MEDIC ARFI in BREAST TUMORS

CLINICAL FINDINGS of ARFI in BREAST TUMORS

VO NGUYEN THUC QUYEN, PHAN THANH HAI, MEDIC MEDICAL CENTER,

HCMC, VIETNAM

INTRODUCTION:

Breast Cancer is currently the top cancer among women worldwide including Viet nam. Therefore, early detection plays a critical role in clinical decision of management.

Besides Mammography and MRI, ultrasound has been a useful modality in detecting breast tumors. Moreover, the combination with Color Doppler significantly reinforces the B-mode diagnosis. Lately, new ultrasound technique, elastography is providing more information to increase accuracy. However, each one uses different method including compressed and non-compressed technologies. Developing by Siemen, ARFI is a non-compressed elastography, evaluates tissue stiffness base on replacement caused by acoustic radiation force impulse (ARFI). In other words, tissue deformed and reformed  under a force. The stifferness replaces less compared with surrounding tissue in same depth. In clinical application, tumors usually harder than healthy tissue.

AIMS:

To evaluate ARFI qualitative and quantitative assessment to differentiate benign and malignant breast tumors.

METHODS and MATERIALS

Patient and Pathologic diagnosis:

From April to November 2015, we selected 85 breast lesions classified as category 3-5 according to ACR Breast Imaging Recording and Data System (BI-RADS). Two radiologists analyzed them in the following steps before performed biopsy with final diagnosis (FNAC, Core Biopsy, Excisional Biopsy). All images and biopsy procedures were performed at Medic Medical Center Ho Chi Minh city. Exclusion criteria include:

·         Non histopathology confirmation

·         Male breast lesions

Imaging methods:

Using linear probe 9L4 (9MHz) in Siemens Acuson S2000, we applied respectively 2 modes:

·         VTI (Virtual Touch Quantification): an gray-scale elasticity map within region of interest (ROI)

·         VTQ: (Virtual Touch Quantification): quantitatively measure shear-wave speed (m/s) within non-resizable ROI. The ROI was set in multiple point of the lesion to get the mean measurement.

Step 1: scan B-mode and Color Doppler images, classified lesion using BI-RADS lexicon (shape, orientation, border, echotexture, posterior feature)

 Step 2: Acquired Elasticity Score (E.S) in VTI mode then measure Area Ratio (proportion between VTI lesion area and B-mode area). Base on VTI map, we classified lesions with 5 elasticity score: Figure

            Score 1: totally white

            Score 2: mosaic (mix multi-shade of grey and white)

            Score 3: black core with white or grey or mix

            Score 4: totally or near to complete black

            Score 5: totally black with black component out of lesion

Score1-3: low suspect of malignancy

Score 4-5: high suspect of malignancy

Step 3: Set ROI in 5 different points of the lesion then measured Shear-wave Velocity (SWV) in VTQ mode. We calculated mean velocity for each lesion. The ROI in VTQ mode are fixed with 5 x 5 mm in size. When acquired velocity reach over 9.10m/s or computer is unable to get the signal, we have X.XX m/s as value. [1] Figure 2.

Figure 2: Shearwave travels through hard tissue very fast with > 9.10m/s (X.XX m/s value)

Statistic analysis:

We use SPSS version 16.0 to identified cut-off value and obtain ROC for best value of sensitivity and specificity. Once we get cut-off value, we use t-student analysis to see whether benign and malignant populations were statistically different.

           

RESULT

This study was approved by the institutional review board and informed consent was obtained from all participants. From April to November 2015, we selected 85 breast lesions including 59 benign (69.4%) and 26 (30.6%) malignant. Lesions appear to dominantly locate in right breast 52/85 (61.2%), left 33/85 (38.8%). The mean size 16.26 ±6.56 width and  9.64 ±5.01 mm depth

Histopathologic diagnosis	n (%)
Malignant:  Invasive ductal carcinoma	26 (29.4)
Benign	59 (70.6)
Fibroadenoma	5 (5.9)
Mastitis	3 (3.5)
Intraductal papilloma	2 (2.4)
Fibrocystic change	46 (55.3)
Others	3 (3.5)
Total	85 (100)

Table 1: histopathlogic diagnosis of malignant and benign breast lesions

ARFI analysis

-VTI:

a/ Elasticity Score (E.S)

	Malignant (%)	Benign (%)
ES 1	0	0
ES 2	0	52.5
ES 3	0	47.5
ES 4	23.1	0
ES 5	76.9	0
Total	100	100

Table 2.1: ES Score frequency of malignant and benign lesion

As the table 2.1, 26/26 cancer cases has ES 4-5 within suspicious range.

b/ Area ratio (A.R)

Area Ratio	Sensitivity (%)	Specificity (%)
1.06	100	27.2
1.13	96.2	52.5
1.20	88.5	64.4
1.34	88.5	94.9
1.40	84.6	96.6
1.44	84.6	98.3

Table 2.2:

As the table 2.2, the AR cut-off point would best at 1.34 with sensitivity 88.5% and specificity 94.9%. Area under ROC curve for malignancy is 0.933.

