RESUMO
PURPOSE: To find the optimal values of total arc degree to protect the normal brain tissue from high dose radiation in stereotactic radiotherapy planning. METHODS AND MATERIALS: With Xknife-3 planning system & 4 MV linear accelerator, the authors planned under various values of parameters. One isocenter, 12, 20, 30, 40, 50, and 60 mm of collimator diameters, 100degrees, 200degrees, 300degrees, 400degrees, 500degrees, 600degrees of total arc degrees, and 30degrees or 45degrees of arc intervals were used. After the completion of planning, the plans were compared each other using V50 (the volume of normal brain that is delivered high dose radiation) and integral biologically effective dose. RESULTS: At 30degrees of arc interval, the values of V50 had the decreased pattern with the increase of total arc degree in any collimator diameter. At 45degrees arc interval, up to 400degrees of total arc degree, the values of V50 decreased with the increase of total arc degree, but at 500degrees and 600degrees of total arc degrees, the values increased. At 30degreesdegreesof arc interval, integral biologically effective dose showed the decreased pattern with the increase of total arc degree in any collimator diameter. At 45degrees arc interval with less than 40 mm collimator diameter, the integral biologically effective dose decreased with the increase of total arc degree, but with 50 and 60 mm of collimator diameters, up to 400degrees of total arc degree, integral biologically effective dose decreased with the increase of total arc degree, but at 500degrees and 600degrees of total arc degrees, the values increased. CONCLUSION: In the stereotactic radiotherapy planning for brain lesions, planning with 400degrees of total arc degree is optimal. Especially, when the larger collimator more than 50 mm diameter should be used, the uses of 500degrees and 600degrees of total arc degrees make the increase of V50 and integral biologically effective dose. Therefore stereotactic radiotherapy planning using 400degrees of total arc degree can increase the therapeutic ratio and produce the effective outcome in the management of personal and mechanical sources in radiotherapy department.
