to the brainstem is a more informative predictor of postradiosurgical cranial neuropathy than the length of the nerve that is irradiated. 4) Prior resection increases the risk of late cranial neuropathies after radiosurgery. 5) A prescription dose of 12.5 Gy to the tumor margin resulted in the best combination of maximum tumor control and minimum complications in this series.

Isotopic scaling in nuclear reactions.

A three parameter scaling relationship between isotopic distributions for elements with Z< or =8 has been observed. This allows a simple description of the dependence of such distributions on the overall isospin of the system. This scaling law (termed isoscaling) applies for a variety of reaction mechanisms that are dominated by phase space, including evaporation, multifragmentation, and deeply inelastic scattering. The origins of this scaling behavior for the various reaction mechanisms are explained. For multifragmentation processes, the systematics is influenced by the density dependence of the asymmetry term of the equation of state.

Calibration of three-dimensional ultrasound images for image-guided radiation therapy.

A new technique of patient positioning for radiotherapy/radiosurgery of extracranial tumours using three-dimensional (3D) ultrasound images has been developed. The ultrasound probe position is tracked within the treatment room via infrared light emitting diodes (IRLEDs) attached to the probe. In order to retrieve the corresponding room position of the ultrasound image, we developed an initial ultrasound probe calibration technique for both 2D and 3D ultrasound systems. This technique is based on knowledge of points in both room and image coordinates. We first tested the performance of three algorithms in retrieving geometrical transformations using synthetic data with different noise levels. Closed form solution algorithms (singular value decomposition and Horn's quaternion algorithms) were shown to outperform the Hooke and Jeeves iterative algorithm in both speed and accuracy. Furthermore, these simulations show that for a random noise level of 2.5, 5, 7.5 and 10 mm, the number of points required for a transformation accuracy better than 1 mm is 25, 100, 200 and 500 points respectively. Finally, we verified the tracking accuracy of this system using a specially designed ultrasound phantom. Since ultrasound images have a high noise level, we designed an ultrasound phantom that provides a large number of points for the calibration. This tissue equivalent phantom is made of nylon wires, and its room position is optically tracked using IRLEDs. By obtaining multiple images through the nylon wires, the calibration technique uses an average of 300 points for 3D ultrasound volumes and 200 for 2D ultrasound images, and its stability is very good for both rotation (standard deviation: 0.4 degrees) and translation (standard deviation: 0.3 mm) transformations. After this initial calibration procedure, the position of any voxel in the ultrasound image volume can be determined in world space, thereby allowing real-time image guidance of therapeutic procedures. Finally, the overall tracking accuracy of our 3D ultrasound image-guided positioning system was measured to be on average 0.2 mm, 0.9 mm and 0.6 mm for the AP, lateral and axial directions respectively.

Emotional conversations in Parkinson's disease.

OBJECTIVE: To learn how PD influences verbal description of emotional events. BACKGROUND: Individuals with PD exhibit emotional processing deficits. Emotional experience likely involves several dimensions (e.g., valence, arousal, motor activation) subserved by a distributed modular network involving cortical, limbic, basal ganglia, diencephalic, and mesencephalic regions. Although the neurodegeneration in PD likely affects components in this network, little is known about how PD influences emotional processing. Because PD is associated with activation deficits, one could predict that the discourse of emotional experiences involving high activation would be reduced in patients with PD compared to control subjects. Alternatively, because patients with PD exhibit paradoxical sensitivity to externally evoked motor activation (kinesia paradoxica), it is possible that emotional stimuli may facilitate verbal emotional expression more so in patients with PD than in control subjects. METHODS: The authors measured verbal descriptions of personal emotional experiences in subjects with PD and normal controls. RESULTS: Compared with control subjects, individuals with PD showed a relative increase in the number of words spoken and in discourse duration when talking about emotional experiences that are usually associated with high levels of arousal and motor activation. Although the authors did not measure arousal or activation, prior research has shown that, when asked to recall an emotional experience, people will often re-experience the emotion previously experienced during that episode. CONCLUSIONS: Recalling emotional episodes induces verbal kinesia paradoxica in patients with PD. Although recall of these emotional episodes may have been associated with increased arousal and activation, the mechanism underlying emotional verbal kinesia paradoxica is unclear.

Stereotactic biopsy aided by a computer graphics workstation: experience with 200 consecutive cases.

