肺癌调强放疗计划AAA算法与PBC算法比较研究

目的 比较Eclipse治疗计划系统笔形束卷积算法(PBC)和各向异性分析算法(AAA)在肺癌调强放疗计划的剂量学差异,并对两种算法进行胸部模体的剂量测量验证。
方法 选取10例肺癌调强放疗计划,分别使用PBC算法与AAA算法进行剂量计算,比较计划靶体积剂量分布及肺和脊髓受量差异。然后将不同算法的治疗计划移植至模体上,对模体内多点进行验证测量,比较计算值与测量值一致性。对两种算法的剂量比较行配对t检验。
结果 与PBC算法相比,AAA算法的计划靶体积D_max更高(t=－4.03,P=0.010)、D_min更低(t=5.09,P=0.040),处方剂量对计划靶体积覆盖体积减小;AAA算法的肺D_mean、V₂₀和脊髓D_max高于PBC算法(t=－3.99、－2.79、－5.46,P=0.010、0.038、0.003)。验证测量结果显示AAA算法计算值与测量值平均偏差<2%,等中心点处优于PBC算法(t=－3.82,P=0.012)。
结论 肺癌调强放疗计划PBC算法高估了靶区剂量、低估了肺和脊髓剂量,因此推荐使用对组织不均匀处理能力更强的AAA算法。

Comparison of pencil beam convolution and anisotropic analytical algorithm for intensity-modulated radiotherapy planning of lung cancer

Objective To compare the dosimetric differences between pencil beam convolution (PBC) and anisotropic analytical algorithm (AAA) in Eclipse treatment planning system for intensity-modulated radiotherapy (IMRT) planning of lung cancer patients and dosimetric verification. Methods 10 IMRT plans of lung cancer patients were calculated using the PBC and AAA and the differences of dosimetric parameter were analyzed according to dose-volume histogram of planning target volume (PTV), lung and spinal cord. The verification measurements were performed on an inhomogeneous thorax phantom using a pinpoint ionization chamber. The agreement between calculated and measured doses was determined. The paired t test was used to compare the results. Results Compared with PBC, the AAA predicted higher maximum PTV dose (t=－4.03,P=0.010), lower minimum PTV dose (t=5.09,P=0.040), and a reduction of the volume of PTV covered by the prescribed dose. The AAA also predicted slightly increases than the PBC algorithm in the mean dose to the lung and the V₂₀ as well as the maximum dose to the spinal cord, and the differences were statistically significant (t=－3.99,－2.79,－5.46,P=0.010,0.038,0.003). In the verification measurements, the agreement between the AAA and measurement was within 2% and superior to the PBC algorithm on isocenter (t=－3.82,P=0.012). Conclusions For IMRT treatment planning of lung cancer, the PBC algorithm overestimates the dose to the PTV and underestimates the dose to the lung and the spinal cord, so the AAA for treating planning in which the tissue inhomogeneous such as lung is present is recommended.