Stereotactic computer tomography with a modified Riechert-Mundinger device as the basis for integrated stereotactic neuroradiological investigations

Improved Accuracy for the Sturm-Pastyr Localizer in the Presence of Image Noise

Image guidance for frame-based stereotaxis is facilitated by incorporating three to four Sturm-Pastyr (SP) localizers into a stereotactic frame. Typically, each SP localizer enables the calculation of one set of \begin{document}\left ( x,y,z \right )\end{document} coordinates in the three-dimensional coordinate system of the stereotactic frame, given three sets of \begin{document}\left ( u, v \right )\end{document} coordinates created by the SP localizer in the two-dimensional coordinate system of a computed tomography (CT) image. Bouza and Brown propose formulas to calculate three sets of \begin{document}\left ( x,y,z \right )\end{document} coordinates for each SP localizer. Monte Carlo (MC) simulation compares the accuracy of the new formulation to the accuracy of the original SP formulation that calculates only one set of \begin{document}\left ( x,y,z \right )\end{document} coordinates for each SP localizer. Monte Carlo simulation reveals that the calculation of three sets of \begin{document}\left ( x,y,z \right )\end{document} coordinates instead of only one set improves the accuracy of image guidance.

The V-Localizer for Stereotactic Guidance

Image-guidance for frame-based stereotaxis is facilitated by incorporating three to four N-localizers or Sturm-Pastyr localizers into a stereotactic frame. An extant frame that incorporates only two N-localizers violates the fundamental principle of the N-localizer, which requires three non-colinear points to define a plane in three-dimensional space. Hence, this two N-localizer configuration is susceptible to error. The present article proposes the V-localizer that comprises multiple diagonal bars to provide four or more non-colinear points to minimize error.

Comparative Accuracies of the N-Localizer and Sturm-Pastyr Localizer in the Presence of Image Noise

The N-localizer and the Sturm-Pastyr localizer are two technologies that facilitate image-guided stereotactic surgery. Both localizers enable the geometric transformation of tomographic image data from the two-dimensional coordinate system of a medical image into the three-dimensional coordinate system of the stereotactic frame. Monte Carlo simulations reveal that the Sturm-Pastyr localizer is less accurate than the N-localizer in the presence of image noise.

Stereotactic interstitial brachytherapy for the treatment of oligodendroglial brain tumors

PURPOSE

We evaluated the treatment of oligodendroglial brain tumors with interstitial brachytherapy (IBT) using (125)iodine seeds ((125)I) and analyzed prognostic factors.

PATIENTS AND METHODS

Between January 1991 and December 2010, 63 patients (median age 43.3 years, range 20.8-63.4 years) suffering from oligodendroglial brain tumors were treated with (125)I IBT either as primary, adjuvantly after incomplete resection, or as salvage therapy after tumor recurrence. Possible prognostic factors influencing disease progression and survival were retrospectively investigated.

RESULTS

The actuarial 2-, 5-, and 10-year overall and progression-free survival rates after IBT for WHO II tumors were 96.9, 96.9, 89.8 % and 96.9, 93.8, 47.3 %; for WHO III tumors 90.3, 77, 54.9 % and 80.6, 58.4, 45.9 %, respectively. Magnetic resonance imaging demonstrated complete remission in 2 patients, partial remission in 13 patients, stable disease in 17 patients and tumor progression in 31 patients. Median time to progression for WHO II tumors was 87.6 months and for WHO III tumors 27.8 months. Neurological status improved in 10 patients and remained stable in 20 patients, while 9 patients deteriorated. There was no treatment-related mortality. Treatment-related morbidity was transient in 11 patients. WHO II, KPS ≥ 90 %, frontal location, and tumor surface dose > 50 Gy were associated with increased overall survival (p ≤ 0.05). Oligodendroglioma and frontal location were associated with a prolonged progression-free survival (p ≤ 0.05).

CONCLUSION

Our study indicates that IBT achieves local control rates comparable to surgery and radio-/chemotherapy treatment, is minimally invasive, and safe. Due to the low rate of side effects, IBT may represent an attractive option as part of a multimodal treatment schedule, being supplementary to microsurgery or as a salvage therapy after chemotherapy and conventional irradiation.

Stereotactic LINAC-Radiosurgery for Glomus Jugulare Tumors: A Long-Term Follow-Up of 27 Patients

BACKGROUND

The optimal treatment of glomus jugulare tumors (GJTs) remains controversial. Due to the critical location, microsurgery still provides high treatment-related morbidity and a decreased quality of life. Thus, we performed stereotactical radiosurgery (SRS) for the treatment of GJTs and evaluated the long-term outcome.

METHODS

Between 1991 and 2011, 32 patients with GJTs underwent SRS using a linear accelerator (LINAC) either as primary or salvage therapy. Twenty-seven patients (median age 59.9 years, range 28.7-79.9 years) with a follow-up greater than five years (median 11 years, range 5.3-22.1 years) were selected for retrospective analysis. The median therapeutic single dose applied to the tumor surface was 15 Gy (range 11-20 Gy) and the median tumor volume was 9.5 ml (range 2.8-51 ml).

RESULTS

Following LINAC-SRS, 10 of 27 patients showed a significant improvement of their previous neurological complaints, whereas 12 patients remained unchanged. Five patients died during follow-up due to old age or other, not treatment-related reasons. MR-imaging showed a partial remission in 12 and a stable disease in 15 patients. No tumor progression was observed. The actuarial overall survival rates after five, ten and 20 years were 100%, 95.2% and 79.4%, respectively.

CONCLUSIONS

Stereotactic LINAC-Radiosurgery can achieve an excellent long-term tumor control beside a low rate of morbidity in the treatment of GJTs. It should be considered as an alternative therapy regime to surgical resection or fractionated external beam radiation either as primary, adjuvant or salvage therapy.

Intracranial ganglioglioma WHO I: results in a series of eight patients treated with stereotactic interstitial brachytherapy

In this retrospective study we evaluated the efficacy of interstitial brachytherapy (IBT) using (125)Iodine seeds ((125)I) for intracranial ganglioglioma WHO I. Between October 1994 and March 2010, eight patients (m/f = 5/3, median age 30.4 years, age range 7-42.5 years) with intracranial ganglioglioma WHO I were treated with IBT using stereotactically implanted (125)I seeds. The median follow-up time was 41.5 months (range 16.7-140.1 months). Prior to interstitial brachytherapy one patient underwent microsurgical resection for three times; seven patients were treated with IBT primarily. In all patients we implanted the (125)I seeds stereotactically guided. The cumulative tumor surface dose ranged between 50 and 65 Gy (permanent implantation) and the median tumor volume was 5.6 ml (range 0.9-26 ml). After brachytherapy, follow-up MR imaging revealed complete remission in one patient, partial remission in three and stable disease in the remaining four patients. Five of eight patients presented with seizures were either seizure-free (1/5) or improved (4/5). Temporary treatment-related morbidity occurred in one patient only (headache, nausea/vomiting) and resolved completely under steroid medication after 4 weeks. No treatment-related mortality was observed. This study indicates that interstitial brachytherapy for the treatment of intracranial ganglioglioma WHO I is safe and provides a high rate of local tumor control. Due to the limited number of cases, it is not possible to conduct a rigorous statistical evaluation. Thus, larger numbers of patients are required.

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.

Long-Term Results of stereotactic Brachytherapy (Temporary 125Iodine Seeds) for the Treatment of Low-Grade Astrocytoma (Grade II)

Background

Treatment of low-grade astrocytoma (WHO grade II) (LGA II) remains a challenge. There is limited information regarding the long-term effects of stereotactic brachytherapy (SBT) (temporary ¹²⁵Iodine seeds) on patients with LGA II.

Objectives

The purpose of this study was to evaluate disease control and survival after stereotactic brachytherapy in patients with circumscribed and relatively small size tumors.