BACKGROUND: The advent of modern computer technology has made it possible to examine not just the target point, but the entire trajectory in planning for stereotactic biopsies. METHODS: Two hundred consecutive biopsies were performed by one surgeon, utilizing a computer graphics workstation. The target point, entry point, and complete trajectory were carefully scrutinized and adjusted to minimize potential complications. RESULTS: Pathologically abnormal tissue was obtained in 197 cases (98.5%). There was no mortality in this series. Symptomatic hemorrhages occurred in 4 cases (2%). CONCLUSIONS: Computer graphics workstations facilitate safe and effective biopsies in virtually any brain area.

A neuropsychological outcome study of a child's left pericallosal arteriovenous malformation with occult fornix lesion.

Pericallosal arteriovenous malformations are rarely reported, particularly in children. Moreover, few arteriovenous malformation studies report thorough neuropsychological outcome data for assessing post-surgical functioning. This case report provides a longitudinal study of a boy who initially presented for neuropsychological testing at the age of 8 years and 1 month, following polyvinyl alcohol embolization, two craniotomies and resections and stereotactic radiosurgery for a pericallosal arteriovenous malformation involving nearly all of the corpus callosum. Follow-up magnetic resonance imaging also indicated absence of the left fornix. Functioning has been assessed over 7 years. Neuropsychological measures identified a consistent pattern of verbally mediated cognitive and memory deficits, with relatively spared visual perceptual and visual motor functioning. No evidence of a split-brain syndrome was found. The findings are consistent with insult to dominant hemisphere language and memory systems, provide an interesting example of neurodevelopmental compensation for significant early brain insult, and may provide insight into functions subserved by the fornix.

Radiosurgery using a stereotactic headframe system for irradiation of brain tumors in dogs.

Radiation therapy of brain tumors in dogs typically involves administration of multiple fractions over several weeks. Fractionation is used to minimize damage to normal tissue. Radiosurgery uses multiple non-coplanar stereotactically focused beams of radiation in a series of arcs to deliver a single dose to the target with extreme accuracy. The large number of beams facilitates a high degree of conformation between the treatment area and the target tumor and allows for a steep dose gradient; the use of nonintersecting arcs minimizes exposure of normal tissue. Computed tomography with a stereotactic localizer secured to the skull allows generation of a 3-dimensional image of the target and provides accurate spatial coordinates for computerized treatment planning and delivery. Three dogs were treated with radiosurgery, using 1,000 to 1,500 cGy. A linear accelerator mounted on a rotating gantry was used to generate and deliver the radiation. Two dogs with meningiomas survived 227 and 56 weeks after radiosurgery. A dog with an oligodendroglioma survived 66 weeks. No complications were observed following the use of this technique.

A geometrically based method for automated radiosurgery planning.

PURPOSE: A geometrically based method of multiple isocenter linear accelerator radiosurgery treatment planning optimization was developed, based on a target's solid shape. METHODS AND MATERIALS: Our method uses an edge detection process to determine the optimal sphere packing arrangement with which to cover the planning target. The sphere packing arrangement is converted into a radiosurgery treatment plan by substituting the isocenter locations and collimator sizes for the spheres. RESULTS: This method is demonstrated on a set of 5 irregularly shaped phantom targets, as well as a set of 10 clinical example cases ranging from simple to very complex in planning difficulty. Using a prototype implementation of the method and standard dosimetric radiosurgery treatment planning tools, feasible treatment plans were developed for each target. The treatment plans generated for the phantom targets showed excellent dose conformity and acceptable dose homogeneity within the target volume. The algorithm was able to generate a radiosurgery plan conforming to the Radiation Therapy Oncology Group (RTOG) guidelines on radiosurgery for every clinical and phantom target examined. CONCLUSIONS: This automated planning method can serve as a valuable tool to assist treatment planners in rapidly and consistently designing conformal multiple isocenter radiosurgery treatment plans.

A high-precision system for conformal intracranial radiotherapy.

