肺部肿瘤IMRT计划制订过程中不同算法的评估

Evaluation of Two Different Dose Algorithms in IMRT Planning of Lung Tumours

目的:评估AAA算法和PBC算法在肺部肿瘤IMRT计划制订过程中的差异。方法:选取20例肺部肿瘤患者,随机地分配给不同的放疗科医师和物理师进行相关器官的轮廓勾画和IMRT计划制定。对每个病例分别用AAA和PBC两种算法进行剂量计算,并对同一病例所得到的2种IMRT计划进行评估和比较,分析对于不同形态和位置的肺部肿瘤,两种算法的特点和不足。结果:AAA算法在进行复杂结构类型肿瘤的剂量运算时,速度要明显优于PBC算法;同时,AAA算法往往会在高密度体积内得到偏高的吸收剂量,而在低密度体积内得到偏低的吸收剂量,造成AAA算法有时会对位于低密度组织内的肿瘤吸收剂量低于处方剂量,并且提高了位于高密度组织内的正常器官的吸收剂量。结论:在肺部肿瘤IMRT计划制订过程中必须综合考虑肿瘤形态和位置的不同,有根据地选取AAA或者PBC算法来完成计划的制定。

Objective： To evaluate the AAA （analytic anisotropic algorithm） and the PBC （Pencil Beam Convolution）in IMRT planning of lung tumours. Methods： 20 patients with lung cancer were randomly distributed to different medicals and physicists to draw the outline of the structures and complete the pre-made IMRT planning. Dose calculations were performed with both the AAA and the PBC on pre-made treatment plans. The evaluation and comparison were made between the two plans of each patient to make sure the differences of the AAA and the PBC which were used in IMRT planning of lung tumours with different shape and different position. Results： The AAA had proved to be faster to perform the calculations in complex treatment situations compared to the PBC. But in many cases, the AAA was found to overpredict dose beyond low-density heterogeneities and to underpredict dose beyond high-density heterogeneities. In the case of low-density heterogeneities, use of the AAA would result in a dose deficiency with an accompanying reduction in expected tumor control. Where high densities were involved, concerns arose about the possibility of elevated normal-tissue complications. Conclusion ： The deficiency will be notable if the algorithm is chosen blindly in IMRT planning of lung tumours. To choose the valid algorithm for the accomplishment of the plans, the shape and position of the tumours must be considered seriously.