Materials and Methods

A retrospective review of 29 patients, treated between 1991 and 2011, was conducted to evaluate survival, complications, and local disease control after stereotactic brachytherapy. They belonged to a larger group of 48 cases with low-grade gliomas, treated with stereotactic brachytherapy. The demographic and clinical characteristics in patients including age, sex, and survival time were extracted from records.

Results

Thirteen patients were male and 16 were female, with the median age of 29 years (range, 2.5 – 64 years). The median follow-up was 95 (range, 6 – 240) months. Based on Pignatti classification, 10 patients were at low- and 19 patients at high-risk. The median overall as well as progression-free survivals for patients were 135 months (95% confidence interval: 76 – 194) and 96 months (95% confidence interval: 1 – 199), respectively. Five- and 10-year progression-free survivals were 41.4 % and 34.5 %, respectively, and the 5- and 10-year overall survivals were 65.5 % and 44.8%, respectively. Progression-free survival was not significantly higher in smaller size tumors (P = 0.224), nor for spherical versus non-spherical tumors (P = 0.307). There was no treatment-related morbidity after stereotactic brachytherapy, and no radiogenic complications occurred during the follow-up period. Mortality due to tumor progression occurred in 4 patients (14%), and 11 patients were alive at the last follow-up.

Conclusions

The stereotactic brachytherapy for patients with circumscribed and relatively small size tumors appears to be a safe, feasible, and minimally-invasive treatment.

Intracranial ependymoma: long-term results in a series of 21 patients treated with stereotactic (125)iodine brachytherapy

Background

We evaluated the long-term outcome in patients harboring intracranial ependymomas treated with interstitial brachytherapy (IBT).

Methods

Twenty-one patients (M/F = 9/12; median age: 29 years; range: 8–70 years), diagnosed with intracranial ependymoma (1 WHO I, 11 WHO II, 9 WHO III) were treated with IBT using stereotactically implanted ¹²⁵Iodine seeds between 1987 and 2010, either primarily, as adjuvant therapy following incomplete resection, or as salvage treatment upon tumor recurrence. Sixteen of 21 patients underwent microsurgical resection prior to IBT; in 5 patients, IBT was performed primarily after stereotactic biopsy for histological diagnosis. The cumulative tumor surface dose ranged from 50–65 Gy treating a median tumor volume of 3.6 ml (range, 0.3–11.6 ml). A median follow-up period of 105.3 months (range, 12.7–286.2 months) was evaluated.

Results

Actuarial 2-, 5- and 10-years overall- and disease-specific survival rates after IBT were each 90% and 100% at all times for ependymomas WHO I/II, for anaplastic ependymomas WHO III 100%, 100%, 70% and 100%, 100%, 86%, respectively. The neurological status of seven patients improved, while there was no change in 12 and deterioration in 2 patients, respectively. Follow-up MR images disclosed a complete tumor remission in 3, a partial remission in 12 and a stable disease in 6 patients. Treatment-associated morbidity only occurred in a single patient.

Conclusions

This study shows that stereotactic IBT for intracranial ependymomas is safe and can provide a high degree of local tumor control. Due to the low rate of side effects, IBT may evolve into an attractive alternative to microsurgery in ependymomas located in eloquent areas or as a salvage treatment.

Stereotactic iodine-125 brachytherapy for treatment of inoperable focal brainstem gliomas of WHO grades I and II: feasibility and long-term outcome

Microsurgical resection is the most frequently suggested treatment option for accessible focal brainstem gliomas (F-BSG) of World Health Organization (WHO) grades I and II. Because of their location in the highly eloquent brain, however, resection is associated with permanent postoperative morbidity, ranging from 12 to 33 %. Only a few reports have suggested stereotactic brachytherapy (SBT) with implantation of iodine-125 seeds as a local treatment alternative. Between 1993 and 2010, 47 patients were treated with SBT (iodine-125 seeds; cumulative surface dose 50-65 Gy) for inoperable F-BSG, WHO grades I and II, in one of the largest reported patient series. We evaluated procedure-related complications, clinical outcome, and progression-free and overall survival (PFS, OS). Median follow-up was 81.6 months. Procedure-related mortality was zero. Within 30 days of seed implantation six patients (12.8 %) had transient neurological deficits. Two patients (4.3 %) deteriorated permanently. Space-occupying cysts occurred in six patients (12.8 %) after a median of 28.5 months, and required surgical intervention. Nine patients (19.1 %) presented with tumor relapse after a median of 56.6 months (range 7.9-118.0 months). For the remaining 38 patients complete response was observed for 23.4 %, partial response for 29.8 %, and stable disease for 27.7 %. Actuarial PFS was 97.7 ± 2.2, 92.8 ± 4.0, 81.2 ± 6.5, and 62.0 ± 10.4 % after 1, 2, 5, and 10 years, respectively. Corresponding OS was 100 ± 0.0 % (1 and 2 years), 97.4 ± 2.6 % (5 years), and 87.6 ± 7.0 % (10 years). SBT is a comparatively safe, minimally invasive, and highly effective local treatment option for patients with inoperable F-BSG WHO grades I and II; it merits further evaluation in prospective randomized trials.

Papillary tumors of the pineal region: a novel therapeutic option-stereotactic 125iodine brachytherapy

We evaluated the efficacy of interstitial brachytherapy (IBT) using (125)Iodine ((125)I) seeds for treatment of papillary tumors of the pineal region. Between September 2003 and September 2010, four patients (M/F = 2/2; median age, 57.3 years; range 29.2-69.1 years) with papillary tumors of the pineal region underwent IBT using (125)I seeds. Before brachytherapy two patients underwent endoscopic ventriculo-cisternotomy, because of occlusive hydrocephalus, and subsequent microsurgical resection was performed on one; three patients were primarily treated with IBT. Median tumor volume was 3.3 ml (range 1.6-4 ml), the tumor surface dose ranged between 50 and 65 Gy. For three patients the seeds were implanted permanently whereas one patient received temporary implants (28 days). The median follow-up time was 53.6 months (range 13-103.4 months). After brachytherapy, follow-up MR images revealed complete remission in one patient, partial remission in two, and stable disease in the remaining patient. Neurological status improved in all patients (reduced headache and nausea/vomiting for four patients; improvement of oculomotor dysfunction for two of three patients partially and for one of three patients completely). Neither treatment-related morbidity nor mortality was observed. Our results are indicative of good local control of papillary tumors of the pineal region after IBT, without treatment-related morbidity.

μMLC-LINAC radiosurgery for intracranial meningiomas of complex shape

BACKGROUND

We present the long-term results of a consecutive series of patients with meningiomas treated by LINAC-radiosurgery using the micro-multi-leaf collimator technique (μMLC).

METHODS

Between May 2001 and July 2009, 78 patients (m: f = 024:54; median age, 56.8 years; range, 20.1-81 years) with 87 intracranial meningiomas (78 WHO I, seven WHO II, two WHO III) were treated with μMLC-LINAC radiosurgery at our institution, either as a primary or salvage treatment following one or more microsurgical procedures. Fifty-eight of 87 tumors (66.7%) were located in the skull base. The remaining 29 meningiomas (33.3%) were located in the convexity of the brain. The median tumor volume was 4.8 ml (range, 0.2-18.3 ml). The median tumor surface dose, maximal dose, and therapeutic isodose were 12 Gy, 16 Gy, and 75%, respectively.

RESULTS

For retrospective evaluation, we included 70 patients (78 tumors) with a minimum radiological follow-up of 24 months. After a median follow-up of 79.7 months (range, 24.2-109.1 months), 24 patients (34.3%) improved in their clinical status (paresis of N. abducens 18/48, facial paresis 4/8, and hemiparesis 2/9), 41 patients remained stable (58.6%), three patients had treatment-related temporary complaints (4.3%); two patients developed vertigo, and one had a left-sided hemihypesthesia. All complaints recovered completely after steroid medication within 2 weeks. Two patients (2.8%) developed permanent trigeminal neuralgia. Follow-up MR images showed a partial remission in 21 tumors (26.9%) and a stable tumor size in 55 cases (70.5%). Two patients with high-grade meningiomas showed a tumor progression (one WHO II and one WHO III meningioma). At the end of follow-up (July 2010), the actuarial 5- and 9-year progression-free survival after radiosurgery were 98 and 96%, respectively. There was no treatment-related mortality.

