@misc{oai:niigata-u.repo.nii.ac.jp:00005295,
 author = {早川, 岳英},
 month = {Mar},
 note = {The purpose of this study, improving the calculation accuracy of the system to be used for independent monitor unit (MU) verification of the safety check in clinical radiotherapy using X-ray of linear accelerator (linac). Current, treatment planning systems (RTPS) is used for calculate the MU value and to predict the internal dose from computed tomography (CT) images. And it has a problem due to the accidents caused by the abnormal MU value in operation by the user's misunderstanding of high performance RTPS. Therefore, RTPS's MU is necessary to confirm in independent verification, that is to check for tolerance between RTPS's MU and independent verification MU. This paper is focused on method of manual calculation of independent verification, we investigated the output factor estimation of parameters required to MU calculation. The output factor is a function of the change in dose for a field size of the linac. At the simple rectangle field, the area perimeter ratio (Area/Perimeter;A/P) method can convert the radiation field into dose equivalent square field, and the A/P method can be estimated accurately the output factor at arbitrary rectangular field. However, A/P method can not accurately estimate the output factor at the multileaf collimator (MLC) with irregular field in clinical. Thus, the output factor is represented by total scatter factor (S_<c,p>), it adopted a method by multiplying the collimator scatter factor (S_c) and the phantom scatter factor (S_p). First, We proposed the approximation model considering the physical properties of each of S_c and S_p. S_c is depend on the width X and height Y of the radiation field, thus we proposed the approximation model with the variables X and Y. S_p is depend on distance of the center and edge of the radiation field (equal to the radius), thus we proposed the approximation model with a variable radius. Second, the measured values of S_c and S_p at the rectangle field was measured in phantom, then the model parameters will be determined by least-squares curve fitting. As a result, the approximation model fit is good with measurements of S_c, it was found that the approximation model with variables X and Y, S_c value of arbitary rectangular field may be accurately estimated. Also, the approximation model fit is good with measurements of S_p, it was found that the approximation model with a variable radius, S_p value of arbitary rectangular field may be accurately estimated. Finally, the proposed method compares the measured and estimated values of S_c and S_p in with the MLC irregular field in the phantom. And the accuracy of the proposed method was confirmed in clinical irregular field. In this paper, we investigated estimation of the output factor in the calculation of the independent MU verification in clinical radiotherapy using X-ray. We proposed the approximation model of the collimator scatter factor (S_c) and the phantom scatter factor (S_p), and confirmed those proposed method was useful. It can expect improvement of the calculation accuracy when the clinical system of independent MU verification including the method of this study., 本研究の目的は,リニアックX線治療の線量単位であるモニターユニット(MU)値の安全確認に使用する独立検証システムの計算精度向上である.現在は,CT画像から線量を予測して治療計画装置(RTPS)でMU値を計算するが,RTPSの高性能化伴い誤った認識と操作ミスが原因の異常なMU値による誤照射事故が問題となっている.そのため,RTPSとは独立した別手段でもMU値を計算し,両者のMU値が許容誤差内か確認することで安全性を確保する独立検証が必要になっている.本論文は,独立検証の一方法の手計算による検証に着目し,そのMU値計算に必要なパラメータの出力係数の推定法を検討した.出力係数はリニアックの照射野サイズに対する線量変化を表す関数で,単純な矩形照射野の照射では,面積周囲長比(Area/Perimeter)から線量等価な正方形照射野に換算するA/P法により,任意の矩形照射野の出力係数を正確に推定できる.しかし,臨床的なマルチリーフコリメータ(MLC)を使った不整形照射野の照射では,A/P法によると出力係数を正確に推定できない.そのため,出力係数を全散乱係数S_<c,p>で表し,それをコリメータ散乱係数S_cとファントム散乱係散S_pに分ける方法を採用した.まず,S_cとS_pのそれぞれの物理的特性を考慮した近似モデルを提案した.S_cは照射野の幅Xと高さYに依存するため,XとYを変数とする近似モデルを作成した.S_pは照射野中心から辺縁までの距離(半径)に依存するため,半径rを変数とする近似モデルを作成した.次に,ファントムで測定した矩形照射野のS_cとS_pの測定値に,最小2乗法でカーブフィットさせてモデルパラメータを求めた.その結果,S_cの測定値と近似モデルのフィットは良好で,XとYを変数として任意の矩形照射野のS_cを正確に推定できることが分かった.また,S_pの測定値と近似モデルのフィットは良好で,rを変数として任意の矩形照射野のS_pを正確に推定できることが分かった.最後に,ファントムで測定したMLCを使った不整形照射野におけるS_cとS_pの測定値と提案法による推定値とを比較し,臨床的な不整形照射野において提案法の正確さを確認した.本論文では,リニアックX線治療のMU値独立検証の計算に必要な出力係数の推定に関し,コリメータ散乱係数S_cおよびファントム散乱係数S_pの近似モデルを提案し,それぞれのモデルによる推定法の有用性を確認した.本方法を臨床のMU値独立検証システムに組み込むと,計算精度の向上が期待できる., 新潟大学大学院自然科学研究科, 平成24年3月23日, 新大院博（工）甲第381号, 新大院博（工）甲第381号},
 title = {放射線治療におけるモニターユニット値独立検証のパラメータ推定に関する研究},
 year = {2012}
}