不均等 組織에 對한 6MV X-線의 線量變化와 補償에 關한 實驗的 硏究

Abstract

For the effective radiotherapy, it should always considered that calculation in heterogenous tissue is important particularly with lung which has low density and large volume. To take precise dose distribution in thoracic cage and compensation of dose calculation in heterogenous tissue on 6 Mevx-ray therapy. The author made the thoracic equivalent phantom with parafilm, resin, cork, bone and measured dose distribution with film dosimetry and thermoluminescent dosimetors, and derived empirical equation on tissue peak absorbed ratio and correction for hetergenous tissue with experimental datas. The author defined the correction factors and could compensate very easily using computer program in various irradiation methods for intrathoracic diseases. The results are as followings; 1. Lung density was measured as 0.2-0.4g/㎤ and mean value was 0.28g/㎤. 2. Percent depth dose of lung tissue was increased 2% percentimeter than soft tissue. 3. Percent depth dose of bone tissue was decreased 1.5% per centimeter than soft tissue but it was neglectable to compensate becouse of the small parts of bone in the body. 4. Mean correction factors of thoracic cage depending on lung density, absorbed dose and scattering ratio was 1.14±0.04. 5. The tissue peak absorbed ratio (TPR) of lung tissue was corresponded the TPR of tissue reducing 0.28 times of thickness. 6. In centric rotation, the maximum dose difference between with lung and without lung tissue was calculated in 15% at 180˚ and 240˚ and 5% at 60˚ arc therpy. 7. In eccentric rotation, the center dose was increased 15-20% at 60˚-360˚ rotation in with lung. 8. Isodose curves in various rotation methods were slightly moved to out side direction in with lung but its difference was negligible.;效果的인 妨射線 治療를 위해서는 體內에 吸收되는 線量分布를 正確히 把握하여 予定된 線量을 照射하여야 하지만 骨, 肺組織等 體內 不均等組織에 의한 線量變化는 入射放射線의 에너지와 組織의 減弱係數 및 散亂線量에 의하여 許容誤差以上의 線量變化를 招來하므로 放射線治療의 重要 要因의 하나가 될 수 있다. 著者는 梨花女子大學 附屬病院에서 稼動中인 6MV X線 線型加速器에 의한 組織內 線量變動을 正確히 測定하기 위하여 組織과 等價인 Mix PR, 콜크, 뼈를 이용한 胸部 Phantom을 제작하고 內部에 TLD(Thermoluminescent dosimetor), Ion chamber等 精密한 測定器를 揷入하여 各 部位의 線量을 測定하고 이들의 測定値를 放射線 減弱曲線과 散亂公式에 代入하여 不均等組織에 대한 深部線量率, 組織最大吸收比率(TPR; Tissue Peak Ratio) 및 補正係數에 관한 複雜한 實驗式을 誘導하고 이를 computer programming하므로써 一門, 回轉, 振子照射에 따른 不均等組織의 線量變動을 綜合測定할 수 있었으며 다음과 같은 結果를 얻을 수 있었다. 1) 肺組織의 密度는 0.2에서 0.4g/㎤에 이르며 平均 0.28g/㎤이었다. 2) 肺組織에 대한 深部線量은 같은 두께의 軟組織보다 cm當 2%씩 增加하였다. 3) 骨組識에 대한 深部線量은 같은 두께의 軟組織보다 cm當 1.5%減少되었으나 人體內 骨組織의 分布가 적으므로 臨床上 無視할수 있다. 4) 肺組織에 대한 補正係數는 肺의 密度, 吸收係數 및 散亂比率에 依存하며 胸廓에 대한 平均 補正係數는 1.14±0.04이다. 5) 肺組織에 대한 組織 最大線量點의 比率(TPR)은 肺組織 두께의 0.28倍에 해당하는 軟組織 두께의 TPR과 誤差範圍內(±0.02)에서 一致하였다. 6) 食道部位 照射에서 180°軸(垂直軸)에 대한 肺組織의 線量分布는 振子角 180°와 240°인 경우 中心線量의 變動이 平均 15% 增加하였으며 60°에서는 平均 5%의 變化率을 나타냈다. 7) 한쪽 肺中心 部位 照射에서 90°軸(水平軸)에 대한 線量變化는 振子角(60°-360°)에 따라 平均 15-20% 增加하였다. 8) 回轉照射時, 肺組織의 有無에 따른 深部百分率의 變化에서 90%와 50%인 等量曲線의 移動은 各各 3%, 5%씩 延長되었다.