PURPOSE: Currently, optimally precise delivery of intracranial radiotherapy is possible with stereotactic radiosurgery and fractionated stereotactic radiotherapy. We report on an optimally precise optically guided system for three-dimensional (3D) conformal radiotherapy using multiple noncoplanar fixed fields. METHODS AND MATERIALS: The optically guided system detects infrared light emitting diodes (IRLEDs) attached to a custom bite plate linked to the patient's maxillary dentition. The IRLEDs are monitored by a commercially available stereo camera system, which is interfaced to a personal computer. An IRLED reference is established with the patient at the selected stereotactic isocenter, and the computer reports the patient's current position based on the location of the IRLEDs relative to this reference position. Using this readout from the computer, the patient may be dialed directly to the desired position in stereotactic space. The patient is localized on the first day and a reference file is established for 5 different couch positions. The patient's image data are then imported into a commercial convolution-based 3D radiotherapy planning system. The previously established isocenter and couch positions are then used as a template upon which to design a conformal 3D plan with maximum beam separation. RESULTS: The use of the optically guided system in conjunction with noncoplanar radiotherapy treatment planning using fixed fields allows the generation of highly conformal treatment plans that exhibit a high degree of dose homogeneity and a steep dose gradient. To date, this approach has been used to treat 28 patients. CONCLUSION: Because IRLED technology improves the accuracy of patient localization relative to the linac isocenter and allows real-time monitoring of patient position, one can choose treatment-field margins that only account for beam penumbra and image resolution without adding margin to account for larger and poorly defined setup uncertainty. This approach enhances the normal tissue sparing, high degree of conformality, and homogeneity characteristics possible with 3D conformal radiotherapy.

Calculation of cranial nerve complication probability for acoustic neuroma radiosurgery.

PURPOSE: Estimations of complications from stereotactic radiosurgery usually rely simply on dose-volume or dose-diameter isoeffect curves. Due to the sparse clinical data available, these curves have typically not considered the target location in the brain, target histology, or treatment plan conformality as parameters in the calculation. In this study, a predictive model was generated to estimate the probability of cranial neuropathies as a result of acoustic schwannoma radiosurgery. METHODS AND MATERIALS: The dose-volume histogram reduction scheme was used to calculate the normal tissue complication probability (NTCP) from brainstem dose-volume histograms. The model's fitting parameters were optimized to provide the best fit to the observed complication data for acoustic neuroma patients treated with stereotactic radiosurgery at the University of Florida. The calculation was then applied to the remainder of the patients in the database. RESULTS: The best fit to our clinical data was obtained using n = 0.04, m = 0.15, and alpha/beta = 2.1 Gy(-1). Although the fitting parameter m is relatively consistent with ranges found in the literature, both the volume parameter, n, and alpha/beta are much smaller than the values quoted in the literature. The fit to our clinical data indicates that brainstem, or possibly a specific portion of the brainstem, is more radiosensitive than the parameters in the literature indicate, and that there is very little volume effect; in other words, irradiation of a small fraction of the brainstem yields NTCPs that are nearly as high as those calculated for entire volume irradiation. These new fitting parameters are specific to acoustic neuroma radiosurgery, and the small volume effect that we observe may be an artifact of the fixed relationship of acoustic tumors to specific regions of the brainstem. Applying the model to our patient database, we calculate an average NTCP of 7.2% for patients who had no cranial nerve complications, and the average NTCP for was 66% for patients who sustained a cranial neuropathy. For the entire patient population, the actual percentage of patients suffering either facial or trigeminal neuropathy was 14.7%, whereas the calculated average NTCP was 14.8%. DISCUSSION: NTCP calculations using brainstem dose-volume histograms can be used to estimate the rate of cranial neuropathies from acoustic neuroma radiosurgery. More clinical data and further study will lead to refinement of the model with time.

Stereotactic radiosurgery: techniques and clinical applications.

Radiation is a common treatment modality for cancer. Although commonly used, the treatment techniques of radiation delivery have changed substantially. One of the most important changes in implementation is the widespread application of stereotactic techniques and their acceptance into the mainstream of radiotherapeutic delivery. The distinguishing characteristics of stereotactic radiosurgery and its current and future application are important for all physicians to understand. This article discusses these treatment techniques and applications from the perspective of a surgical oncologist.

Linear accelerator radiosurgery in the management of brain tumours.

Radiosurgery is an increasingly popular method for treating a variety of intracranial tumours. A great deal of treatment data has been accumulated suggesting that radiosurgery may be the treatment of choice for small acoustic schwannomas. Moreover, radiosurgery promises excellent tumour control and minimal risk in the treatment of small meningiomas in risky surgical locations such as the cavernous sinus. Radiosurgery offers superior local control rates for many metastatic neoplasms and has promise as an adjuvant 'boost' technique in certain malignant gliomas. This article presents a brief description of the linear accelerator, LINAC, radiosurgical technique, followed by a review of the more common applications of stereotactic radiosurgery in the treatment of intracranial neoplastic disease.