role of tomosynthesis in assessing the size of the breast lesion

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Role of Tomosynthesis in Assessing the Size of the Breast Lesion

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Role of Tomosynthesis in Assessing the Size of the Breast Lesion

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Role of Tomosynthesis in assessing the size of the breastlesion

Poster No.: C-1045

Congress: ECR 2012

Type: Scientific Exhibit

Authors: B. Raghavan1, M. Selvakumar2; 1CHENNAI, TA/IN, 2Chennai/IN

Keywords: Pathology, Outcomes analysis, Ultrasound, Mammography, Breast

DOI: 10.1594/ecr2012/C-1045

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Purpose

To assess the role of 3D tomosynthesis in the evaluation of the size of malignant breastlesions and to compare it with the size in 2D, Ultrasound and final Histopatholgy.

This is a preliminary study to investigate the ability of 3D Tomosynthesis in assessing thepre-operative size of malignant breast lesions in comparison to 2D digital mammogramand sonographic imaging modalities, and in predicting the gold standard, pathologicaltumor size.Tumor size obtained by pathology which remains the gold standard has been comparedby many authors with X-ray mammography, Ultrasound and MR mammography. Manystudies have shown that X-ray mammogram is better than breast Ultrasound in predictingthe size of the lesion though ultrasound is faster, less expensive and widely available.MRI appears to measure the lesion size slightly better than X-ray mammogram becauseof the 3D presentation of a lesion when compared to other modalities, but remains acostly investigation and is done less often than X-ray mammogram.Accurate measurement of a primary invasive breast cancer is crucial for stagingand patient management, in particular with the increased use of breast-saving andreconstructive surgery. Neo-adjuvant chemotherapy is now commonly employed basedon the pretreatment imaging size and the size assessment is also important in evaluatingresidual tumor extent after preoperative treatment with cytostatic drugs. Hence it isimportant to document the size of the lesion in order to categorize it in the appropriatelocal staging to decide on the mode of therapy and also for follow-up .

3 D Tomosynthesis combined with 2D FFD mammograms in the combined mode is arelatively new technique which offers better delineation of margin. Margin analysis of alesion forms the very basis of measuring the size of the lesions. 3D sectional analysis canovercome the problems due to superimposition of tissues especially in dense breasts.

Methods and Materials

Our study was a retrospective study, collecting and examining data already held inpatient's files. The patients' consent was obtained initially at screening. The data wascollected between May and November 2011 and processed.

About 100 abnormal imaging studies by Diagnostic Full field Digital mammogram (Comboview for 2D and 3D studies were done for all cases) and breast Ultrasound were reviewed.From these , 62 patients who had malignancy proved by Tru-cut biopsy were included inthe study. These patients had been advised treatment based on these results. Of these,

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few were lost to follow-up and few had palliative chemotherapy.Such patients were notincluded in the study.

The maximum size of the tumor in 47 patients was analysed in two views by 3Dtomosynthesis and compared to the size in tfinal HPE. Comparison of the tumor size inUS and 2D was also done.All patients in our study had undergone Combo view Diagnostic Full field Digitalmammogram that includes 2D mammogram and 3D tomosynthesis. The mammographicimaging protocol included cranio-caudal, medio-lateral oblique projections andmagnification projections, wherever required.

High-frequency grey-scale dedicated ultrasound examination of the breast wasperformed. The size of the lesion was measured with a high frequency probe rangingfrom7.3 Mhz to 13 MHz. When the size of the tumor was larger than the foot print of thetransducer lower frequency probe was used to get the edges of the mass within the frame.

MAMMOGRAPHIC MEASUREMENTS

All measurements were taken on the dedicated mammographic work-station withcallipers on the monitor. All magnification projections were excluded from themeasurement procedure.The process of mammographic measurement of tumors in our study was modeled onthe work of Flanagan et al [1] , based on the fact that the size excluding the spiculationscorrelated best with the post surgical measurement.For each mammographic lesion two measurements were recorded perpendicular to eachother. Spicules have been excluded from the measurements in stellate lesions and themeasurements were taken from the thickest point of the spicules on each side whichrepresented the nucleus of the tumor.[2]Out of the two, the longest measurement of each lesion was taken into consideration.Tumors were graded mammographically into nodular or stellate shape, and whether theywere found in fatty parenchyma or dense parenchyma.