CONCLUSIONS

LINAC radiosurgery using a micro multi-leaf collimator for complex shaped intracranial meningiomas is effective yielding a high local tumor control, whereas the treatment-related morbidity remains low.

LINAC-radiosurgery for nonsecreting pituitary adenomas. Long-term results

BACKGROUND AND PURPOSE

Stereotactic linear accelerator-based radiosurgery (LINAC-RS) is increasingly used for microsurgically inaccessible or recurrent pituitary adenomas. This single-center study evaluates the long-term follow-up after LINAC-RS of nonsecreting pituitary adenomas (NSA).

PATIENTS AND METHODS

Between 1992 and August 2008, 65 patients with NSA were treated. Patient treatment and follow-up were conducted according to a prospective protocol. Indications for LINAC-RS were (1) tumor recurrence or (2) residual tumor. Three patients were treated primarily. For analysis of prognostic factors, patients were grouped according to epidemiological or treatment-associated characteristics.

RESULTS

A total of 61 patients with a follow-up ≥ 12 months (median 83 months, range 15-186 months, longest follow-up of published radiosurgery series) were evaluated with regard to their clinical, radiological, and endocrinological course. The median tumor volume was 3.5 ml (± 4.3 ml, range 0.3-17.3 ml) treated with a median surface and maximum dose of 13.0 Gy and 29.7 Gy, respectively. Local tumor control was achieved in 98%. One patient died of unrelated cause after 36 months and 1 patient developed a radiation-induced seizure disorder. Visual complications did not occur. In 37 of 41 patients (90.2%), pituitary function remained stable. Maximum dose to the pituitary ≤ 16 Gy and female gender were positive prognostic factors for the preservation of pituitary function.

CONCLUSION

LINAC-RS is a minimally invasive, safe, and effective treatment for recurrent NSA or microsurgically inaccessible residual tumor. LINAC-RS yielded a high rate of local long-term tumor control with a small number of radiation-induced side effects.

Stereotactic brachytherapy with iodine-125 seeds for the treatment of inoperable low-grade gliomas in children: long-term outcome

PURPOSE

Resection is generally considered the gold standard for treatment of low-grade (WHO grades I and II) gliomas (LGGs) in childhood. However, approximately 30% to 50% of these tumors are inoperable because of their localization in highly eloquent brain areas. A few reports have suggested stereotactic brachytherapy (SBT) with implantation of iodine-125 ((125)I) seeds as a safe and effective local treatment alternative. This single-center study provides a summary of the long-term outcome after SBT in one of the largest reported patient series.

PATIENTS AND METHODS

All pediatric patients treated with SBT ((125)I seeds; cumulative therapeutic dose 50-65 Gy within 9 months) by our group for LGG with follow-up of more than 6 months were included. Clinical and radiologic outcome, time to progression, and overall survival were evaluated. Prognostic factors (age, sex, Karnofsky performance score, tumor volume, and histology) for survival and disease progression were investigated.

RESULTS

In all, 147 of 160 pediatric patients treated with SBT (from 1982 through 2009) were analyzed in detail. Procedure-related mortality was zero, and the 30-day morbidity was transient and low (5.4%). Survival rates at 5 and 10 years were 93%, and 82%, respectively, with no significant difference between WHO grades I and II tumors (median follow-up, 67.1 ± 57.7 months). Twenty-one (14.8%) of 147 patients presented with tumor relapse. The remaining 126 patients revealed complete response in 24.6%, partial response in 31.0%, and stable disease in 29.6%. Neurologic status improved (57.8%) or remained stable (23.0%). None of the evaluated factors had significant impact on the study's end points except tumor volume more than 15 mL, which caused significantly higher rates of tumor recurrence (P < .05).

CONCLUSION

We demonstrate that SBT represents a safe, minimally invasive, and highly effective local treatment option for pediatric patients with inoperable LGG WHO grades I and II.

Stereotactic 125Iodine Brachytherapy for the Treatment of Singular Brain Metastases: Closing a Gap?

BACKGROUND:

Brain metastases represent the most common intracranial tumors and are associated with very poor prognosis.

OBJECTIVE:

To investigate the feasibility, survival, and cerebral disease control of patients with singular brain metastases treated with stereotactic 125iodine brachytherapy (SBT), to identify prognostic factors, and to compare results with other local treatment methods.

METHODS:

Complications, survival (overall and separated by recursive partitioning analysis [RPA] classes), and local and distant disease control were evaluated retrospectively in 90 patients. Prognostic factors were identified by forming subgroups of patients based on age, Karnofsky Performance Status, status of extracranial disease, interval since initial diagnosis, absence/presence of prior whole-brain radiation therapy, localization, morphology, and tumor volume.

RESULTS:

There was no treatment-related mortality, and morbidity was transient and low (3.3%). Median survival was 8.5 months overall and 18.1 months for RPA class 1 patients. After 1 year, the actuarial incidence of local and distant cerebral relapse was 5.4% and 46.4%, respectively. Karnofsky Performance Status ≥ 70 (P &lt; .002), stable systemic disease (P &lt; .02), RPA class 1 (P &lt; .02), and a prolonged (&gt; 12 month) interval between initial diagnosis and SBT (P &lt; .05) significantly improved survival. No significant influence of previous whole-brain radiation therapy on survival or cerebral disease relapse was found.

CONCLUSION:

SBT represents a safe, minimally invasive, and, compared with SRS and microsurgery, a similarly effective local treatment option in terms of survival and cerebral disease control. It allows histological (re-)evaluation and treatment within 1 stereotactic operation. Because it is less restricted by tumor localization or size, it greatly advances local treatment options, and on the basis of its favorable biological irradiation effect, SBT does not limit additional irradiation treatment in the event of disease relapse.

Stereotactic biopsy combined with stereotactic (125)iodine brachytherapy for diagnosis and treatment of locally recurrent single brain metastases

This paper reports on stereotactic biopsy combined with stereotactic (125)iodine brachytherapy (SBT) for locally recurrent, previously irradiated cerebral metastases, focusing on feasibility, complications, cerebral disease control, and survival. All patients with suspected locally recurrent metastases detected by MRI were selected for this combined procedure. After stereotactic biopsy, all patients with a verified vital tumor underwent SBT (50 Gy surface dose applied for 42 days) during the same surgical procedure. Histological results of biopsy, complications, treatment response, local and distant disease control, and survival were evaluated. Thirty patients underwent stereotactic biopsy, and 27 were treated with SBT for histologically proved tumor recurrence. There was no treatment-related mortality, and morbidity was transient and low (6.6%). Median survival was 14.8 months. After one year the actuarial incidence of local and distant relapse was 6.7 and 45.5%, respectively. There was no grade 3 or 4 CNS toxicity, even among the 18.5% of patients with tumors >30 mm. For these patients stereotactic biopsy seems to be a safe and valuable means of differentiating between radiation-induced tissue changes and tumor recurrence/progression. SBT is a safe, minimally invasive, and highly effective treatment option for cerebral disease control and survival. Furthermore, it can be performed during the same stereotactic operation.

Interstitial brachytherapy using stereotactic implanted (125)iodine seeds for recurrent medulloblastoma

AIMS

To evaluate the efficacy of interstitial brachytherapy using (125)iodine ((125)I) seeds for the treatment of recurrent multimodal treated medulloblastoma.

