No astract is available
Radiosurgery*

No abstract available.
Radiosurgery*

The fi rst part of this study was about measurement of dosimetric parameters for small photon beams to be used as input data for treatment planning computer system (TPS) and to verify the dose calculated by TPS in Stereotactic Radiosurgery (SRS) procedure. The beam data required were percentage depth dose (PDD), off-axis ratio (OAR) and scattering factor. Small beams of 5 mm to 45 mm diameter from a circular cone collimator in SRS were used for beam data measurements. Measurements were made using pinpoint ionisation chamber (0.016cc). In the second part of this study, we reported the important of carrying out quality assurance (QA) procedures before SRS treatment which were found to infl uence the accuracy of dose delivery. These QA procedures consisted of measurements on the accuracy in target localization and treatment room laser alignment. The calculated TPS dose for treatment was verifi ed using pinpoint ionisation chamber and thermoluminescent detector (TLD) 100H. The deviation mean between measured and calculated dose was -3.28%. The measured dose obtained from pinpoint ionisation chamber is in good agreement with the calculated dose from TPS with deviation mean of 2.17%. In conclusion, pinpoint ionisation chamber gives a better accuracy in dose calculation compared to TLD 100H. The results are acceptable as recommended by International Commission on Radiation Units and Measurements (ICRU) Report No. 50 (1994) that dose delivered to the target volume must be within ± 5% error.
Radiosurgery

Stereotactic radiosurgery, including gamma knife radiosurgery (GKS), can in rare cases result in de novo cavernous malformations (CMs). Here, we present a case of de novo CM induced by GKS following treatment of a cerebellar arteriovenous malformation (AVM). A 48-year-old woman was diagnosed with left unilateral Moyamoya disease. Conventional cerebral angiography also revealed an AVM in the left cerebellum. The patient underwent GKS using a 50% isodose of 15 Gy at the margin of the left cerebellar AVM. Magnetic resonance imaging (MRI) taken 3 years after GKS revealed small chronic hemorrhages with perilesional edema in the left cerebellum. Five years later, the lesions became aggravated, but were asymptomatic. Eight years following GKS, the patient was admitted complaining of headache and dizziness. Brain MRI revealed a 1.3cm hemosiderin deposit with an inner hyperintense nodular portion that was enhanced in the left cerebellum. An open craniotomy was performed and the mass was removed, from which pathological findings were compatible with those for CM. The patient recovered to the prehemorrhagic state. This case shows that De novo CMs can rarely develop after radiosurgery. Most CMs have been reported to develop following radiosurgery for brain tumors. As shown in this patient, CMs can also develop after radiosurgery for cerebellar AVM in adults.
Radiosurgery

The purpose of this paper is to develop an efficient method for the quick determination of multiple isocenters plans to provide optimal dose distribution in stereotactic radiosurgery. A Spherical dose model was developed through the use of fit to the exact dose data calculated in a 18cm diameter of spherical head phantom. It computes dose quickly for each spherical part and is useful to estimate dose distribution for multiple isocenter. An automatic computer search algorithm was developed using the relationship between the isocenter move and the change of dose shape, and adapted with a spherical dose model to determine isocenter separation and collimator sizes quickly and automatically. A spherical dose model shows a comparable isodose distribution with exact dose data and permits rapid calculation of 3-D isodoses. The computer search can provide reasonable isocenter settings more quickly than trial and error types of plans, while producing steep dose gradient around target boundary. A spherical dose model can be used for the quick determination of the multiple isocenter plans with a computer automatic search. Our guideline is useful to determine the initial multiple isocenter plans.
Head ; Radiosurgery*

No abstract available.
Meningioma* ; Radiosurgery*

Uveal melanoma is uncommon but life-threatening intraocular malignancy and has been treated by irradiation, local excision and enucleation. Gamma-Knife radiosurgery allows a high dose of radiation to be delivered to an intracranial target with a very high spatial accuracy and has been used for the treatment of ocular melanomas. We have treated two cases of uveal melanoma between October 1994 and December 1999. They include one man and one woman(34, 62 years, respectively). They were followed up for 12 momths. Mean maximal dose was 65Gy. In one case, the tumor disappeared 7 months after gamma-knife radiosurgery. In another case, multiple tumors (uveal, suprasellar and cerebellar tumor) had decreased in size. These results show that single and high dose gamma-knife radiosurgery is may be an option in the local control of uveal melanoma which can spare the eyeball and vision.
Melanoma* ; Radiosurgery*

In this study, we estimated inhomogeneity correction factor in small field. And, we evaluated accuracy of treatment planning and measurement data which applied inhomogeneity correction factor or not. We developed the Inhomogeneity Correction Phantom (ICP) for insertion of inhomogeneity materials. The inhomogeneity materials were 12 types in each different electron density. This phantom is able to adapt the EBT film and 0.125 cc ion chamber for measurement of dose distribution and point dose. We evaluated comparison of planning and measurement data using ICP. When we applied to inhomogeneity correction factor or not, the average difference was 1.63% and 10.05% in each plan and film measurement data. And, the average difference of dose distribution was 10.09% in each measurement film. And the average difference of point dose was 0.43% and 2.09% in each plan and measurement data. In conclusion, if we did not apply the inhomogeneity correction factor in small field, it shows more great difference in measurement data. The planning system using this study shows good result for correction of inhomogeneity materials. In radiosurgery using small field, we should be correct the inhomogeneity correction factor, more exactly.
Electrons ; Radiosurgery

The current LINAC technique for radiosurgery utilizes a single isocenter approach with multiple noncoplanar arcs. This approach results in spherical dose distributions in the target. Many arteriovenous malformations and tumors suitable for radiosurgical treatment have non-spherical or irregular shapes. The basic approach presented in this paper is to use two or multiple isocenters with standard arcs to shape irregular target volumes through the use of multiple spherical targets. Selection of reasonable irradiation parameters in the first stage is critical to the success of real-time optimization. A useful guideline for optimum isocenter separation and collimator size is developed to shape the target margin uniformly with an desired isodose surface for an elongated target. The implementation of multiple isocenters with three dimensional dose model and application of multiple isocenters approach to several cases are discussed.
Arteriovenous Malformations ; Radiosurgery*

No abstract available.
Pituitary Neoplasms ; Radiosurgery