Bragg Christopher M, Wingate Katrina, Conway John
Department of Radiotherapy Physics, Weston Park Hospital, Sheffield, UK.
Radiother Oncol. 2008 Feb;86(2):276-84. doi: 10.1016/j.radonc.2008.01.011. Epub 2008 Feb 4.
To determine the implications of the use of the Anisotropic Analytical Algorithm (AAA) for the production and dosimetric verification of IMRT plans for treatments of the prostate, parotid, nasopharynx and lung.
72 IMRT treatment plans produced using the Pencil Beam Convolution (PBC) algorithm were recalculated using the AAA and the dose distributions compared. Twenty-four of the plans were delivered to inhomogeneous phantoms and verification measurements made using a pinpoint ionisation chamber. The agreement between the AAA and measurement was determined.
Small differences were seen in the prostate plans, with the AAA predicting slightly lower minimum PTV doses. In the parotid plans, there were small increases in the lens and contralateral parotid doses while the nasopharyngeal plans revealed a reduction in the volume of the PTV covered by the 95% isodose (the V(95%)) when the AAA was used. Large changes were seen in the lung plans, the AAA predicting reductions in the minimum PTV dose and large reductions in the V(95%). The AAA also predicted small increases in the mean dose to the normal lung and the V(20). In the verification measurements, all AAA calculations were within 3% or 3.5mm distance to agreement of the measured doses.
The AAA should be used in preference to the PBC algorithm for treatments involving low density tissue but this may necessitate re-evaluation of plan acceptability criteria. Improvements to the Multi-Resolution Dose Calculation algorithm used in the inverse planning are required to reduce the convergence error in the presence of lung tissue. There was excellent agreement between the AAA and verification measurements for all sites.
确定使用各向异性分析算法（AAA）对前列腺、腮腺、鼻咽和肺部治疗的调强放疗（IMRT）计划进行生成和剂量验证的意义。
使用笔形束卷积（PBC）算法生成的72个IMRT治疗计划，使用AAA重新计算并比较剂量分布。其中24个计划被用于非均匀模体，并使用针点电离室进行验证测量。确定AAA与测量结果之间的一致性。
在前列腺计划中观察到小的差异，AAA预测的PTV最小剂量略低。在腮腺计划中，晶状体和对侧腮腺剂量有小的增加，而在鼻咽计划中，当使用AAA时，95%等剂量线覆盖的PTV体积（V(95%)）有所减少。在肺部计划中观察到较大变化，AAA预测PTV最小剂量降低，V(95%)大幅降低。AAA还预测正常肺的平均剂量和V(20)有小的增加。在验证测量中，所有AAA计算结果与测量剂量的距离一致性在3%或3.5毫米以内。
对于涉及低密度组织的治疗，应优先使用AAA而非PBC算法，但这可能需要重新评估计划可接受性标准。需要改进逆向计划中使用的多分辨率剂量计算算法，以减少肺部组织存在时的收敛误差。AAA与所有部位的验证测量结果之间具有良好的一致性。