SONOGRAPHIC MEASUREMENTS

The sonographic measurements were undertaken by measurement calipers incorporatedinto the ultrasound units. Measurements were taken in different ways depending on thegrowth pattern of the tumor and included:

1. From break to break in the tissue plane in diffuse masses where the tumordisrupts the natural breast architecture.

2. The hypo-echoic nucleus of the tumor in the case of circumscribed, nodulartype lesions.

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3. The largest diameter in stellate lesions which includes micro-lobulations andbranch patterns but excludes radiating hyper-echoic straight lines.

PATHOLOGIC MEASUREMENTS

Surgical pathology breast specimens were processed according to a standard protocol.Each breast excision or mastectomy specimen was serially sectioned and fixed informalin overnight. The tumor was then measured in three dimensions, to the nearestmillimeter, and submitted for microscopic evaluation.In general, the gross measurement of the tumor was used for staging.However, if the microscopic tumor measurement of the largest dimension wassubstantially greater than the largest gross measurement (eg due to microscopic tumorextension into surrounding tissues), or substantially smaller than the gross measurement(eg due to adjacent dense fibrocystic change), the microscopic measurement was utilizedfor staging. The largest diameter was used for depicting the HPE.

STATISTICAL ANALYSIS

Categorical data were presented by frequency with percentage and it was analyzedby using Chi-square and Fisher exact test. Karl Pearson's co-efficient of correlationwas used for relationship. Bland altman plot was used for measurement of eachmodalities and linear regression plot with 95% confidence interval was used to analyzethe performance of each modality in Fatty / Dense Breasts and Nodular/ Stellate lesion.All the analysis was done by using SPSS 14.0 version, A p value less than 0.05 wasconsidered as significant.

Images for this section:

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Fig. 1: 40years female presented with focal nodularity of the left breast. On combo view,the breast appears heterogenously dense(BIRADS 3)in nature and no measurable lesionwas detected in 2D mammogram. 3D tomosynthesis revealed a nodular lesion.

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Fig. 2: 45 years female patient presented with nodularity of left breast. on combo view,thebreast appears fatty (BIRADS 2).On 2D a stellate lesion was seen corresponding to thepalpable nodularity.3D tomosynthesis picked up an additional stellate lesion.

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Results

The maximum number of women in our study was between 40-50 years, (fig 3) and ageranged from less than 30 to more than 70 years.

Out of our 62 cases 12 cases were not measurable in 2D mammography (fig 4). 15 caseswho had undergone preoperative chemotherapy, radiotherapy or lost on follow up wereconsidered as histopathologically non measurable lesions (fig 4).

Only 8% of our tumor load was contributed by lobular carcinoma and 3% by malignantphylloides (fig 5).

Based on the BIRADS classification for breast tissue density 49% of our lesions (23 outof 47 lesions) were seen in fatty breasts (BIRADS 1,2) and 51% of our lesions(24 out of47 lesions) were seen in dense breasts (BIRADS 3,4) (fig 6). 62% of lesions were stellateand 38% of lesions were nodular in nature (fig 7).

Bland altman was used for the measurement of agreement between each modality. Theconfidence interval was high (0.858- 0.963) for 2D digital mammography in comparisonto 3D tomosynthesis (0.808- 0.952) and ultrasonography (0.585- 0.908) (Table 1, fig8-10). The 95% confidence index was high for 2D and 3D. It was lower for Ultrasound.In measurable lesions 2D performed better than 3D.

Table -1

Estimate 95% CI

2D 0.927 0.858- 0.963

3D 0.907 0.808- 0.952

USG 0.813 0.585- 0.908

With Linear regression plots, 2D and 3D mammography showed high prediction intervalfor lesions in fatty breast than in dense breast andin comparison with 2D mammography, 3D mammography had high prediction interval indense breast lesions .Both 2D and 3D showed high prediction interval for nodular lesions than stellate lesionsand 3D mammography was superior in predicting stellate lesions than nodular lesions incomparison to 2D mammography.

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Ultrasonography had better prediction index for nodular lesions ,especially in fatty breast .However it was not superior to 2D or 3D mammography. It had poor predictability in densebreasts and for stellate lesions.(Table2)

Table - 2

LINEAR REGRESSION ANALYSIS with 95% INDIVIDUAL PREDICTION INTERVAL-

(R2)

Fatty R2 Dense R2 Stellate R2 Nodular R2

2D .94 .74 .67 .93

3D .94 .75 .69 .91

US .87 .86 .43 .87

SIZE ESTIMATION:

Majority of our lesions were between 2-5 cms i.e local Stage 2 disease and we had veryfew less than 1 cms lesion (Fig 11).

All modalities under-estimated the size of the lesion with respect to HPE.HPE has alsobeen reported to under predict the tumor margin ,according to some studies , due totissue shrinkage of the surrounding parenchyma in formalin.