-VTQ:

We excluded 8 malignant cases has SWV as X.XX m/s

SWV	Sensitivity (%)	Specificity (%)
2.20	100	69.5
2.24	94.4	72.9
2.32	88.9	79.7
2.41	83.3	83.1
2.49	77.8	88.1

Table 2.3:

As the table 2.3, the SWV cut-off point would best at 2.24 with sensitivity 94.4% and specificity 72.9%. Area under ROC curve for malignancy is 0.911.

DISCUSSION

The ability of early detection

ARFI helps in differentiate malignant and benign lesion. E.S score in VTI mode suggest suspicion are quite accurate in this study (26/26). The gray-scale map not only distinguish big tumors but also in small tumors as case demonstrated (Figure 3). It could greatly aid in early detection.

Figure 3: A DCIS 6 x 5 mm mass with BI-RADS 5 in B-mode and ES 5, infiltration is clearly demonstrated which is not visible on conventional B-mode.

In term of quantitative evaluation, Area Ratio reinforced E.S. It also shows a better the cancerous infiltration in surrounding tissue than conventional method. In conventional ultrasound, only when halo rings, architecture distortion, skin changes suggest infiltration. However, those present in late stage while we are aiming for early detection. (Figure 4)

Firgure 4: non-halo tumors with AR=1.81 is better demonstrated the surrounding invasion

Our cut-off value

Our SWV cut-off point at 2.24 m/are suitable for clinical practice. Other reference studies were significantly higher (Yoon Seok Kim et al: 4.23±1.09 m/sec [2]) as they considered all X.XX value as 9.10m/s. We excluded all X.XX value since it not actually equals 9.10m/s.

Role in clinical diagnosis

In clinical application, ARFI increases the accuracy of B-mode and Color Doppler. It most value in BI-RADS 3-4a lesion which are the borderline between benignity and malignancy. We recommended grade up from BI-RADS 3 to 4A if all ARFI features are suspicious. However, here are some exceptions. Acknowledged that some cancer such as Inflammatory Breast Cancer (IBC) tends to be softer than normal tissue, reversely, some benign condition like Mastitis can mask malignancy (figure 5). Our study limited in 85 case and not included any IBC however caution should be made if specially AR> 1.34. An interesting study was held by M.Teke et al. which used ARFI to compare Idiopathic Granulomatous Mastitis with Breast Cancer . Study shown significantly different between their SWV (cut-off value 4.08m/s with 80.6% sensitivity, 86.4% specificity). It is important not to miss cancer but still minimalize invasive option. EFSUMB also recommend this concept but less certain in down grade. In some situation, we can down grade 4A lesion if the technique done right, such as circumscribed lesion with suspicious Doppler pattern or posterior feature. ARFI also helps guiding FNA procedure as we puncture the hardest points in the lesion on VTI map.  

Figure 5: Mastitis lesion in 60 years old patient, BI-RADS 4C E.S 2, AR=1.1 and VTQ=1.58m/s

Technical recommendation

CONCLUSION

Overall, ARFI is a useful tools for diagnosis and biopsy guidance breast tumors. The technique is simple since it is non-compressed and repeatable. It cannot replaced biopsy but reinforced conventional ultrasound. This is a promising technique helps avoiding invasive diagnosis if we use it right and well-combined with other features.

REFERENCES:

1/ Wojcinski S, Brandhorst K, Sadigh G, Hillemanns P, Degenhardt F. Acoustic radiation force impulse imaging with Virtual Touch^TM tissue quantification: mean shear wave velocity of malignant and benign breast masses. International Journal of Women’s Health. 2013;5:619-627. doi:10.2147/IJWH.S50953.

2/ Kim YS, Park JG, Kim BS, Lee CH, Ryu DW. Diagnostic Value of Elastography Using Acoustic Radiation Force Impulse Imaging and Strain Ratio for Breast Tumors. Journal of Breast Cancer. 2014;17(1):76-82. doi:10.4048/jbc.2014.17.1.76.

