No abstract available.
Radiosurgery*

No astract is 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

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*

No abstract available.
Meningioma* ; 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*

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

Radiosurgery is a highly precise form of radiation therapy for the treatment of vascular lesions, certain primary or metastatic neoplasms, or functional disorders. Either intracranial or extracranial, which are inaccessible or unsuitable for surgical or other management. As the basis of radiation physics for radiosurgery, this article introduces radiation history, the method of radiation production, interaction mode of radiations with human, transfer of radiation energy to the tissue, and dose planning to generate a desirable dose distribution on the target site. Biologically, the goal of radiosurgery is to cause a precise damage only to the limited tissue within the target volume without exceeding the acceptable rate of complications. As the therapeutic ratio is a function of the volume irradiated, the total dose and dose per fraction used, and the level of acceptable risk, radiation oncologists or practitioners should consider various radiobiologic factors when using radiosurgery to obtain the maximum therapeutic ratio.
Humans ; Radiobiology ; Radiosurgery

PURPOSE: For the purpose of quality assurance of self-developed stereotactic radiosurgery system, a multi-purpose phantom was fabricated, and accuracy of radiation dose distribution during radiosurgery was measured using this phantom. MATERIALS AND METHODS: A farmer chamber, a 0.125 cc ion chamber and a diode detector were used for the dosimetry. Six MV x-ray from a linear accelerator (CL2100C, Varian) with stereotactic radiosurgery technique (Green Knife) was used, and multi-purpose phantom was attached to a stereotactic frame (Fisher type). Dosimetry was done by combinations of locations of the detectors in the phantom, fixed or arc beams, gantry angles (20 ~100 ), and size of the circular tertiary collimators (inner diameters of 10 degrees~40 degrees mm). RESULTS: The measurement error was less than 0.5% by Farmer chamber, 0.5% for 0.125 cc ion chamber, and less than 2% for diode detector for the fixed beam, single arc beam, and 5-arc beam setup. CONCLUSION: We confirmed the accuracy of dose distribution with the radiosurgery system developed in our institute and the data from this study would be able to be effectively used for the improvement of quality assurance of stereotactic radiosurgery or fractionated stereotactic radiotherapy system.
Particle Accelerators ; Radiosurgery* ; Radiotherapy