Table - 3

numbers mean in cms

Under measuring 21 .882D

Over measuring 11 .57

Under measuring 35 .713D

Over measuring 9 .59

Under measuring 33 1.15USG

Over measuring 11 .50

LIMITATIONSOur study being a preliminary study had less numbers and the entire range of malignantpathology could not be captured.

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Our study population is derived from opportunistic screening and is not population based.This gives us lesser cases in the stage1 disease and in early breast cancers less than 1cm where the performance of 3D Tomosynthesis is reported to be superior.

Images for this section:

Fig. 3: Age distribution

Fig. 4: Measurable and non measurable lesions

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Fig. 5: Histopathology distribution.

Fig. 6: Distribution of breast parenchymal density

Fig. 7: Distribution of morphology (nodular/stellate)of the lesion.

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Fig. 8: 2D-HPE consistency analysis

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Fig. 9: 3D-HPE consistency analysis

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Fig. 10: USG-HPE consistency analysis

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Fig. 11: Size and stagewise distribution of lesions

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Conclusion

Better predictability of sizes by Mammogram (2D and 3D) with respect to HPE was seenin our study (Table 1 and fig 8-10) and that correlates well with other studies also .

Cases in which the lesions are not measurable with 2D mammogram due tosuperimposition of dense glandular parenchyma, tomosynthesis proves to be the bettermodality for measurement (fig1 and 2), however if the lesion is measurable in 2D digitalmammography, it is superior to 3D tomosynthesis. This is probably because though 3Dtomosynthesis gives better margin characterization, each 1 mm section gives only partof the marginal information whereas 2D mammogram gives summated information of thelesion.

Ultrasound has a greater ability to demonstrate lesion characteristics when amammographic lesion is obscured by dense overlying tissue or if the lesion is onlyevident as a radiographic distortion. This is partly due to the ability of transducer tobe maneuvered through multiple planes to acquire multiple views and dimensions. Theresults of our study demonstrate that sonography was less useful than mammography inpredicting histological tumor size because most of our lesions were stellate in nature andare usually characterized by posterior acoustic shadowing on sonography, correspondingto associated desmoplasia in and around the lesion.The shadowing obscures theposterior border of the lesion, often making measurement in this longest diameter difficult.

Lobular cancer and associated DCIS are known to decrease the capability of imagingto predict size when compared to histopathology. In our study we found decreasedpredictablity by all modalities in 2 cases of lobular carcinoma which were T2 lesions and3D tomosynthesis predictablity was closest to HPE. However T1 lesions co-related wellwith HPE size in all 3 modalities.

Majority of the lesions were underpredicted with all the modalities. The averageunderestimate of breast tumor size with 2D and 3D mammography was 0.88 cm and0.71 cms respectively. The average underestimate produced by sonography was 1.15cm.Alternatively, over-estimation of breast tumor size by medical imaging may lead to amore radical approach at surgery. The average size of over estimation by 2D and 3Dmammography was 0.57 and 0.59cm respectively and 0.5 cm by sonography (Table 3).

CONCLUSION

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In this preliminary study 3D mammogram appears to be as reliable as 2D in predictingtumor size especially in stellate lesions and dense breast parenchyma , if it ismeasurable , whereas 2D is less reliable due to non-measurability, because of obscuredmargins and superimposition of tissues. However more numbers with significantdistribution patterns in size and pathological categorization needs to be done.

References

1. Flanagan FL, et al. Invasive breast cancer-mammographic measurement.Radiology 1996;3:819-23.

2. L.J. Dummin et al; Prediction of breast tumor size by mammography andsonography-A breast screen experience. j.breast.2006.04.003

3. Bobbi Pritt et al; Influence of breast cancer histology on the relationshipbetween ultrasound and pathology tumor size measurements. ModernPathology (2004) 17, 905-910

4. Tresserra F et al. Assessment of breast cancer size: sonographic andpathologic correlation. J Clinl Ultrasound 1999;27(9):485-91.

5. M. Kristoffersen Wiberg et al.Comparison of lesion size estimated bydynamic MR imaging, mammography and histopathology in breastneoplasms. Eur Radiol (2003) 13:1207-1212.

6. Fornvik, D, et al. Breast Tomosynthesis:Accuracy of tumor measurementcompared with digital mammography and ultrasonography. Acta Radiol 3;240-247, 2010.

7. Yeap BH et al. Specimen shrinkage and its influence on margin assessmentin breast cancer; Asian J Surg. 2007 Jul;30(3):183-7

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