• Radiation Oncology Journal
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• v.8 no.1
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• pp.125-131
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• 1990

In X-ray irradiation, dose distribution depends on multiple parameters, one of them being tissue inhomogeneity to change the dose significantly. considerable dose attenuation through the mid-cranial fossa is expected because of various bony structures in it. Dose distribution around the mid-cranial fossa, following irradiation with 6 MV photon beam, was measured with LiF TLD micro-rod, and compared with the expected dose inthe same sites. In our calculation with $C_f$(correction factor), the expected dose attenuation revealed about $3.74\%$ per 1 cm thickness of bone tissue. And the differences between the expected dose with correction for bone tissue and the measured dose by TLD was small, agreeing within an average variation of $\pm0.21\%$.

• Radiation Oncology Journal
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• v.16 no.3
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• pp.325-335
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• 1998

Purpose : Since the mid cranial fossa is composed of various thickness of bone, the tissue inhomogeneity caused by bone would produce dose attenuation in cobalt-60 gamma knife irradiation. The correction factor for bone attenuation of cobalt-60 which is used for gamma knife source is -3.5$\%$. More importantly, nearly all the radiosurgery treatment planning systems assume a treatment volume of unit density: any perturbation due to tissue inhomogeneity is neglected, This study was performed to confirm the bone attenuation in mid cranial fossa using gamma knife. Materials and Methods : Computed tomography was performed after Leksell stereotactic frame had been liked to the Alderson Rando Phantom (human phantom) skull area. Kodak X-omat V film was inserted into two sites of pituitary adenoma point and acoustic neurinoma point, and irradiated by gamma knife with 14mm and 18mm collimator. An automatic scanning densitometer with a 1mm aperture is used to measure the dose profile along the x and y axis. Results : Isodose curve constriction in mid cranial fossa is observed with various ranges. Pituitary tumor point is greater than acoustic neurinoma point (0.2-3.0 mm vs 0.1-1.3 mm) and generally 14 mm collimator is greater than 18mm collimator (0.4-3.0 mm vs. 0.2-2.2 mm) Even though the isodose constriction is found, constriction of 50$\%$ isodose curve which is used for treatment reference line does not exceed 1 mm. This range is too small to influence the treatment planning and treatment results. Conclusion : Radiosurgery planning system of gamma knife does not show significant error to be corrected without consideration of bone attenuation.