高强聚焦超声治疗肿瘤的剂量学研究

Study on the dosage of high intensity focused ultrasound treating tumors

高强聚焦超声(HIFU)治疗技术出现在1940年代,到1990年代后进入迅速发展时期,被誉为是21世纪无创治疗肿瘤技术.HIFU无创治疗肿瘤的原理,是利用HIFU声焦域中的高能量短时间内"消融"(ablation)靶区的癌症变组织,同时又不伤及周围的健康组织.HIFU剂量学是关系到HIFU治疗技术能否安全、有效地用于临床的关键问题.本文将对HIFU治疗剂量学的实验和理论研究给出系统论述.HIFU治疗剂量通常称作HIFU辐照剂量,由辐照声强I和辐照时间t共同决定.本文主要研究:(1)I和t各自对热消融靶组织的贡献.研究表明,I与t对靶组织热消融的贡献呈关系式It0.43=C,式中常数C代表热消融组织体积的大小.(2)HIFU辐照剂量与其产生的组织热消融体积之间的定量关系,研究结果表明,组织的消融体积随辐照剂量增大而增大.在较小辐照剂量下,线性声学理论的计算结果与实验结果符合很好;在较高辐照剂量下,消融体积的理论值低于实验值,说明此时需要计及到非线性声学的贡献.(3)组织厚度(表面到靶组织距离)的对消融靶组织体积大小的影响.(4)HIFU剂量学有关消融微米级组织体积的最新研究成果正催生HIFU无创细胞外科技术的出现.

High Intensity Focused Ultrasound(HIFU) technique appeared in the 1940 years and has rapidly developed since 1990s.Now it has been considered as one of the most potential techniques in the 21stcentury for treating tumors.The principle of treating tumors with HIFU is that the high sound energy in focal region of HIFU can be able to ablate the target tumor tissue in a shout time while the surrounding normal tissues are not damaged.HIFU dosage study is a key issue regarding whether the HIFU technique can be applied in clinic safely and effectively.The experimental and theoretical studies on the HIFU therapeutic dosage are discussed here.In the theoretical study O'nell integral equation is used to describe the distribution of the focal sound field and Pannes equation is used to solve the thermal problem of the target tissues.The HIFU therapeutic dose is usually called HIFU irradiation dose determined by two irradiating parameters,namely HIFU irradiation intensity I and HIFU irradiation time t.The main investigation contents in this paper are as follows:(1) Respective contribution of I and t to the target tissue ablation.Based on numerous calculations and compassions,the HIFU dose equation It0.43=C has been attained and here the constant C reflects the dimension of ablating tissue volume.In order to make the ablating tissue volume equal to the focal region volume the C should be 5728W/cm·s0.43.The equation shows that the contributions of I and t to the formation of ablating tissue are different.Suppose,to increase the ablating tissue volume to two times,I should increase to two times with the same t,but the t should increase to five times while the I is kept unchanged.(2) Quantitative relationship between ultrasound irradiation dose and the produced ablating tissue volume.The studied result shows that the ablating tissue volume increases with the irradiation dose increase.The comparison of theoretical and experimental results shows that under smaller exposure dose the calculation result of linear acoustics is in agreement with the experimental result well,but under higher exposure dose the theoretical value appears to be smaller than the experimental one,that means the nonlinear acoustic contribution should be considered in this case.(3) Affect of tissue thickness(from tissue surface to target region) on the target tissue ablation.The research result shows that the ablating tissue volume decreases with the tissue thickness increase under a fixed HIFU emitting dose and the theoretical result is nearly in agreement with the experimental result.(4) The latest research results of HIFU dosage regarding μm order volume ablation is now promoting the appearance of HIFU noninvasive cell surgery.