剂量学参数计算方法对治疗计划评估结果的影响分析

目的:分析不同算法对同一个治疗计划进行评估时剂量学参数的变化。 方法:以两种计划系统设计的66例鼻咽癌计划为研究对象，对自主编写评估软件和治疗计划系统读取的剂量学参数结果做比较，研究不同算法下剂量学参数的变化，分析D2和Dmax的差异，并研究D0.01 cc代替Dmax的可行性。 结果:Pinnacle与XiO中读取的剂量学参数与评估软件读取的数据之间存在类似的差异。当器官的体积减小时，Dmax以及Dmean的绝对值偏差都会变大，Dmax的偏差要更大。所有计划中5%的Dmax差值高于292 cGy，5%的Dmean差值高于55 cGy。除PTVnx外，D2的差值平均值都要小于Dmax。相应器官D0.01 cc对应的剂量差值为（45.5±30.4） cGy，Dmax对应的剂量差值为（107.6±56.8） cGy。且除BRAINSTEM_PRV2外，D0.01 cc的剂量差值均小于100 cGy。 结论:用不同的剂量学算法计算同一个治疗计划，Dmax的差异要大于Dmean，体积越小，计算差异一般也越大。用D2代替Dmax可以显著降低计算算法间的差异。用D0.01 cc代替Dmax可以将计算误差显著降低。

Effects of different methods of dosimetry parameter computation on treatment plan evaluation results

Objective To analyze the changes of plan evaluation results when calculating the dosimetry parameters with different algorithms. Methods The treatment plans designed by two different planning systems for 66 cases of nasopharyngeal carcinoma were selected as the research objects. A self-developed evaluation software was adopted to read the dosimetry parameters of the plans, and these results were compared with those obtained with treatment planning system. Then the differences between D2 and Dmax were analyzed, and the feasibility of replacing Dmax with D0.01 cc was discussed. Results Differences between the dosimetry parameters read from Pinnacle and XiO system and the evaluation software were similar. With the reduced volume of the organs, the differences in Dmax and Dmean became larger, and the differences in Dmax were much greater. In all the plans, 5% of Dmax difference was higher than 292 cGy, and 5% of Dmean difference was higher than 55 cGy. Except for PTVnx, the mean value of the differences in D2 was less than Dmax. The dose difference was (45.5±30.4) cGy for D0.01 cc in related organs, and (107.6±56.8) cGy for Dmax. The dose differences of D0.01 cc were less than 100 cGy except for BRAINSTEM_PRV2. Conclusion When calculating the same treatment plan with different methods of dosimetry parameter computation, the differences in Dmax is greater than Dmean. The smaller the volume is, the larger the difference is. The use of D2 instead of Dmax can significantly reduce the difference in the calculation of dosimetry parameters, and replacing Dmax with D0.01 cc can significantly reduce the calculation errors.