A Study on 3 Dimensional Dose Distribution Calculation System Using Monte Carlo Algorithm for Stereotactic Irradiation

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Monte Carlo is an absorbed dose calculation method which introduce rigorously physical transport theorem in medium. Therefore the Monte Carlo method can calculate not only the absorbed dose in target volume but also the absorbed dose of healthy tissue outside field. For accurate dosimetry, the photon and electron energy spectra for small field of stereotactic irradiation were calculated using Monte Carlo simulation. Furthermore, for accurate dose calculation of stereotactic irradiation, the radiotherapy planning system using Monte Carlo algorithm was developed. Our study can be divided into next 3 categories.1. A study on dosimetry for stereotactic radiotherapyIn stereotactic radiotherapy, a narrow beam is frequently used. Therefore, there are some uncertainties caused by a smaller field than conventional techniques. To estimate error of dosimetry by an ionization chamber caused by variation of energy spectrum of narrow beam, the energy spectra of photons and electrons in water were ca … More lculated using a Monte Carlo simulation. It was evident that photon and electron energy spectra changed as a function of field size and depth in water. The ratios of the mean restricted mass collision stopping power of water to air were determined using the electron energy spectra, and dosmetrical error by variation of energy spectra was discussed.2. Development of 3 dimensional dose calculation system using Monte Carlo algorithm for stereotactic radiotherapyTo clinical use, 3 dimensional dose calculation system using Monte Carlo algorithm was developed. Absorbed dose of the any geometrical condition for stereotactic irradiation can be obtained by this dose calculation system. And calculation parameters were investigated and calculation time was shortened by the several ways.3. Dose distribution analyses for solitary smaU lung cancerThe absorbed dose distributions of solitary lung cancer for several radiotherapy techniques and several incident X-ray energies were analyzed using dose volume histogram. Less