在乳房攝影中量測可壓迫假體之影像品質與輻射劑量

Measurement of image quality and radiation dose of compressible breast phantoms in mammography

王亭尹(Ting-Yin Wang)

指導教授 ： 董尚倫

中山醫學大學/醫學科技學院/醫學影像暨放射科學系碩士班/碩士(2018年)

摘要

前言
目前臨床常用在乳房攝影的影像品質測試與輻射劑量評估假體多為硬性的剛體結構，無法如實反映真實乳房接受數位式乳房斷層攝影(digital breast tomosynthesis, DBT)過程、臨床條件、影像品質與輻射劑量，本研究目的為使用可壓迫之Bolus假體評估數位式乳房斷層攝影系統的影像品質與輻射劑量。
材料與方法
本研究以Selenia Dimensions (Hologic)DBT系統進行攝影，分別使用CDMAM假體(Artinis CDMAM 3.4)與熱發光劑量計(thermoluminescent dosimeter, TLD) TLD-100 microcubes(Harshaw/Bicron, Solon, OH)進行影像品質與輻射劑量之量測。在影像品質評估方面，首先分別堆疊4-8公分Bolus假體(MT-CB-410S, CIVCO, Medical Solution, France)，並搭配CDMAM假體進行攝影，其次請3位觀測者對每組所得之FFDM與SM影像進行閱片判讀。在乳房假體之劑量分布評估方面，首先分別堆疊3-10公分Bolus假體，並將TLD-100 microcubes包埋於Bolus假體之不同深度中，進行FFDM與DBT攝影後，計讀TLD的讀值轉換成劑量以測得深度劑量分布。在臨床應用方面，首先分別包摺4-8公分厚的Bolus假體，並在假體之上、中、下層中包埋TLD-100 microcubes，其次分別以58.8-156.8 N的壓力對每組假體加壓後進行DBT攝影，最後藉由DBT的切面影像計算得到TLD之深度位置，同時量測TLD所計讀到的劑量，以測得受壓迫假體內的深度劑量。
結果
在影像品質評估方面，FFDM影像的正確觀測率(correction observation ratios,COR)優於SM影像，以6公分Bolus假體為例，其FFDM與SM影像之COR分別為48.2%、35.1%。在輻射劑量評估方面，量測劑量隨TLD-100 microcubes深度位置加深而下降，以6公分Bolus假體為例，其FFDM與DBT攝影之劑量範圍分別為0.61-5.46 mGy與0.92-5.55 mGy。在臨床應用方面，TLD-100 microcubes的深度位置隨施加壓力增加而降低，且假體中間層之量測劑量相當於其平均乳腺劑量(average glandular dose, AGD)。
結論
本研究發現在厚度較厚之可壓迫假體，其FFDM之影像品質優於SM之影像品質。對厚度較厚之可壓迫假體而言，改變施加壓力對輻射劑量會造成顯著影響。因此，Bolus假體與TLD-100 microcubes應是適合用於量測臨床DBT系統的影像品質與輻射劑量之工具。

關鍵字

數位式乳房斷層攝影 ； 影像品質 ； 輻射劑量 ； TLD-100 microcubes

並列摘要

Purpose
At present, the rigid-type breast phantoms are frequently used for assessments of image quality and radiation dose in mammography. These breast phantoms cannot accurately simulate imaging factors, image quality, and radiation dose under clinical compression procedures in digital breast tomosynthesis (DBT). The purpose of this study is the measurement of image quality and radiation dose in DBT using compressible breast phantom.
Materials and methods
The DBT system (Selenia Dimensions, Hologic) was used in this study. The contrast-detail mammographic phantom (Artinis CDMAM 3.4) and the thermoluminescent dosimeter TLD-100 microcubes (Harshaw/Bicron, Solon, OH) were used for measuring image quality and radiation dose, respectively. To measure the image quality, 4-8 cm Bolus phantoms (MT-CB-410S, CIVCO, Medical Solution, France) with the CDMAM were irradiated and the CDMAM images were constructed with FFDM and SM mode. These CDMAM images were read and scored by three observers. To measure the radiation doses, 3-10 cm Bolus phantoms with 50 microcubes of TLD-100 were irradiated under FFDM and DBT modes. The TLDs were placed in the different depths of the Bolus phantoms for the assessment of depth dose distribution. In the clinical compression applications, the 4-8 cm Bolus phantoms with TLDs were compressed with forces of 58.8-156.8 N. The depth of each TLD in the Bolus phantom was investigated using the sectional image of DBT and the dose of each TLD was measured.
Results
In the assessment of image quality, the correction observation ratios of CDMAM images of FFDM was those of CDMAM images of SM mode. For example, the correction observation ratios of CDMAM images with the 6-cm Bolus phantom for FFDM and SM modes were 49.4% and 35.1%, respectively. In the assessment of radiation dose, the measured dose decreased with the increasing depth of TLD. For example, the measured doses of TLDs in the 6-cm Bolus phantom for FFDM and DBT modes were 0.61-5.46 and 0.92-5.55 mGy, respectively. In the clinical application, the depth of TLD decreased with the increasing compression forces. The measured doses of TLDs around the central layer were comparable to the average glandular dose (AGD) of the compressible breast phantoms.
Conclusion
Results from this study demonstrated that the image quality of FFDM is superior to that of SM for a compressible breast phantom with large thickness. We also observed that the impact on radiation doses caused by changing compression forces is significant for a compressible breast phantom with large thickness. Therefore, the Bolus phantoms and TLD-100 microcubes are suitable for the measurements of the image quality and radiation dose in different clinical DBT applications.

並列關鍵字

digital breast tomosynthesis ； image quality ； radiation dose ； TLD-100 microcubes

參考文獻

[1] 衛生福利部國民健康署，中華民國104年癌症登記報告(2017/12/27發布)

[2] Carol DeSantis, Jiemin Ma, Leah Bryan and Ahmedin Jemal. Breast Cancer Statistics, 2013. CA: A Cancer journal for Clinicians banner 2014; 64: 52-62.

[3] Thomas M. Beck, Dan Sayam Zuckerman, Paul G. Montgomery, Patty Sproat and Mary Winn. Breast cancer and overall mortality following a diagnosis of ductal carcinoma in situ (DCIS) at major community cancer center: A report of 1,014 cases. Journal of Clinical Oncology 2016; 34: 15_suppl, e12015-e12015.

[4] Sopik, Victoria, MSc; Narod and Steven, A. DCIS and Breast Cancer: Challenging the Paradigm. Annals of Surgery 2018; 268(1): e17.

[5] Steven A. Narod, Javaid Iqbal, Vasily Giannakeas, Victoria Sopik and Ping Sun. Breast Cancer Mortality After a Diagnosis of Ductal Carcinoma In Situ. JAMA Oncol. 2015;1:888–896.