MATERIALS AND METHODS

Between September 1989 and August 2009, 12 patients (female:male=3:9, median age 19 years, range 7-55 years) with 23 recurrent medulloblastomas underwent interstitial brachytherapy using (125)I seeds. Before brachytherapy, all patients underwent microsurgical resection; six patients underwent a combined adjuvant treatment consisting of craniospinal irradiation and chemotherapy; three received craniospinal irradiation alone and two received chemotherapy alone. One patient was treated by surgery alone. The median tumour volume was 4.9ml (range 0.4-44.2ml), the median tumour surface dose 50Gy (range 32-50Gy) and the median implantation time 42 days (range 42-90 days). A median follow-up of 26 months was available (range 5-116 months).

RESULTS

After brachytherapy, nine of 23 tumours (39%) presented a complete remission, nine (39%) a partial remission and five (22%) stable disease on magnetic resonance images. The neurological status improved in six patients and remained unchanged in four. Two patients deteriorated: one developed spinal metastasis and another a treatment-related adverse radiation effect. Ten patients died due to disseminated disease despite local tumour control. The median survival after treatment was 15 months (range 5-68 months).

CONCLUSIONS

Our results show a good response of recurrent medulloblastoma after interstitial brachytherapy. High rates of tumour remission were yielded with low rates of treatment-related morbidity. Thus, (125)I seed brachytherapy should be considered as a treatment option for recurrent medulloblastoma.

Pineal parenchymal tumors. Management with interstitial iodine-125 radiosurgery

PURPOSE

To evaluate the efficacy of interstitial radiosurgery (IRS) for pineal parenchymal tumors (PPTs).

PATIENTS AND METHODS

18 consecutively admitted patients (twelve male and six female, age range 6-68 years, median age 34 years) with PPTs (eight pineocytomas, ten malignant PPTs) were treated at the authors' institution with IRS using stereotactically guided iodine-125 seed implantation ((125)I-IRS) as either primary or salvage therapy. The cumulative tumor surface dose ranged from 40 to 64 Gy. Adjuvant radiotherapy of the whole brain or the craniospine was done in patients with grade III and grade IV PPT. The median follow-up period was 57.4 months (range 6-134 months).

RESULTS

Overall actuarial 5- and 8-year survival rates after IRS were 100% and 86% for pineocytomas, and the overall actuarial 5-year survival rate was 78% for high-grade PPTs. Follow-up magnetic resonance imaging showed complete remission in 72% (13/18) and partial remission in 28% (5/18) of the cases. One patient developed an out-of-field relapse 4 years after partial remission of a pineocytoma, which had already been treated with IRS. There was no treatment-related mortality. Treatment-related morbidity occurred in two patients only.

CONCLUSION

This study indicates that stereotactic (125)I-IRS for the management of PPTs is quite efficient and safe. Due to the low rate of side effects, IRS may develop into an attractive alternative to microsurgery in de novo diagnosed pineocytomas. In malignant PPTs, IRS may be routinely applied in a multimodality treatment schedule supplementary to conventional irradiation.

COMBINED X-RAY AND MAGNETIC RESONANCE IMAGING FACILITY

OBJECTIVE

To assess the feasibility of a hybrid imaging setup combining x-ray and magnetic resonance imaging (MRI) in the setting of both stereotactic and functional neurosurgery.

METHODS

A combined x-ray and MRI scanning facility with a trolley system for a fast patient transfer between both modalities was installed in a neurosurgical setting. A registration algorithm for fusion of MRI scans and x-ray images was derived for augmentation of fluoroscopic x-ray projection images with MRI scan data, such as anatomic structures and planned probe trajectories. Phantom measurements were obtained between both modalities for estimation of registration accuracy. Practical application of our system in stereotactic and functional neurosurgery was tested in brachytherapy, deep brain stimulation, and motor cortex stimulation.

RESULTS

Phantom measurements yielded a mean spatial deviation of 0.7 +/- 0.3 mm with a maximum deviation of 1.1 mm for MRI scans versus x-rays. Augmentation of x-ray images with MRI scan data allowed intraoperative verification of the planned trajectory and target in three types of neurosurgical procedures: positioning iodine seeds in brachytherapy in one case with cerebellar metastasis, placement of electrodes for deep brain stimulation in two cases of advanced Parkinson's disease, and placement of an epidural grid for motor cortex stimulation in two cases of intractable pain.

CONCLUSION

Combined x-ray and MRI-guided stereotactic and functional neurosurgery is feasible. Augmentation of x-ray projection images with MRI scan data, such as planned probe trajectories and MRI scan segmented anatomic structures may be beneficial for probe guidance in stereotactic and functional neurosurgery.

Deep brain stimulation for Parkinson's disease

Indications for the treatment of Parkinson's disease (PD) with deep brain stimulation (DBS) are severe, therapy refractory tremor and complications of long-term levodopa uptake. Since its first application DBS has become a standard therapy for these patients. Theoretically, the ventrolateral part of the internal pallidum (GPI) or the subthalamic nucleus (STN) are suitable targets in order to treat all cardinal symptoms of patients in an advanced stage of PD stereotactically. Although clinical efficacy of both GPI or STN stimulation is obviously comparable, it has become widely accepted to prefer STN over GPI DBS. If PD-associated, medically intractable tremor is the most disabling symptom, stimulation of the ventrolateral motor thalamus can be an alternative. Anatomical targets for DBS are small and located in critical brain areas. Furthermore, this type of surgery is highly elective. As a consequence, high resolution multiplanar imaging and adequate treatment planning software are indispensable prerequisites for DBS surgery. Currently, commercially available impulse generators deliver a permanent high frequency periodic pulse train stimulation that interacts rather unspecifically with the firing pattern of both normal and pathological neurons. Prospectively, the development of more specific stimulation paradigms may help to improve the efficacy of this treatment modality.

Impact of target point deviations on control and complication probabilities in stereotactic radiosurgery of AVMs and metastases

OBJECTIVE

Determination of the impact of inaccuracies in the determination and setup of the target point in stereotactic radiosurgery (SRS) on the expectable complication and control probabilities.

METHODS

Two randomized samples of patients with arteriovenous malformation (AVM) (n=20) and with brain metastases (n=20) treated with SRS were formed, and the probability for complete obliteration (COP) or complete remission (CRP), the size of the 10 Gy-volume in the brain tissue (VOI10), and the probability for radiation necrosis (NTCP) were calculated. The dose-effect relations for COP and CRP were fitted to clinical data. Target point deviations were simulated through random vectors and the resulting probabilities and volumes were calculated and compared with the values of the treatment plan.

RESULTS

The decrease of the relative value of the control probabilities at 1mm target point deviation was up to 4% for AVMs and up to 10% for metastases. At 2 mm the median decrease was 5% for AVMs and 9% for metastases. The value for the target point deviation, at which COP and CRP decreased about 0.05 in 90% of the cases, was 1.3 mm. The increase of NTCP was maximally 0.0025 per mm target point deviation for AVMs and 0.0035/mm for metastases. The maximal increase of VOI10 was 0.7 cm(3)/mm target point deviation in both patient groups.

CONCLUSIONS

The upper limit for tolerable target point deviations is at 1.3mm. If this value cannot be achieved during the system test, a supplementary safety margin should be applied for the definition of the target volume. A better accuracy level is desirable, in order to ensure optimal chances for the success of the treatment. The target point precision is less important for the minimization of the probability of radiation necroses.

Deep-brain stimulation: long-term analysis of complications caused by hardware and surgery--experiences from a single centre

OBJECTIVE

To determine the surgery-related and hardware-related complications of deep-brain stimulation (DBS) at a single centre.

METHODS

262 consecutive patients (472 electrodes) operated for DBS in our department from February 1996 to March 2003 were retrospectively analysed to document acute adverse events (30 days postoperatively). The data of 180 of these patients were additionally revised to assess long-term complications (352 electrodes, mean follow-up 36.3 (SD 20.8) months).

