组织等效补偿膜对调强放射治疗的剂量影响

Impact of bolus on intensity modulated radiation therapy dose

目的研究组织等效补偿膜对调强放射治疗(IMRT)的剂量影响。方法选择12例浅表鼻腔癌患者,其中男性7例,女性5例,年龄26～66岁,平均年龄47.7岁。将传统扇形束CT加有虚拟组织等效补偿膜,形成调强计划planA;将调强计划planA移植到做过电子密度刻度的、加有实物组织等效补偿膜的相应锥形束CT(cone-beam CT),直接剂量计算形成planB;将planA复制并去掉虚拟组织等效补偿膜,以同样的靶区处方剂量和目标函数进行优化后剂量计算形成planC。最后将3组计划的剂量体积直方图(DVH)及其统计数据进行对比定量分析。结果①不加组织等效补偿膜的浅表肿瘤调强治疗计划planC中临床靶区(CTV)受量很差,平均V95%为91.4%,且重要器官严重超过耐受剂量,相应的治疗计划根本不能用于临床。②对于IMRTplanA加系统虚拟组织等效补偿膜确实可以增加浅表肿瘤靶区剂量,其CTV平均V95%为99.8%,且能消除计划内高剂量区。③IMRT计划执行时planB中实物组织等效补偿膜虽与虚拟组织等效补偿膜有一定差异,但确实能使肿瘤靶区受到充分的照射剂量,其CTV平均V95%为99.1%,对浅表肿瘤靶区所受的剂量影响较小,对重要器官所受的剂量影响稍较大且不存确定性。结论正确合理地使用组织等效补偿膜进行逆向调强计划优化确实能得到满意的浅表肿瘤剂量分布,并也能使浅表的肿瘤得到很好的放射治疗,但对重要器官所受的剂量影响稍较大且存不确定性。

Objective To explore the impact of bolus on intensity modulated radiation therapy（IMRT） dose.Methods A total of 12 patients with superficial nasal cavity tumor were enrolled,included 7 males and 5 females,who were 26-66 years old with a mean age of 47.7.The traditional fan-beam CT was combined with bolus to form intensity-modulated planA.The intensity-modulated planA was transplanted into the cone-beam CT with electron density scale and physical tissue equivalent compensation film and planB was calculated.The planA was copied with the removal of fictitious bolus,and then optimized to form planCin the same physical objects.The dose volume histogram（DVH） and statistical data of the 3 plans were performed contrast quantitative analysis.Results ①The clinical target volume（CTV） of plan C（superficial tumor without bolus） was poor,the mean V95 %was 91.4 %,and important organs received higher than tolerance dose,indicaed that the correspondeing treatment plan could not be used in clinic.② PlanA（with fictitious bolus） could increase the dose at superficial tumor CTV and eliminated high dose zone,with mean V95 %being 99.8 %.③In IMRT planB,there was difference between fictitious bolus and practical one,and mean V95%was 99.1 %.It had little effect on CTV,but larger dose effect on important organs and uncertainty existed in clinic.Conclusion It is demonstrated that when the bolus is used correctly,superficial tumor could achieve satisfactory dose distribution in IMRT optimization,thus good treatment for superficial tumor could be obtained,but it has larger dose effect on important organs and uncertainty in treatment exists.