螺旋断层放疗中虚拟挡块技术对左侧乳腺癌保乳术后患者危及器官的保护效果:三种模式的剂量学比较OA

Objective:To explore the effectiveness of ap-plying different virtual block modes(Allowed,Exit Only and Never)in reducing the dose of organs at risk(OARs)and the impact on treatment efficiency in helical tomotherapy(HT)planning after breast-conserving surgery for left breast cancer.Methods:Data from 21 postoperative patients with left-sided breast cancer who received radiotherapy after breast-conserving surgery were retrospectively analyzed.Three HT plans—Allowed(HTa),Exit Only(HTe),and Never(HTn)—were de-signed for each patient.The dosimetric parameters of the planning target volume and OARs,the monitor units,and the beam-on time(BOT)were compared among the three plans in each patient.Results:In terms of target dose coverage,all three plans met the clinical dose requirements.The coverage V100 and hot spot V107 of HTn were the highest among the three groups(P<0.05),and the conformity index of HTe was superior to HTa and HTn groups(P<0.05).There was no sig-nificant difference in the homogeneity index among the three groups(P>0.05).In terms of organs at risk(OARs)spar-ing,the HTa group demonstrated significantly higher doses/values for all OARs compared to the other two groups,with the exception of heart V20 and V30,and the differences were statistically significant(P<0.05).HTn reduced the median of V5 and V10 of the contralateral lung to 0%,which was significantly lower than that of HTa and HTe groups(P<0.001).The contralateral lung mean dose(Dmean)of the HTe and HTn compared with HTa group decreased by 34.5%and 91.4%,re-spectively(P<0.001).Compared with HTa,the contralateral breast Dmean in the HTe and HTn groups also decreased by 29.6%and 57.7%,respectively(P<0.001).Pairwise comparisons indicated that the liver Dmean and spinal cord Dmax in the HTn were significantly lower than those in the HTe group(P≤0.001),and compared with HTn,there were no signifi-cant differences in V5,V10,and Dmean of the ipsilateral lung and heart in the HTe group(P>0.05).However,compared with HTa,the BOT of the HTn and HTe increased by 179.2%and 39.1%,respectively(P<0.001).Conclusion:The dosimetric parameters of the Allowed mode in HT plans are significantly at a disadvantage.The application of Exit Only mode in the HT plan can effectively reduce the radiation dose of multiple organs without affecting the target area coverage,and the BOT is slightly increased but still within the clinically acceptable range.Never mode can protect OARs to the greatest extent,especially for patients with sensitive contralateral organs or who require extremely low-dose radiation,but the BOT is signifi-cantly prolonged with the lowest efficiency.For clinical application,the block mode(Exit Only or Never)should be selected based on the patient's physical condition,treatment tolerance,and individual differences.