RESULTS

The frequency of minor intraoperative complications was 4.2% (11/262 patients). Transient (0.2%) or permanent (0.4%) neurological deficits, and in one case asymptomatic intracranial haemorrhage (0.2%), were registered as acute severe adverse events caused by surgery. Among minor acute complications were subcutaneous bleeding along the extension wire (1.2%) and haematoma at the pulse generator implantation site (1.2%). Skin infection caused by the implanted material was registered in 15 of 262 patients (5.7%). The infection rate during the first observation period was 1.5% (4/262 patients) and the late infection rate was 6.1% (11/180 patients). Partial or complete removal of the stimulation system was necessitated in 12 of 262 (4.6%) patients because of skin infection. During the long-term observation period, hardware-related problems were registered in 25 of 180 (13.9%) patients.

CONCLUSIONS

Stereotactic implantation of electrodes for DBS, if performed with multiplanar three-dimensional imaging and advanced treatment planning software, is a safe procedure with no mortality and low morbidity. The main causes for the patients' prolonged hospital stay and repeated surgery were wound infections and hardware-related complications.

Accuracy and conformity of stereotactically guided interstitial brain tumour therapy using I-125 seeds

OBJECTIVE

To assess the accuracy of the stereotactic implantation procedure of catheters containing I-125 seeds in brain tumours and investigate the effect of catheter deviations on the dose distribution in patients.

METHODS

A randomised sample (n = 37) of all patients treated with I-125 seeds in our department between 6/1994 and 2/2002 was examined. Intraoperative X-ray images were used to measure deviations of implanted I-125 seed catheters from their planned positions and the influence on dose conformity, tumour surface dose and dose burden of surrounding healthy brain tissue was determined.

RESULTS

The mean spatial target point deviation was 2.0 mm (maximum 4.1 mm, SD 0.9 mm) and in 54.1% of the cases, reduction of the planned dose was greater than 5%. Target point deviations less than 1.5 mm have only minor influence on surface dose and conformity. Results indicated that in 10.8% of the cases the realized dose distribution showed a 'slight deviation', according to the guideline criteria for external radiosurgery of the Radiation Therapy Oncology Group. In 89.2% of the patients the applied dose conformed to the target volume.

CONCLUSIONS

Stereotactically guided interstitial irradiation with I-125 seeds can be used to treat brain tumours and metastases with high conformity comparable to radiosurgery. The observed deviations of the stereotactically implanted I-125 seed catheters from their planned target points were smaller when compared to frameless procedures. In order to maintain the required spatial accuracy of 1.5 mm in interstitial therapy using I-125 seeds, it appears necessary to optimise stereotactic instruments further.

Optimisation in stereotactic radiosurgery of AVMs: II. Comparison of arc and MMLC therapy

Two stereotactic surgery methods, arc and micro-multileave collimator (MMLC) therapy, were compared in the particular case of arteriovenous malformations (AVMs) treatment. Different methods of the treatment optimisation were used. The comparison covered a group of 22 patients suffering from peripheral and central AVMs of different sizes who underwent initially arc therapy. Several parameters were evaluated to compare the two methods: 2D and 3D isodose representations, dose-volume histograms (DVHs) and probability of success. The 3D isodoses were compared for the 22 patients showing a better conformity for the MMLC (three cases are presented). The DVHs of the AVM were also in favour of MMLC. In terms of probability of success, the results showed that are therapy was superior only in the case of small spherical lesions. MMLC therapy proved to be superior to arc therapy in all cases but central spherical small volume AVMs.

The influence of head frame distortions on stereotactic localization and targeting

A strong attachment of a stereotactic head frame to the patient's skull may cause distortions of the head frame. The aim of this work was to identify possible distortions of the head frame, to measure the degree of distortion occurring in clinical practice and to investigate its influence on stereotactic localization and targeting. A model to describe and quantify the distortion of the Riechert-Mundinger (RM) head frame was developed. Distortions were classified as (a) bending and (b) changes from the circular ring shape. Ring shape changes were derived from stereotactic CT scans and frame bending was determined from intraoperative stereotactic x-ray images of patients with implanted 125I-seeds acting as landmarks. From the examined patient data frame bending was determined to be 0.74 mm+/-0.32 mm and 1.30 mm in maximum. If a CT-localizer with a top ring is used, frame bending has no influence on stereotactic CT-localization. In stereotactic x-ray localization, frame bending leads to an overestimation of the z-coordinate by 0.37 mm+/-0.16 mm on average and by 0.65 mm in maximum. The accuracy of patient positioning in radiosurgery is not affected by frame bending. But in stereotactic surgery with an RM aiming bow trajectory displacements are expected. These displacements were estimated to be 0.36 mm+/-0.16 mm (max. 0.74 mm) at the target point and 0.65 mm+/-0.30 mm (max. 1.31 mm) at the entry point level. Changes from the circularring shape are small and do not compromise the accuracy of stereotactic targeting and localization. The accuracy of CT-localization was found to be close to the resolution limit due to voxel size. Our findings for frame bending of the RM frame could be validated by statistical analysis and by comparison with an independent patient examination. The results depend on the stereotactic system and details of the localizers and instruments and also reflect our clinical practice. Therefore, a generalization is not possible. Preliminary experience with a new MR-compatible RM head frame made of ceramics shows no frame distortions as with the conventional frame made of an Al-Cu-Mg alloy.

MR-guided stereotactic neurosurgery—comparison of fiducial-based and anatomical landmark transformation approaches

For application in magnetic resonance (MR) guided stereotactic neurosurgery, two methods for transformation of MR-image coordinates in stereotactic, frame-based coordinates exist: the direct stereotactic fiducial-based transformation method and the indirect anatomical landmark method. In contrast to direct stereotactic MR transformation, indirect transformation is based on anatomical landmark coregistration of stereotactic computerized tomography and non-stereotactic MR images. In a patient study, both transformation methods have been investigated with visual inspection and mutual information analysis. Comparison was done for our standard imaging protocol, including t2-weighted spin-echo as well as contrast enhanced t1-weighted gradient-echo imaging. For t2-weighted spin-echo imaging, both methods showed almost similar and satisfying performance with a small, but significant advantage for fiducial-based transformation. In contrast, for t1-weighted gradient-echo imaging with more geometric distortions due to field inhomogenities and gradient nonlinearity than t2-weighted spin-echo imaging, mainly caused by a reduced bandwidth per pixel, anatomical landmark transformation delivered markedly better results. Here, fiducial-based transformation yielded results which are intolerable for stereotactic neurosurgery. Mean Euclidian distances between both transformation methods were 0.96 mm for t2-weighted spin-echo and 1.67 mm for t1-weighted gradient-echo imaging. Maximum deviations were 1.72 mm and 3.06 mm, respectively.

Optimized distortion correction of epi-based statistical parametrical maps for stereotactic neurosurgery

A new approach is presented for unwarping geometrical distortions in echo planar imaging (EPI)-based statistical parametrical maps (SPM). With the developed method, a substantial reduction of geometrical distortions in the order of 5-15 mm down to a residue of approximately 1-2 mm was possible, thus allowing reliable activation localization and, hence, interpretation after fusion with undistorted conventional anatomic images. The unwarping procedure is an optimized combination of two distortion correction methods, the "inhomogeneity mapping" and the coregistration approach. Local and global distortions, the first one object-dependent, the second one caused by imperfect gradient waveforms, are reduced. With several examples of patients and volunteers, the applicability for stereotactic neurosurgery is demonstrated.

Stereotactic linear accelerater-based radiosurgery for the treatment of patients with glomus jugulare tumors

BACKGROUND

The optimal treatment for patients with glomus jugulare tumor (GJT) of the skull base remains controversial. Surgical excision is associated with a high incidence of cranial nerve injury, decreased quality of life, and high mortality. Fractionated radiotherapy is used to control the majority of these tumors, but disadvantages are a prolonged therapy interval and exposition of adjacent brain tissue to irradiation. The authors present the results of a study on 12 of 14 consecutively admitted patients who were treated using linear accelerator-based radiosurgery (LINAC-RS), an innovative method for the treatment of GJT.

