圓柱型相位陣列超音波換能器應用於乳癌熱手術之研究

Abstract

本研究的目的為探討圓柱型相位陣列超音波換能器搭配多聚焦點模式掃描之加熱策略應用於乳癌熱手術之可行性。在本研究中，乳房被一個驅動頻率為1MHz的圓柱型相位陣列超音波換能器所環繞，半徑為10㎝、高2㎝，而其包含了200個獨立驅動的單元晶片。為了避免在治療時傷害過多的正常組織，一個1㎝×1㎝的目標區域被選定為單一治療單元。若是目標區域的大小大於單一治療單元的大小，則會將目標區域切割為數個子治療單元，並依序分別進行加熱，並且在各個子治療單元之間給予冷卻的時間，以降低對周圍的正常組織之傷害。同時亦討論治療參數：目標溫度（Ttgt）、血液灌流率以及目標區域之大小之影響。除此之外，也針對一個淺層乳房腫瘤（腫瘤邊界距離皮膚約5㎜）在不同周圍冷卻水初始水溫下之治療情形進行探討。模擬結果顯示，目標溫度的高低（Ttgt）會影響燒灼區域的大小，而較高的血液灌流率則會使加熱時間顯著的延長。基於圓柱型相位陣列超音波換能器擁有較大的聲窗口搭配上周圍冷卻水所帶來的冷卻效應，由模擬結果可以得知，以本系統進行淺層乳房腫瘤治療時，可以在目標區域產生一個可接受的燒灼結果，而不會有皮膚過熱或燒傷的現象。本研究中所提出的圓柱型相位陣列超音波換能器系統以及加熱策略為乳房腫瘤之熱手術提供了一個有效的治療方法，並且可以大幅減低肋骨以及皮膚發生過熱的情形。

The purpose of this study is to investigate the feasibility of a cylindrical ultrasound phased-array with multiple-focus scanning strategy to produce a uniform heating for breast thermal therapy. In this study, a breast is surrounded by a 1-MHz cylindrical ultrasound phased-array consisting of 200 elements with a radius of 10 cm and a height of 2 cm. To prevent overheating in the normal tissue, a scanning heating region of 1㎝×1㎝ was selected as a single heating unit. Planning target volume larger than this size would be divided into several sub-heating units, and then be treated sequentially with cooling phase between heating sub-units to prevent overheating in the surrounding normal tissue. Parameters such as the target temperature（Ttgt）, blood perfusion rate and the size of the planning target volume are evaluated. Furthermore, a case of superficial breast tumor （The distance from tumor boundary to the skin is about 5㎜.） was simulated with different surrounding water temperature：37 and 20℃. Simulation results show that the target temperature affects the thermal lesion size and the blood perfusion rate increases the heating time significantly. Due to large acoustic window and the effect of surrounding cooling water, the lesion was well produced in the desired region without skin overheating. This method provides effective heating for breast tumor thermal therapy while preventing overheating the ribs and skin.