Digital tomosynthesis for surgical margin assessment in breast-conserving

surgery: Initial Experiences

N. Merchant1, L. Richmond1, M. Skarpathiotakis1, B. Curpen1, R. Jong1, C. Betel1, K. Hack1, A. Maki2 and M. Yaffe1,2

1 Department of Medical Imaging 2 Department of Medical Biophysics Sunnybrook Health Sciences Centre

University of Toronto

Disclosures

  This presentation will discuss the investigational use of a medical device (digital breast tomosynthesis). 

  No other relevant disclosures.

Objectives

  Discuss the rationale and potential role for digital tomosynthesis (DT) in the assessment of gross surgical specimen margins following breast conserving surgery

  Discuss the technical challenges and artifacts encountered

  Discuss potential for future application

Background   Achieving negative surgical margins has important clinical

implications in breast-conserving surgery.

  This is aided by the radiological assessment of the surgical specimen using ultrasound and/or conventional radiography.

Background

Limitations of conventional imaging modalities

  Ultrasound: •  As with breast imaging, limited sensitivity for assessment of certain

lesions, particularly microcalcifications

  Single specimen radiograph: •  Overall sensitivity of 62% and specificity of 95%1

•  2D assessment of an irregularly shaped 3D specimen

•  Allows for assessment of inclusion of the lesion, but not all margins are optimally assessed

•  Overlapping fibroglandular tissue may obscure the lesion(s)

American Journal of Roentgenology. 1994;162(1): 33-36.

Background Digital Tomosynthesis

•  Uses conventional x-rays and a digital detector

•  Images acquired while rotating the x-ray tube in an arc around the breast or a volume of tissue

•  Images manipulated to produce thin slice tomographic cross-sectional images

Digital detector Specimen with wire

Moving X-ray tube

Digital Tomosynthesis (DT)   Over the past decade, Digital Breast Tomosynthesis has been

added to the armamentarium of the Radiologist for breast imaging

  Potential to improve breast specimen margin assessment using 3D imaging vs. the conventional 2D radiograph

To further evaluate this….

We carried out a pilot study to assess the feasibility of using DT to improve the accuracy of surgical specimen margin assessment in cases of radiographically visualized breast lesions.

Pilot Specimen DT study   Single tertiary care oncology centre

  Specialized breast radiologists, surgeons, and pathologists

  Inclusion criteria: patients undergoing preoperative wire localization followed by breast-conserving surgery for mammographically visible lesions including calcifications, masses, masses with calcifications, or clips

  Exclusion criteria: Mastectomy, mammographically occult lesions, and patients unable to give consent

  29 surgical specimens imaged

Specimen DT protocol   DT performed immediately following the

specimen radiograph using the same equipment

  Approximate scan time: 7 seconds

  9 projection images acquired over a 25-degree angular range in a step-and-shoot manner

  Iterative reconstruction algorithm used to produce a reconstructed volume with slices every 0.5 mm in the z-direction

Study methodology   Image reviewer: Radiologist with subspecialty training in

breast imaging

  Anonymized specimen radiographs and DT images reviewed by same reader at separate sittings

  Access to all pre-operative imaging for both sets of imaging reviews, but blinded to the other modality images and the pathology report

  Superior, inferior, lateral and medial margins measured for both imaging modalities

  Pathologic margins used as ground truth

Technical Challenges   Multiple technical challenges and artifacts were encountered

upon review of the DT images

  Led to concerns about variability and reproducibility of the data

  Data felt to be unusable

  The remainder of this presentation discusses the challenges we encountered…

Motion Artifact   To maintain anatomical distances/depths,

specimens were not compressed during image acquisition

  Specimen prone to minor motion as the machine moved through the range of angles

•  blurring of lesion margins and fine calcifications

•  blurring of the in-plane specimen margin

  Specimen secured with plastic wrap which was then taped to the imaging surface variable amount of motion artifact Hover mouse over image

to Play

Wire Echo Artifact   Extensive echo artifact relating to

the localization wire

  Arc/fan shaped distribution in a single plane, over multiple slices

  Related to image acquisition over multiple angles +/- motion artifact

  Limited assessment by obscuring adjacent small lesions / calcifications in that plane

Hover mouse over image to Play

Specimen Radiograph vs. DT

Specimen Radiograph No motion artifact

DT image Wire echo artifact and image blur

2a  

2b   Specimen Radiograph

No motion artifact DT image (in plane of wire) No significant motion artifact

Wire Echo Artifact

Potential solutions to minimize this artifact:

•  Manipulating the reconstruction algorithm may help suppress/minimize this artifact o  However, this may also affect the appearance of the lesions within the

specimen

•  Replacing localization wires with radioactive seeds

Delineating margins   DT measures x-ray transmission through

tissue over a range of angles series of images reconstructed for different heights above detector (z-axis)

  The true margin in a particular imaging plane should produce a sharper margin •  However, in many cases it was difficult to

delineate the true margin in that specific plane from the margin of an adjacent plane

  Each image includes tissue at the height of focal plane and overlapping tissue •  This factor + multilobulated margins of

specimens + motion artifact appearance of multiple possible margins

Well-visualized cancer with minimal motion or wire echo artifact.

Can you define the margins of the specimen on each plane?

Hover mouse over image to Play

Posterior Margin Visualization

  Posterior-most aspect of specimen (directly on the specimen plate) incompletely included on the reconstructed images •  improved by raising the specimen on a clear plastic block

Directly on imaging plate Raised on block

Note extensive motion artifact and wire echo artifact on both sets of images

Hover mouse over images to play clips

(Cine: Posterior Anterior)

Additional Considerations

  Artifact inherent to the tomosynthesis equipment: •  Degree of background noise inherent to the

tomosynthesis unit may vary between vendors

•  All specimens were imaged using the same machine

•  Images acquired using step-and-shoot method

•  Trial using other units/vendors may be considered

Conclusion   While the concept of multiplanar specimen margin analysis

with DT has potential, the multiple challenges and artifacts encountered in this preliminary study limit its practical application, at least in its current state.

  Future work on minimizing the technical issues may help improve the quality of the images, potentially making it more feasible and applicable to general practice. •  Ideas to explore…

o  Adding reconstruction algorithms to suppress artifacts such as the wire echo artifact

o  Using radioactive seeds for localization instead of wires

o  Trial of continuous tube motion during x-ray exposure vs. the step- and- shoot method used in this study