METHODS

From May 1991 to March 2001, 14 patients with GJT were treated with stereotactic LINAC-RS for continued growth of tumor or of remaining tumor after surgery. Twelve patients (9 women and 3 men; age range, 28-71 years; median age, 59 years) with a median follow-up of 4 years (range, 0.8-9,0 years), were selected for retrospective analysis. A median single dose of 15 grays (Gy; range, 11-20 Gy) was applied to the surface of the tumor.

RESULTS

After undergoing LINAC-RS, 8 of 12 patients (67%) reported partial or complete subjective improvement, whereas complaints remained unchanged in 4 patients (33%). Neurologic status improved in 3 patients (25%) and remained unchanged in 8 patients (67%). Magnetic resonance images showed tumor shrinkage in 8 patients (67%) and no further progression in 4 patients (33%).

CONCLUSIONS

LINAC-RS is an effective and safe therapy for patients with GJT and may be used as an alternative to surgical resection. Compared with fractionated radiotherapy, LINAC-RS has some advantages. However, to clarify the question of long-term tumor control, longer observation times are required.

Stereotactic imaging for radiotherapy: accuracy of CT, MRI, PET and SPECT

CT, MRI, PET and SPECT provide complementary information for treatment planning in stereotactic radiotherapy. Stereotactic correlation of these images requires commissioning tests to confirm the localization accuracy of each modality. A phantom was developed to measure the accuracy of stereotactic localization for CT, MRI, PET and SPECT in the head and neck region. To this end. the stereotactically measured coordinates of structures within the phantom were compared with their mechanically defined coordinates. For MRI, PET and SPECT, measurements were performed using two different devices. For MRI, T1- and T2-weighted imaging sequences were applied. For each measurement, the mean radial deviation in space between the stereotactically measured and mechanically defined position of target points was determined. For CT, the mean radial deviation was 0.4 +/- 0.2 mm. For MRI, the mean deviations ranged between 0.7 +/- 0.2 mm and 1.4 +/- 0.5 mm, depending on the MRI device and the imaging sequence. For PET, mean deviations of 1.1 +/- 0.5 mm and 2.4 +/- 0.3 mm were obtained. The mean deviations for SPECT were 1.6 +/- 0.5 mm and 2.0 +/- 0.6 mm. The phantom is well suited to determine the accuracy of stereotactic localization with CT, MRI, PET and SPECT in the head and neck region. The obtained accuracy is well below the physical resolution for CT, PET and SPECT, and of comparable magnitude for MRI. Since the localization accuracy may be device dependent, results obtained at one device cannot be generalized to others.

Dose-response curves for late functional changes in the normal rat brain after single carbon-on doses evaluated by magnetic resonance imaging: influence of follow-up time and calculation of relative biological effectiveness

This study investigated late effects in the brain after irradiation with carbon ions using a rat model. Thirty-six animals were irradiated stereotactically at the right frontal lobe using an extended Bragg peak with maximum doses between 15.2 and 29.2 Gy. Dose-response curves for late changes in the normal brain were measured using T1- and T2-weighted magnetic resonance imaging (MRI). Tolerance doses were calculated at several effect probability levels and times after irradiation. The MRI changes were progressive in time up to 17 months and remained stationary after that time. At 20 months the tolerance doses at the 50% effect probability level were 20.3 +/- 2.0 Gy and 22.6 +/- 2.0 Gy for changes in T1- and T2-weighted MRI, respectively. The relative biological effectiveness (RBE) was calculated on the basis of a previous animal study with photons. Using tolerance doses at the 50% effect probability level, RBE values of 1.95 +/- 0.20 and 1.88 +/- 0.18 were obtained for T1- and T2-weighted MRI. A comparison with data in the literature for the spinal cord yielded good agreement, indicating that the RBE values for single-dose irradiations of the brain and the spinal cord are the same within the experimental uncertainty.

Dose-response curves and tolerance doses for late functional changes in the normal rat brain after stereotactic radiosurgery evaluated by magnetic resonance imaging: influence of end points and follow-up time

Late reaction of normal tissue is still a limiting factor in radiotherapy and radiosurgery of patients with brain tumors. Few quantitative data in terms of dose-response curves are available. In the present study, 99 animals were irradiated stereotactically at the right frontal lobe using a linear accelerator and single doses between 26 and 50 Gy. The diameter of the spherical dose distribution was 4.7 mm (80% isodose). Dose-response curves for late changes in the normal brain at 20 months were measured using T1- and T2-weighted magnetic resonance imaging (MRI). The dependence of the dose-response curves on the follow-up time and the definition of the biological end point were determined. Tolerance doses were calculated at several effect probability levels and times after irradiation. The MRI changes were found to be dependent on dose and progressive in time. At 20 months, the tolerance doses at a 50% effect probability level were 39.6 +/- 1.0 Gy and 42.4 +/- 1.4 Gy for changes in T1- and T2-weighted images, respectively. These dose-response curves can be used for further quantitative investigations on the influence of various treatment parameters, such as the application of charged particles, radiopharmaceuticals or the variation of tissue oxygenation.

Bilateral high-frequency stimulation in the subthalamic nucleus for the treatment of Parkinson disease: correlation of therapeutic effect with anatomical electrode position

OBJECT

The goal of this study was to relate the degree of clinical improvement and that of energy consumption to the anatomical position of electrode poles used for long-term stimulation.

METHODS

The authors conducted a retrospective analysis of 15 consecutive patients in whom targeting of the subthalamic nucleus (STN) had been performed using ventriculography, three-dimensional (3D) magnetic resonance (MR) imaging, and 3D computerized tomography, together with macrostimulation and teleradiographic control of the electrode position. In these patients the follow-up period ranged from 6 to 12 months. Postoperative improvement in contralateral motor symptoms, which was assessed by assigning a lateralized motor subscore of the Unified Parkinson's Disease Rating Scale (UPDRS), and stimulus intensity required for optimal treatment results were correlated with the intracerebral position of the active electrode pole. Bilateral high-frequency stimulation of the STN improved the UPDRS motor score during the medication-off period by an average of 60.5% compared with that at baseline. Repeated transfer of stereotactic coordinates from postoperative teleradiography to treatment-planning MR images documented the proper localization of the most distal electrode pole (pole 0) in the targeted STN. Nevertheless, in most cases the best clinical improvement was achieved using electrode poles that were located several millimeters above the electrode tip. If the relative improvement in motor symptoms was correlated with the required electrical energy for chronic stimulation, the best coefficient was observed for active electrode poles projecting onto white matter dorsal to the STN.

CONCLUSIONS

This observation makes blocking or activation of large fiber connections arising in the STN or running nearby more likely than electrical interference with cell bodies inside the STN. Anatomical correlates may be the pallidothalamic bundle (including Field H of Forel and the thalamic fascicle), the pallidosubthalamic tract, and/or the zona incerta.

Quantification of microglial late reaction to stereotactic irradiation of the rat brain using computer-aided image analysis

The role of microglial cells in the late delayed reaction following radiotherapy of brain tumors has not been elucidated. To investigate the late delayed response of microglial cells to radiation, we stereotactically irradiated spherical treatment volumes in the right frontal lobe of rat brains. Doses of 20, 30, 40, and 50 Gy were used in combination with two different collimators. The response of microglial cells at 10 and 19 months after irradiation was determined with Anti-CD 11 b/c (Ox 42) as an immunohistochemical marker. For evaluation of immunostaining, we developed a method using computer-aided image analysis in which the ratio of the area of stained cells to that of nonstained brain tissue is calculated. In addition, quantification of Ox-42+ cells per microscopic field was performed. Animals treated with 30 Gy or more had significantly increased total areas of staining at both time points studied. In contrast, the number of stained cells at 10 months increased significantly only in animals treated with 30 or 40 Gy. Likewise, at 19 months, this number increased significantly only in animals treated with 40 Gy or more. These results indicate that computer-aided determination of the area of stained cells is more sensitive than the counting of stained cells. We have demonstrated that microglial cells respond to stereotactic irradiation in a dose-dependent fashion. The image analysis we employed for this purpose is a systematic method to evaluate immunohistochemical staining.

