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  • Author or Editor: Josef Novotny Jr x
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Mustafa Majali, Josef Novotny and Josef Novotny Jr.

Object. Extracranial doses received by patients undergoing Leksell gamma knife surgery (GKS) can be of clinical concern. Therefore, the ability to preestimate peripheral doses received outside the treatment field during the GKS would be beneficial and could be used for the optimization of treatment planning by providing a reference for practitioners to calculate the extracranial dose burden to the body before the start of treatment.

Methods. A dose of 40 Gy was delivered to the Rando phantom in a single fraction to a midline hypothetical target close to the center of the skull. Treatment planning was performed for multiple isocenters with a prescription to the 50% isodose of each collimator. Treatment plans were produced for 1, 5, 10, 15, and 20 shots, keeping the same dose and dose distribution at different target volumes. An automatic positioning system was used for positioning the phantom during the treatment. The doses to different organs were measured during GKS using a thermoluminescent dosimeter. In vivo measurements were also made in 200 patients who underwent GKS with the model C unit for different diagnoses at Na Homolce Hospital.

Conclusions. The peripheral dose depended on the collimator size with a logarithmic dependence on collimator size and a linear dependence on the number of shots. This model can be used for the estimation of peripheral doses with a total error less than 20%. This information can help clinicians with treatment planning optimization, especially in patients with long survival expectancy.

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Josef Novotný Jr., Aurelia Kollová and Roman Liščák

Object

This study was focused on the development of models with which to predict the occurrence of intracranial edema after Gamma Knife surgery (GKS) of meningiomas, based on clinical and imaging data collected in a large group of patients.

Methods

Data in 368 patients with 381 meningiomas treated using the Leksell Gamma Knife unit were analyzed. Follow up of more than 24 months was available in 331 patients (90%); this time period ranged from 24 to 120 months (median 51 months). The actuarial tumor control rate was 97.9% at 5 years. Perilesional edema after GKS was radiologically confirmed in 51 patients (15.4%) and 32 of them (9.7%) were symptomatic; symptoms were temporary in 23 (6.9%) and permanent in nine (2.7%). Ten different factors were proposed as potential predictors for the occurrence of the intracranial edema after GKS: patient's sex, patient's age, previous surgery, edema before GKS treatment, lobulated margin of meningioma, heterogeneous appearance of the tumor, tumor volume, tumor location, maximum dose to the tumor, and dose to the tumor margin. To identify factors having influence on edema occurrence, univariate and multivariate statistical analyses were performed.

There was a significant difference in the incidence of edema for different patient age groups and a significantly higher incidence of edema occurrence in patients in whom no surgical procedure was performed before GKS, those with edema present before GKS, those with a tumor volume larger than 10 cm3, those in whom the tumor was located in the anterior fossa, those in whom the maximum dose to the tumor was higher than 30 Gy, and for different tumor margin doses. A binary logistic regression multifactorial prediction model was used to identify the following significant factors to predict of edema occurrence after GKS: previous surgery, edema before the treatment, tumor volume, tumor location, and tumor margin dose.

Conclusions

Based on these models estimates of the occurrence of edema after the GKS can be made, and consequently treatment parameters can be adjusted to reduce the occurrence of edema. These results may provide grounds for additional patient care such as more frequent follow up or possibly administration of steroids.

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Gabriela Simonová, Josef Novotny Jr. and Roman Liscák

Object. The authors sought to evaluate local tumor control, complications, and progression-free survival in patients harboring low-grade gliomas who were treated with Leksell gamma knife surgery (GKS).

Methods. During a 6-year period 70 patients were treated for verified low-grade gliomas (Grade I or II) by GKS. Statistical analysis was based on 68 patients; two patients were lost to follow up. The median patient age was 17 years. The median target volume was 4200 mm. The median prescription dose was 25 Gy. The median number of fractions was five. Ninety-five percent of patients were treated in five daily fractions.

Partial or complete tumor regression was achieved in 83% of patients with a median time to response of 18 months. There was moderate acute or late toxicity in not more than 5% of patients. In this series the progression-free survival was 92% at 3 years and 88% at 5 years.

