特征线方法(Method of Characteristics,MOC)能否应用于复杂几何关键在于能否将特征线方法与有效的几何处理方法结合起来。本文在菱形差分特征线理论基础上,基于FDS团队自主研发的核与辐射输运计算自动建模软件MCAM的几何处理引擎,研发了基于CAD技术的特征线中子输运计算程序,并利用相关基准例题对程序进行了数值验证,其结果与参考值吻合良好,表明本文方法和程序的可行性、正确性与可靠性。
Optimization of the inverse planning becomes critical because it follows the invention of intensity modulated radiotherapy(IMRT) to shorten the previous "trial-and-error" treatment process and increase efficiency.In this paper, the inverse planning is used to direct aperture optimization in the ARTS(Accurate/Advanced Radiotherapy System). The objective function was quadratic, both tolerance and dose-volume constraint types are supported. The memory efficient conjugate gradient algorithm is used to cope with its large data.Furthermore, to fully exploit the solution space, a shortest path sub-procedure is coupled into the whole algorithm, thus giving further possibility decreasing the objective function. Two clinical cases are tested, indicating that the applicability of this algorithm is promising to clinical usage.
The reliability of radiotherapy was evaluated and effective approaches were obtained in order to improve radiotherapy quality by using the Probabilistic Safety Assessment(PSA) method. This study investigated the feasibility of the PSA method being applied to radiotherapy through Image-guided Radiotherapy(IGRT) and chest tumor irradiation. A fault tree has been constructed after analyzing causal relationship of the events.After calculating Risk A, a total inaccuracy radiotherapy probability and the importance of all base events were obtained. The probability of inaccurate radiotherapy was 2.87%. Under the condition that the target delineation was perfectly right, the accuracy of radiotherapy significantly improved. With the calculation without Conebeam Computed Tomography(CBCT) being corrected before irradiation, the accuracy significantly decreased.The most important events were connected with the human factor. Improving human technical level could enhance radiotherapy quality control efficiently.