Delayed vascular injury after single high-dose irradiation in the rat brain: histologic immunohistochemical, and angiographic studies

PURPOSE

To investigate structural and functional changes in rats after focal brain irradiation by using histologic, immunohistochemical, and angiographic methods.

MATERIALS AND METHODS

Sixty rats were irradiated stereotactically with photons from a 15-MeV linear accelerator. Two collimators and single doses ranging from 20 to 100 Gy were used to treat stereotactically defined areas of 3.7- and 4.7-mm cross section (80% isodose) in the right frontal lobe. The dose-response relationship for the end-point necrosis at 19 months revealed a mean tolerance dose (D50) of 34.2 Gy (standard errors: +4.1, -3.7 Gy). Histologic, immunohistochemical, and angiographic examinations were performed to evaluate delayed radiation effects.

RESULTS

All animals irradiated with 100 Gy developed radiation necrosis after 9 months. Microangiography and immunohistochemical fluorescence staining of the endothelial cells revealed dose-dependent vascular dilatation and rarefaction. Animals irradiated with 20-50 Gy showed no morphologic changes after 9 months. With irradiation of 30-50 Gy, histologic vascular changes that increased with dose were found after 19 months. At that time, no changes were detected after irradiation with 20 Gy with both field sizes and after irradiation with 30 Gy and the 2-mm collimator. Radiation-induced functional disturbances of the brain vasculature could be demonstrated by extravasation of contrast medium by using a microangiographic technique.

CONCLUSION

The observed effect had a definite dependence on dose, volume, and time after treatment.

Computer-guided laser probe for ablation of brain tumours with ultrashort laser pulses

A computer-guided laser probe has been developed for the application of ultrashort-pulsed lasers in neurosurgery. It is part of a novel operation concept for the treatment of deep-seated brain tumours. The system combines the positioning accuracy of stereotactic or neuronavigated instruments with the precise and therefore gentle characteristics of surgical lasers. The probe has an outer diameter of 5.5 mm and is directly inserted into the target volume. By a synchronized movement of three coaxial tubes, which guide the embedded optics, the laser radiation is focused at any time onto the current tissue surface. Since every single laser pulse has only a small effective volume of about 8 x 10(5) microm3, the application of a large number of succeeding pulses can be adapted to required geometries. Tissue fragments are removed from the growing operation cavity by continuous irrigation and suction through the laser probe. Blood vessels are detected by a confocal laser-scanning microscope, which is integrated into the probe, and can be closed by an additional coagulating laser. In this paper, the design and technical properties of the laser probe as well as its use in ablation and coagulation experiments are presented. A description of the overall operation system is given.

Linear accelerator radiosurgery for recurrent malignant tumors of the skull base

The efficacy of linear accelerator-based radiosurgery for patients who have preirradiated recurrent nasopharyngeal carcinomas and unresectable recurrent sarcomas invading the base of skull was assessed. Thirteen patients were treated: 8 patients had carcinomas arising from the nasopharynx (lymphoepithelioma, 4; squamous cell carcinoma, 2; adenoid-cystic, 2); 5 patients had sarcomas (rhabdomyosarcoma, 1; chordoma, 1; chondrosarcoma, 1; hemangiopericytoma, 2). All patients had had repeated tumor resections or irradiation, hindering any further conventional fractionated radiotherapy or surgery. Convergent-beam irradiation was performed with a modified linear accelerator (8-MeV photons). Because of irregular tumor configuration, multiple (up to seven) isocenters had to be used in 10 of 13 patients to match the target volume with the reference isodose (60%-80%). Each isocenter was irradiated with 6 to 10 arcs. The median planning target volume was 33 mL (4-128 mL) and the median dose was 15 Gy (9-24 Gy). Median survival time was 9 months in 8 patients who had recurrent nasopharyngeal carcinomas. Three patients who had complete or partial tumor remission survived 1.5 to 3.5 years. All of the sarcoma patients responded to radiosurgery. After a follow-up of 28 to 67 months, 4 of 5 patients are alive. This investigation demonstrates that radiosurgery is an effective tool in palliative treatment for patients who have recurrent, extensively pretreated nasopharyngeal cancer. Patients who have recurrent sarcomas of the base of skull may be treated for long-term palliation or even for cure.

Transfer of information between angiographic films and CT images: a technique to control the drawing of target volumes

BACKGROUND AND PURPOSE

This work was undertaken to improve the definition of target volumes for radiosurgery using the angiographic and CT data.

MATERIALS AND METHODS

The basis of this new method is to combine both imaging modalities and to compare them in each representation, i.e. to plot the volume obtained by angiography on CT images and also the contours defined by the CT on angiographic films. To obtain the angiographic volume, the radiographs are taken at several incidence angles. The X-ray sources position and the position of the films are determined using rectangular markers, then the intersection of all the loci of the target volume are calculated.

RESULTS

Verifications with a phantom show the accuracy of the procedure and the benefit obtained by increasing the number of angles of incidence in the angiographic imaging. The centre of gravity of the experimental target could be localized to an accuracy of better than 0.4 mm. The method was used in 11 clinical cases with excellent clinical results.

CONCLUSIONS

The method can be easily applied and improves the delineation of target volumes in radiosurgery. CT data counterbalances the relative weakness of angiography concerning the three-dimensional geometry. Angiography adds useful information on the blood flow that is not shown in CT. Almost all the presented clinical cases benefit from the technique described here.

Dose-response relationship for late functional changes in the rat brain after radiosurgery evaluated by magnetic resonance imaging

PURPOSE

Only few quantitative data are available on late effects in the healthy brain after radiosurgery. An animal model can contribute to systematically investigate such late effects. Therefore, a model applying radiosurgery at the rat brain was established. A long-term (19 months) follow up study with 66 animals after radiosurgery was carried out.

METHODS AND MATERIALS

In 60 animals, an area in the frontal lobe of the brain was irradiated stereotactically with a 15 MV linac. Different doses of 20, 30, 40, 50, and 100 Gy with two field sizes (3.9 and 5.9 mm collimator) were selected, using the integrated logistic formula with input parameters from human brain. The induced alteration of the blood-brain barrier permeability was investigated by means of contrast enhanced magnetic resonance imaging.

RESULTS

A first intracranial signal enhancement was observed in one animal 160 days after irradiation with 100 Gy. Beginning at 5 months all animals in the two 100 Gy groups homogeneously showed contrast enhancement, but none of the other groups. This remained until 13 months after irradiation. The volume of contrast enhancement as well as the increase of signal intensity were different between the two 100 Gy groups. After 19 months, the animals irradiated with lower doses also showed contrast enhancements, although not uniformly throughout one group. A maximum likelihood fit of the logistic formula P(D) = 1/[1 + (D50/D)k] to the incidence of late effects for the 5.9 mm collimator at 19 months after irradiation results in the parameters D50 = 37.4(-5.2,+6.1) Gy and k = 4.7 +/- 2.4.

CONCLUSIONS

An animal model was established to study late normal brain tissue response. The observed late effects appeared very similar to the estimation of the integrated logistic formula for human brain. Based on these radiosurgery techniques, future experiments will focus on modifications in the irradiation modalities, i.e., irregular volumes, radiation quality or fractionation.