Conclusions. Relatively high local tumor control with minimal complications was achieved.

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Veronika Paštyková, Josef Novotný Jr., Tomáš Veselský, Dušan Urgošík, Roman Liščák and Josef Vymazal

OBJECTIVE

The aim of this study was to compare 3 different methods to assess the geometrical distortion of two 1.5-T and one 3-T magnetic resonance (MR) scanners and to evaluate co-registration accuracy. The overall uncertainty of each particular method was also evaluated.

METHODS

Three different MR phantoms were used: 2 commercial CIRS skull phantoms and PTGR known target phantom and 1 custom cylindrical Perspex phantom made in-house. All phantoms were fixed in the Leksell stereotactic frame and examined by a Siemens Somatom CT unit, two 1.5-T Siemens (Avanto and Symphony) MRI systems, and one 3-T Siemens (Skyra) MRI system. The images were evaluated using Leksell GammaPlan software, and geometrical deviation of the selected points from the reference values were determined. The deviations were further investigated for both definitions including fiducial-based and co-registration–based in the case of the CIRS phantom images. The same co-registration accuracy assessment was also performed for a clinical case. Patient stereotactic imaging was done on 3-T Skyra, 1.5-T Avanto, and CT scanners.

RESULTS

The accuracy of the CT scanner was determined as 0.10, 0.30, and 0.30 mm for X, Y, and Z coordinates, respectively. The total estimated uncertainty in distortion measurement in one coordinate was determined to be 0.32 mm and 0.14 mm, respectively, for methods using and not using CT as reference imaging. Slightly more significant distortions were observed when using the 3-T than either 1.5-T MR units. However, all scanners were comparable within the estimated measurement error. Observed deviation/distortion for individual X, Y, and Z stereotactic coordinates was typically within 0.50 mm for all 3 scanners and all 3 measurement methods employed. The total radial deviation/distortion was typically within 1.00 mm. Maximum total radial distortion was observed when the CIRS phantom was used; 1.08 ± 0.49 mm, 1.15 ± 0.48 mm, and 1.35 ± 0.49 mm for Symphony, Avanto, and Skyra, respectively. The co-registration process improved image stereotactic definition in a clinical case in which fiducial-based stereotactic definition was not accurate; this was demonstrated for 3-T stereotactic imaging in this study. The best results were shown for 3-T MR image co-registration with CT images improving image stereotactic definition by about 0.50 mm. The results obtained with patient data provided a similar trend of improvement in stereotactic definition by co-registration.

CONCLUSIONS

All 3 methods/phantoms used were evaluated as satisfactory for the image distortion measurement. The method using the PTGR phantom had the lowest uncertainty as no reference CT imaging was needed. Image co-registration can improve stereotactic image definition when fiducial-based definition is not accurate.

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Roman Liscák, Vilibald Vladyka, Gabriela Simonová, Josef Vymazal and Josef Novotny Jr.

Object. The authors conducted a study to record more detailed information about the natural course and factors predictive of outcome following gamma knife surgery (GKS) for cavernous hemangiomas.

Methods. One hundred twelve patients with brain cavernous hemangiomas underwent GKS between 1993 and 2000. The median prescription dose was 16 Gy. One hundred seven patients were followed for a median of 48 months (range 6–114 months). The rebleeding rate was 1.6%, which is not significantly different with that prior to radiosurgery (2%). An increase in volume was observed in 1.8% of cases and a decrease in 45%. Perilesional edema was detected in 27% of patients, which, together with the rebleeding, caused a transient morbidity rate of 20.5% and permanent morbidity rate of 4.5%. Before radiosurgery 39% of patients suffered from epilepsy and this improved in 45% of them. Two patients with brainstem cavernous hemangiomas died due to rebleeding. Rebleeding was more frequent in female middle-aged patients with a history of bleeding, a larger lesion volume, and a prescription dose below 13 Gy. Edema after GKS occurred more frequently in patients who had surgery, a larger lesion volume, and in those in whom the prescription dose was more than 13 Gy.

