直肠癌术前放疗中XVMC算法和MC算法剂量差异分析

Dosimetric differences between XVMC algorithm and MC algorithm in preoperative radiotherapy for rectal cancer

目的:评估直肠癌术前放疗中,使用X射线体素蒙特卡罗(XVMC)算法与ArcherQA中蒙特卡罗(MC)算法获得的剂量分布数据的差异,为临床上XVMC算法的计划评估提供参考。方法:对10例直肠癌术前放疗的患者,采用MONACO计划系统中的XVMC算法制定计划。将计划中制定好的CT、组织结构和射野信息传入MC软件,运用MC算法进行二次剂量计算。比较XVMC算法与MC算法间靶区和各危及器官的剂量差异。结果:XVMC和MC算法计算的中心点剂量,计划靶区(PTV)的D_(min)和D_(mean)、小肠的V_(40)、膀胱的D_(mean)和V_(45)、股骨头的D_(mean)差异均在2%以内。PTV、脊髓外扩和小肠三者的D_(max)在两种算法的差异分别为3.43%、3.59%和3.62%;PTV的V_(5040)差异为2.87%。结论:XVMC较MC算法低估了计划的剂量最大量,高估了靶区的处方剂量覆盖率,但两种算法之间的差异为临床可接受的范围内(5%以内),计划评估时需注意因算法所带来的剂量计算误差。

Objective To evaluate the difference in dose distribution calculated using X-ray voxel Monte Carlo(XVMC)algorithm and ArcherQA Monte Carlo(MC)algorithm in preoperative radiotherapy for rectal cancer,thus providing reference for the planning and evaluation of XVMC algorithm in clinical practice.Methods For 10 patients with rectal cancer undergoing preoperative radiotherapy,the XVMC algorithm in MONACO planning system was used to develop the plan.The CT,tissue structure,and field information from the prepared plan were transmitted to Monte Carlo software,and the MC algorithm was used for the secondary dose calculation.The dose differences between XVMC algorithm and MC algorithm in the target area and organs-at-risk dose calculations were analyzed.Results The differences in D_(min) and D_(mean) of the planning target volume(PTV),V_(40) of the small intestine,V_(45) and D_(mean) of the bladder,and D_(mean) of the femoral head calculated by XVMC and MC algorithms for isocenter dose were all within 2%.The differences in the D_(max) of PTV,spinal cord expansion,and small intestine between two algorithms were 3.43%,3.59%,and 3.62%,respectively;and the difference in the V_(5040) of PTV was 2.87%.Conclusion XVMC algorithm underestimates the planned maximum dose and overestimates the prescription dose coverage in the target area as compared with MC algorithm,but the dosimetric differences between the two algorithms are within a clinically acceptable range(within 5%).When evaluating the plan,attention should be paid to the dose calculation errors caused by the algorithm.