Cystic craniopharyngioma: long-term results after intracavitary irradiation with stereotactically applied colloidal beta-emitting radioactive sources

OBJECTIVE

Long-term follow-up data were analyzed to assess the value of intracavitary irradiation with stereotactically applied beta-emitting radioisotopes for the treatment of craniopharyngioma cysts.

METHODS

Sixty-two of 70 consecutive patients with predominantly cystic craniopharyngiomas were selected for retrospective analysis. Beta-Emitting isotopes were injected intracystically using a computed tomography-guided and computer-assisted three-dimensional stereotactic treatment planning and application system (cumulative dose to the inner surface of the cyst wall, 200 Gy).

RESULTS

The tumor response rate gained with yttrium-90-labeled silicate (66 of 78 cysts) or phosphorous-32-labeled chromic phosphate (8 of 78 cysts) was 79.5%. Four cysts treated with rhenium-186-labeled sulfate did not respond. Mean survival after intracavitary irradiation was 9.0 +/- 0.9 years (median follow-up, 11.9 yr). In patients with solitary cysts, the mean survival was 12.5 +/- 1.4 years (actuarial 5- and 10-yr survival rates, 80 and 64%, respectively). Six months postoperatively, visual deficits (38 of 62 patients) had improved in 23 patients and were stable in 15 patients. The side effects that occurred 6 to 12 months after treatment with yttrium-90 were complete blindness (three patients), worsening of visual field cuts (one patient), third nerve palsy (one patient), and diabetes insipidus and/or panhypopituitarism (three patients).

CONCLUSIONS

Intracavitary irradiation using yttrium-90 or phosphorous-32 is highly effective in the treatment of cystic craniopharyngiomas. If applied as initial treatment in patients with solitary cysts, it is the only required therapy over a long period.

Risk analysis of LINAC radiosurgery in patients with arteriovenous malformation (AVM)

The purposes of this analysis were the evaluation of the toxicity of stereotactic single dose irradiation in patients with an arteriovenous malformation (AVM) and the comparison of the authors' own results with already existing risk prediction models. Computed-tomography (CT) or magnetic-resonance (MR) images, and clinical data of patients treated with linear accelerator radiosurgery for an AVM were analysed retrospectively. Using the Cox proportional hazards model (1), the relevance of treatment parameters and dose-volume relationships to the occurrence of radiation-induced tissue changes (oedema and localised blood-brain-barrier breakdown) were assessed. The 81 patients selected for analysis had a mean follow-up of 28.9 months (range: 9.0-65.7 months). Radiation-induced tissue changes (22 out of 81 i.e. 27.2%) were documented on CT or MR images 6.3-33.8 months after radiosurgery (median time: 12.8 months). The actuarial risk at 2 years was 32.1% for the development of neuroradiological changes and 20.1% for the development of symptomatic tissue alteration. The coefficient of total volume receiving a minimum dose of 10 Gy (VTREAT10) reached statistical significance in a Cox proportional hazards model. These results demonstrate the particular vulnerability of normal brain tissue to single dose irradiation. Optimal conformation of the therapeutic isodose line to the 3D configuration of the target volume may help to reduce side effects.

Risk analysis of linear accelerator radiosurgery

PURPOSE

To evaluate the toxicity of stereotactic single-dose irradiation and to compare the own results with already existing risk prediction models.

METHODS AND MATERIALS

Computed tomography (CT) or magnetic-resonance (MR) images, and clinical data of 133 consecutive patients treated with linear accelerator radiosurgery were analyzed retrospectively. Using the Cox proportional hazards model the relevance of treatment parameters and dose-volume relationships on the occurrence of radiation-induced tissue changes (edema, localized blood-brain barrier breakdown) were assessed.

RESULTS

Sixty-two intraparenchymal lesions (arteriovenous malformation (AVM): 56 patients, meningioma: 6 patients) and 73 skull base tumors were selected for analysis. The median follow-up was 28.1 months (range: 9.0-58.9 months). Radiation-induced tissue changes (32 out of 135, 23.7%) were documented on CT or MR images 3.6-58.7 months after radiosurgery (median time: 17.8 months). The actuarial risk at 2 years for the development of neuroradiological changes was 25.8% for all evaluated patients, 38.4% for intraparenchymal lesions, and 14.6% for skull base tumors. The coefficient: total volume recieving a minimum dose of 10 Gy (VTREAT10) reached statistical significance in a Cox proportional hazards model calculated for all patients, intraparenchymal lesions, and AVMs. In skull base tumors, the volume of normal brain tissue covered by the 10 Gy isodose line (VBRAIN10) was the only significant variable.

CONCLUSIONS

These results demonstrate the particular vulnerability of normal brain tissue to single dose irradiation. Optimal conformation of the therapeutic isodose line to the 3D configuration of the target volume may help to reduce side effects.

LINAC-radiosurgery (LINAC-RS) in pituitary adenomas: preliminary results

From 8/90 through 4/94, 32 consecutive patients with recurrent pituitary macroadenoma (PA) were treated with LINAC-RS after tumour resection and/or radiotherapy. Single doses ranging from 8-20 Gy (median: 14.5 Gy) were applied in 14 patients with acromegaly, 5 with Cushing's disease, 4 with Nelson tumours, 5 with prolactinomas and in 4 with nonfunctioning PA's. Retrospective analysis of 26 patients with a follow-up of > or = 6 months revealed no significant endocrinologic response in patients with Cushing's disease, Nelson tumour or prolactinoma. In contrast in 12 evaluated patients with acromegaly within 6-36 months after LINAC-RS the median GH-value decreased significantly. In 3 nonfunctioning PA's a tumour volume reduction has been observed. We conclude, that LINAC-RS with moderate single doses might be a safe and beneficial treatment in patients with acromegaly or nonfunctioning PA's resistant to conventional therapy. In Cushing's disease, Nelson tumours or prolactinomas higher doses seem to be required.

Target point calculation in the computerized tomography. Comparison of different stereotactic methods

The adaptation of computerized tomography for stereotactic operations requires the transformation of the coordinates of the target point from the CT image space into the stereotactic frame space. Two basic solutions for this transformation are realized in the most of the contemporary stereotactical systems. The indirect geometric method adjusts the frame coordinate system mechanically and identifies its origin in the CT image. There are 6 degrees of freedom: 3 of rotation and 3 of translation which have to be taken into consideration. The second method is a based on direct algebraic coordinate transformation and is independent of the explicite knowledge of the relationship between the image and the frame space. A localization frame serves to determine a transformation matrix which, applied to any point in the image, transforms the coordinates directly into the frame coordinate system. Only the algebraic method is independent of the position of the patient in the gantry. All other methods require high mechanical precision of the alignment and stability for the CT table.

Stereotactic convergent beam radiosurgery versus stereotactic conformation beam radiotherapy

By means of preliminary results in the treatment of patients with acoustic neurinoma the achievable accuracies, dose distributions and time consumption of stereotactic LINAC-based convergent beam radiosurgery are compared to those achieved with fractionated stereotactic conformation beam radiotherapy. Characteristics of both techniques are described. With the Tübingen radiosurgery system a good adaptation of the dose distribution to spherical or oval target volumes with a steep dose gradient was achieved, whereas homogeneity and adaptation of the dose distribution to irregularly shaped targets were better with the Heidelberg conformation technique. The mechanical accuracy of the Tübingen floorstand system was 0.3 mm +/- 0.2 mm, and that of the Heidelberg mask fixation system < 1 mm. Both methods require similar total treatment times. Nine patients were treated by the Tübingen radiosurgery system. The results are compared with 12 patients treated by conformation radiotherapy in Heidelberg. In both patient groups no further tumour growth occurred. Four of 9 single dose treated patients developed side-effects, such as temporary trigeminal and facial paraesthesia hearing deterioration and oedema. In contrast, patients treated by fractionated radiotherapy showed no side-effects. Relating to the short follow-up the results indicate that single dose application has certain drawbacks for special indications. Further studies have to work out which method gives the best treatment results.