Conclusions. Gamma knife surgery of cavernous hemangiomas can produce an acceptable rate of morbidity, which can be reduced by using a lower margin dose. Lesion regression was observed in many patients. Radiosurgery seems to remain a suitable treatment modality in carefully selected patients.

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Daniela Tlachacova, Michal Schmitt, Josef Novotny Jr., Josef Novotny, Mustafa Majali and Roman Liscak

Object. The authors sought to compare the quality of treatment planning, radiation protection, and the time taken for treatment in the Leksell gamma knife model B with that using the model C Automatic Positioning System (APS).

Methods. Data were obtained in 463 patients treated with the B model and 518 patients treated with the C model. Data were analyzed in patients in whom the following diagnoses had been made: vestibular schwannoma, pituitary adenoma, meningioma, solitary metastasis, and other benign and malignant solitary tumors. Patients with arteriovenous malformations, ocular lesions, and functional diagnoses were excluded from this study.

Conclusions. With the C model there was a better conformity for most treated targets, such as vestibular schwannomas (p = 0.005) and meningiomas (p = 0.015). The level of radiation exposures to personnel was significantly decreased when using the model C (p < 0.001). There was no significant difference in radiation exposure of extracranial structures for the same number of shots in patients treated by both models. The mean time saved using the C model with the APS was 41 minutes per treatment. It would seem that the gamma knife model C permits better dose conformity, shorter treatment times, and less radiation exposure to personnel.

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Gabriela Simonova, Petra Kozubikova, Roman Liscak and Josef Novotny Jr.

OBJECTIVE

The purpose of this study was to evaluate long-term treatment results, radiation-related toxicity, and prognostic factors for the progression-free survival (PFS) of patients with pilocytic astrocytomas treated by means of stereotactic radiosurgery with a Leksell Gamma Knife.

METHODS

A total of 25 patients with pilocytic astrocytomas underwent Gamma Knife surgery during the period 1992–2002. The median target volume was 2700 mm3 (range 205–25,000 mm3). The 18 patients treated with 5 daily fractions received a median minimum target dose of 25 Gy. Doses for the 2 patients treated with 10 fractions over 5 days (2 fractions delivered on the same day at least 6 hours apart) were 23 and 28 Gy. For the 5 patients treated with a single fraction, the minimum target dose ranged from 13 to 20 Gy (median 16 Gy).

RESULTS

Complete regression occurred in 10 patients (40%) and partial regression in 10 patients (40%). The 10-year overall survival rate was 96% and the 10-year PFS rate was 80%. Target volume appeared to be a significant prognostic factor for PFS (p = 0.037). Temporary Grade 3 toxicity appeared in 2 patients (8%), and these patients were treated with corticosteroids for 2 months. Permanent Grade 4 toxicity appeared in 2 patients (8%) and was associated with neurocognitive dysfunction. In these 2 individuals, the neurocognitive dysfunction was also felt to be in part the result of the additional therapeutic interventions (4 in one case and 6 in the other) required to achieve durable control of their tumors.

CONCLUSIONS

Radiosurgery represents an alternative treatment modality for small residual or recurrent volumes of pilocytic astrocytomas and provides long-term local control. Target volume appears to be the most important factor affecting PFS.

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Josef Novotný Jr., Josef Novotný, Václav Spĕvác˘ek, Pavel Dvor˘ák, Tomás˘ Cechák, Roman Lis˘c˘ák, Gustav Broz˘ek, Jaroslav Tintĕra and Josef Vymazal

Object. The purpose of this study was to investigate the use of a polymer gel—based dosimeter for the evaluation of geometric and dosimetric inaccuracies during gamma knife radiosurgery and during the irradiation of an experimental animal.

Methods. A polymer gel dosimeter, based on acrylic monomers, was used for experiments conducted in this study. The accuracy of the dosimeter was evaluated on a Siemens EXPERT 1-tesla scanner in the transmitter/receiver head coil with the use of a multiecho sequence with 16 echoes, TE 22.5 to 360 msec, TR 2000 msec, slice thickness 2 mm, field of view 255 mm, and a pixel size of 0.5 × 0.5 mm2. Two experiments were conducted. First, the head phantom containing the polymer gel dosimeter was irradiated using 4-, 8-, 14-, and 18-mm isocenters. Second, a specially designed rat phantom was irradiated by four 4-mm isocenters. The dose profiles in the x, y, and z axes were calculated in the treatment planning system and measured with the polymer gel dosimeter and the results were compared.

