通量平滑度对左侧乳腺癌术后胸壁放疗的影响研究

目的:探讨Eclipse放射治疗计划系统上不同的通量平滑度，对左侧乳腺癌根治术后胸壁固定野调强放疗(intensity-modulated radiotherapy,IMRT)计划的剂量学和放射生物学影响。方法:选取2019年04月-2019年12月在我院肿瘤科治疗的20例左侧乳腺癌患者做回顾性分析，基于Eclipse v13.6计划系统对每位患者先使用默认的通量平滑值 (X=40,Y=30) 制定IMRT计划。在相同的优化条件下，改变通量平滑值分别为(X=0,Y=0）、（X=20,Y=15）、（X=80,Y=60）、（X=100,Y=80）重新进行计划设计和评估。将默认的(X=40,Y=30)计划组与其他计划组进行配对t检验，比较靶区的适形指数（conformity index,CI）、均匀性指数（homogeneity index,HI）和危及器官患侧肺、健侧肺、心脏、脊髓、对侧乳腺的剂量学参数、机器跳数、肿瘤控制概率（tumor control probability,TCP）和正常组织并发症概率（normal tissue complication probability,NTCP）。结果:与（X=40,Y=30）计划组相比，只有(X=80,Y=60)、(X=100,Y=80)计划组CI有统计学差异（P＜0.05）；所有计划组HI均有统计学差异（P＜0.05），通量平滑值在(X=40,Y=30)以上增加，CI和HI逐渐变差。危及器官方面，(X=40,Y=30)计划组患侧、健侧肺V5最低，与其他计划组比有显著差异（P＜0.05），(X=40,Y=30)计划组患侧肺V20最低，与(X=20,Y=15)、(X=80,Y=60)、(X=100,Y=80)计划组相比有显著差异（P＜0.05）；心脏V30，V40，Dmean等参数在(X=20,Y=15)以上逐渐升高，且有统计学差异（P＜0.05）。与(X=40,Y=30)计划组相比，其他组脊髓Dmax无统计学意义（P＞0.05）。随着通量平滑值增大，MU最大减小54.6%，降低明显。不同通量平滑组TCP约为90%，且与(X=40,Y=30)计划组相比，除(X=100,Y=80)计划组外其他计划组TCP均无统计学意义（P＞0.05）；患侧肺NTCP除(X=20,Y=15)计划组外其他计划组均有统计学意义（P＜0.05），健侧肺、脊髓和心脏的NTCP无统计学差异（P＞0.05）。结论:在左侧乳腺癌根治术后胸壁固定野调强放疗中，考虑剂量学、放射生物学和计划执行效率，通量平滑值建议采用(X=40,Y=30)。

Effect of fluence-smoothing on left-sided post mastectomy irradiation

Objective:To discuss the effect of different fluence-smoothing on the dosimetry and radiobiology of left-sided post mastectomy fixed-field intensity-modulated radiotherapy(IMRT)in the Eclipse treatment planning system(TPS).Methods:Clinical data of 20 left-sided post mastectomy patients at Zigong First people's Hospital between April 2019 and December 2019 were retrospectively analyzed.Based on the Eclipse v13.6 TPS,each patient was firstly used the default fluence-smoothing value of (X=40,Y=30) to design IMRT plan.In the same optimization conditions,the plans were re-designed and evaluated in other fluence-smoothing values (X=0,Y=0)(X=20,Y=15)(X=80,Y=60)(X=100,Y=80).A paired t test between the default (X=40,Y=30) plan group and other plans was used.The conformity index (CI) and homogeneity index (HI) of the target volume and dosimetric parameters for lungs、heart、spinal cord、contralateral breast were compared.The monitor unit (MU),tumor control probability (TCP) and normal tissue complication probability (NTCP) were also compared.Results:Compared with the（X=40,Y=30）plan,the CI was significantly from the（X=80,Y=60）and（X=100,Y=80）plan groups(P＜0.05).The HI was significantly from all plan groups(P＜0.05).As the fluence-smoothing increased in the default value,CI and HI gradually became worse.In terms of organs at risk,the V5 of lungs for(X=40,Y=30)plan group were the lowest,which was significantly from other plan groups(P＜0.05).The V20 of the affected lung for(X=40,Y=30)plan group was lowest compared with(X=20,Y=15)(X=80,Y=60)(X=100,Y=80)which was significantly from other plan groups(P＜0.05).the cardiac V30,V40,Dmean and other indicators gradually increased over(X=20,Y=15).The spinal cord Dmax was not significantly from(P＞0.05)(X=40,Y=30).As the fluence-smoothing value increased,the number of monitor units MU gradually decreased.The MU was decreased up to 54.6%,and it was statistically significant(P＜0.05)in different groups.The TCP were about 90% for all groups and the TCP except the (X=100,Y=80) plan group was not statistically significant(P＞0.05)when compared with the(X=40,Y=30)plan group,the affected lung NTCP was statistically significant(P＜0.05)in the other plans groups except the(X=20,Y=15)plan group,there was no statistical significant in NTCP of the contralateral lung,spinal cord and heart(P＞0.05).Conclusion:In the left-breast cancer chest wall fixed field intensity-modulated radiotherapy,the fluence-smoothing value is recommended to use (X=40,Y=30) in terms of the dosimetric and radiobiological advantage and plan execution efficiency.