環形相位陣列式超音波結合多聚焦型態於乳房腫瘤熱手術之研究

Abstract

此研究的目的為探討環形相位陣列超音波換能器搭配多聚焦點掃描之加熱策略應用於乳癌熱手術之可行性。為了避免在治療時傷害過多的正常組織，一個1.2cm*1.2cm*1cm的目標區域(PTV)被選定為單一治療單元。若是目標區域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時間，以降低對周圍正常組織之傷害。同時亦探討血液灌流率以及腫瘤在不同位置下所造成之影響。除此之外，也針對一個淺層乳房腫瘤在不同周圍冷卻水的狀態下之治療情形進行探討。模擬結果顯示，較高的血液灌流率會減少整體的治療時間，目標區域在偏離乳房中心位置後，熱劑量輪廓有微量的變形。基於環形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均勻治療單元，且有效減少皮膚上的溫升。本研究中所提出的環形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，並且可以大幅降低肋骨以及皮膚發生過熱之情況。

This study investigated the feasibility of using a 0.5 MHz cylindrical phased-array ultrasound transducer with multifocus patterns scanning to produce uniform heating for breast tumor thermal therapy. The breast was submerged in water and surrounded by the cylindrical phased-array ultrasound transducer. Multifocus patterns are electrically scanned by the phased-array to enlarge the treatment lesion in a single heating. To prevent overheating normal tissues, a large planning target volume (PTV) would be divided into several subunits and sequentially treated with a cooling phase between two successive heatings of the subunit. Heating results for different blood perfusion rates and locations of the PTV have been studied. Furthermore, a superficial breast tumor with different water temperatures was also studied. Simulation results show that perfusion rate reduces the treatment time significantly and the location of PTV affects the thermal lesion shape slightly. Due to large acoustic window and the effect of surrounding cooling water, this system was able to achieve a uniform heating without overheating the skin within a short treatment time. This study demonstrated that the proposed cylindrical phased-array ultrasound transducer can provide effective heating for breast tumor thermal therapy without overheating the skin and ribs within a reasonable treatment time.