There was good agreement between the measured and calculated dose profiles. The maximum deviation in the spatial position of the center of measured and calculated dose profiles was 0.5 mm in the head phantom and 1 mm in the rat phantom. The maximum deviation in the width of the selected reference isodose of measured profiles was 1.2 mm in the head phantom and 1.1 mm in the rat phantom.

Conclusions. The use of the polymer gel—based dosimeter for the verification of stereotactic procedures has advantages compared with other dosimetric systems. The dosimeter itself is tissue equivalent. Three-dimensional dose distributions can be measured and the dosimeter allows simulation of the therapeutic procedures.

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Josef Novotny Jr., Josef Vymazal, Josef Novotny, Daniela Tlachacova, Michal Schmitt, Pavel Chuda, Dusan Urgosik and Roman Liscak

Object. The authors sought to compare the accuracy of stereotactic target imaging using the Siemens 1T EXPERT and 1.5T SYMPHONY magnetic resonance (MR) units.

Methods. A water-filled cylindrical Perspex phantom with axial and coronal inserts containing grids of glass rods was fixed in the Leksell stereotactic frame and subjected to MR imaging in Siemens 1T EXPERT and Siemens 1.5T SYMPHONY units. Identical sequences were used for each unit. The images were transferred to the GammaPlan treatment planning system. Deviations between stereotactic coordinates based on MR images and estimated real geometrical positions given by the construction of the phantom insert were evaluated for each study. The deviations were further investigated as a function of the MR unit used, MR sequence, the image orientation, and the spatial position of measured points in the investigated volume.

Conclusions. Larger distortions were observed when using the SYMPHONY 1.5T unit than those with the EXPERT 1T unit. Typical average distortion in EXPERT 1T was not more than 0.6 mm and 0.9 mm for axial and coronal images, respectively. Typical mean distortion for SYMPHONY 1.5T was not more than 1 mm and 1.3 mm for axial and coronal images, respectively. The image sequence affected the distortions in both units. Coronal T2-weighted spin-echo images performed in subthalamic imaging produced the largest distortions of 2.6 mm and 3 mm in the EXPERT 1T and SYMPHONY 1.5T, respectively. Larger distortions were observed in coronal slices than in axial slices in both units, and this effect was more pronounced in SYMPHONY 1.5T. Noncentrally located slice positions in the investigated volume of the phantom were associated with larger distortions.

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Dusan Urgosik, Roman Liscak, Josef Novotny Jr., Josef Vymazal and Vilibald Vladyka

Object. The authors present the long-term follow-up results (minimum 5 years) of patients with essential trigeminal neuralgia (TN) who were treated with gamma knife surgery (GKS).

Methods. One hundred seven patients (61 females and 46 males) underwent GKS. The median follow up was time was 60 months (range 12–96 months). The target was the trigeminal root, and the maximum dose was 70 to 80 Gy. Repeated GKS was performed in 19 patients for recurrent pain, and the same dose was used.

Initial successful results were achieved in 96% of patients, with complete pain relief in 80.4%. Relief was achieved after a median latency of 3 months (range 1 day–13 months). Gamma knife surgery failed in 4% of patients. Pain recurred in 25% of patients after a median latent interval of 36 months (6–94 months). The initial success rate after a second GKS was 89% and 58% of patients were pain free. Pain relapse occurred in only one patient in this group. Hypesthesia was observed in 20% of patients after the first GKS and in 32% after the second GKS. The median interval to hypaesthesia was 35 months (range 3–94 months) after one treatment and 21 months (range 1–72 months) after a second treatment.

Conclusions. The initial success rate of pain relief was high and comparable to that reported in other studies. A higher than usual incidence of sensory impairment after GKS could be the long duration of follow-up study and due to the detailed neurological examination.