蒙特卡罗方差与通量平滑对乳腺癌VMAT放疗计划的剂量学影响

The Dosimetric effects of Monte Carlo Variance and Fluence Smoothing on VMAT Radiotherapy Plans for Breast Cancer

目的探讨容积旋转调强放疗(VMAT)中不同蒙特卡洛方差(MCV)和通量平滑因子(FSF)组合下的物理参数对VMAT剂量学和放射生物学参数的影响。方法选择2021年1月至2022年12月医院行VMAT治疗的12例左侧乳腺癌根治术后患者为研究对象。通过在Monaco 5.11 TPS中选择不同的MCV选项(0.5%、1%、2%)调整剂量计算误差范围,并通过调整FSF(Low、Medium、High)减少强度分布图噪声,每例患者设计9组放疗计划,分别为Low 0.5、Low 1.0、Low 2.0、Medium 0.5、Medium 1.0、Medium 2.0、High 0.5、High 1.0和High 2.0,共108个放疗计划,以系统默认参数(MCV=1%、FSF=Medium)为对照组,其余纳入试验组。通过剂量-体积直方图(DVH)评估患者靶区和危及器官的剂量学参数,并记录子野数、机器跳数(MU)和治疗时间(T)等物理参数。结果在108个放疗计划中,77.7%的计划满足了将95%的处方剂量覆盖95%靶区的计划靶区(PTV)约束条件,其余计划中超过90%靶区接受95%处方剂量。所有试验组的2%PTV所受剂量(D2%)、平均剂量(D_(mean))、适形性指数(CI)和均匀性指数(HI)与对照组比较,差异均有统计学意义(P<0.05)。在心脏、患侧肺和健侧乳腺剂量学参数方面,MCV值变化对剂量影响较小,而FSF值变化对剂量学和物理参数影响较大,差异有统计学意义(P<0.05)。结论对于左侧乳腺癌术后患者进行VMAT治疗时,通过适当调整MCV值和FSF,可优化放疗方案、减少子野数和T,同时保持剂量覆盖范围,从而提高治疗效率和质量,建议采用MCV为1%、FSF为Low和Medium组合,以获得更佳的剂量学和生物学效果。

Objective To investigate the effects of physical characteristics with different combinations of Monte Carlo variance(MCV)and fluence smoothing factor(FSF)on Volumetric Modulated Arc Therapy(VMAT)dosimetry and radiobiological parameters in VMAT,and to optimize the radiotherapy plan.Methods With the selection of 12 patients with left breast cancer who underwent VMAT radiotherapy plan design in the hospital from January 2021 to December 2022 as the research objects,by selecting different MCV options(0.5%,1%,2%)in Monaco 5.11 TPS to adjust the dose calculation error range,and by by adjusting FSF(Low,Medium,High)to reduce noise in intensity distribution maps,nine radiotherapy plans were designed for each patient,including Low 0.5,Low 1.0,Low 2.0,Medium 0.5,Medium 1.0,Medium 2.0,High 0.5,High 1.0,and High 2.0,totaling 108 radiotherapy plans.The system default parameters(MCV=1%,FSF=Medium 1.0)were used as the control group,while the rest were included in the experimental group.The dosimetric parameters of the patient's target area and organs at risk were evaluated using dose-volume histograms(DVH).Meanwhile,physical parameters such as the number of segments,machine units(MU),and treatment time(T)were recorded.Results Among 108 radiotherapy plans,77.7% of the plans met the PTV constraint of covering 95% of the target volume with 95% of the prescribed dose,and more than 90% of the target volume received 95% of the prescribed dose in the remaining plans.The dose to 2%PTV(D2%),mean dose(Dmean),conformity index(CI)and homogeneity index(HI)of all experimental groups were significantly different from those of the control group(P<0.05).In terms of dosimetric parameters of the heart,affected lung,and healthy breast,changes in MCV values had a relatively small impact on dose,while changes in FSF values had a significant impact on dosimetry and physical parameters,with statistical significance(P<0.05).Conclusions With the design of the VMAT treatment plan for patients with left breast cancer after surgery,by properly adjusting the MCV value and FSF,the radiotherapy plan can be optimized,the segments and T can be reduced,while maintaining the dose coverage,so as to improve the treatment efficiency and quality.It was recommended to use MCV of 1% and FSF as a combination of Low and Medium to obtain better dosimetry and biological effects.