3/ M. Teke, M. Gümüş, F. Teke. Combination of elastography and tissue quantification using the acoustic radiation force impulse technology for differential diagnosis of Idiopathic Granulomatous Mastitis with Breast Cancer. ECR 2015 http://dx.doi.org/10.1594/ecr2015/C-1835

4/D. Cosgrove¹, F. Piscaglia², J. Bamber³. EFSUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography.Part 2: Clinical Applications. Ultraschall in Med 2013 DOI: 10.1055/s-0033-1335375

ULTRASOUND ANATOMY INCREASES UNDERSTANDING of LIVING ANATOMY

Abstract

Despite increase in residency programs including ultrasound training, few medical schools have incorporated it into their curricula. The Gross Anatomy course at Mayo Medical School has introduced ultrasound in the curriculum. Cadaver dissection teaches students static anatomical relationships, but ultrasound offers dynamic display of how those relationships can change with movement. Ultrasound curriculum consists of four 1 hour didactic sessions and five 30 minute hands-on modules, covering Carpal tunnel, Heart, Abdominal viscera, and Doppler imaging of blood flow. Each module is guided by a checklist of techniques and structures. Students are graded using ARS system, and ultrasound objectives are incorporated into the final exam. This study aimed to assess effectiveness of ultrasound curriculum in a 7 week anatomy course. Students were asked to complete pre- and post- test surveys that assessed whether ultrasound sessions allowed them to better appreciate living anatomy, learn the basics of operating a portable ultrasound machine, and become more comfortable with medical technology. Pre and post surveys showed that ultrasound helped students appreciate living anatomy, and that they were comfortable with technology. There was an increase in students’ perception of their ability to interpret ultrasound images with a p-value of 0.000026. Ultrasound was a successful addition to the anatomy curriculum.

MEDIC CHUẨN BỊ THAM DỰ AFSUMB 2016

1/ ARFI of TESTIS at MEDIC CENTER, NGUYEN THIEN HUNG - LE VAN TAI - PHAN THANH HAI, MEDIC MEDICAL CENTER, HCMC, VIETNAM

PURPOSE:

Acoustic radiation force impulse imaging (ARFI) is a new technique for the sonographic quantification of tissue elasticity. We applied  ARFI elastography to investigate the stiffness of  the normal and pathologic testes.

METHOD and MATERIALS:

20 male volunteers underwent normal B-mode sonography with ARFI elastometry of both testes using a Siemens Acuson S2000™ (Siemens Healthcare, Germany) system. 12 cases of testicular tumor  and 03 cases of hematoma were encountered in our study.  Results were statistically evaluated.

RESULTS:

-          From 40 normal testes of 20 male individuals, mean elastic velocity VTQ= 0.87+/- 0.11m/s [range 0.72-1.12 m/s]

-          From 03 cases of hematoma, mean elastic velocity VTQ=1.39+/-0.02m/s.

-          From 12 cases of testicular tumor, mean elastic velocity VTQ= 1.51+/- 0.18 m/s (range 1.26-1.69m/s) with the meaning more stiffness than normal and hematoma testis. On VTI tumor are harder the parenchyma (black color or blue code)

CONCLUSION:

ARFI elastometry  provides the initial values of testicular stiffness in normal and pathologic status. Further studies with more subjects may be required to define the normal range of values for normal and pathologic groups.

2/ARFI for OBSTRUCTIVE and with UPJO HYDRONEPHROSIS in ALDULT

NGUYEN THIEN HUNG - TRAN NGAN CHAU- PHAN THANH HAI, MEDIC MEDICAL CENTER, HCMC, VIETNAM

ABSTRACT:

We applied ARFI technique from Siemens S2000 to evaluate whether fibrotic process existing in adult hydronephrosis.

Using 1-4 MHz convex probe we calculated in 3 positions of hydronephotic kidney due to  obstruction [stone, outside compression] (n=33 cases), due to ureteropelvic junction obstruction [UPJO] (n=30 cases]. We had a control group of normal kidney (n=36 cases). Mean value of ARFI velocity of obstruction hydronephrosis (due to stone) was 2.73+/-0.39m/s and of UPJO hydronephrosis was 1.66+/-0.16m/s while in control group was 1.6+/-0.2m/s. There were stastistic differences of 2 stone and UPJO hydronephrosis groups (p < 0.0001), with stone hydronephrosis and control (p < 0.0001). But no statistic difference exists in UPJO hydronephrosis and control group.

3/ CLINICAL APPLICATION of Acoustic Radiation Force  Impulse  in BREAST TUMOR at MEDIC CENTER, PHAN THANH HAI PHUONG, VO NGUYEN THUC QUYEN, PHAN THANH HAI

INTRODUCTION

Early detection of Breast Cancer plays a critical role in decision making. Besides mammography and MRI, ultrasound has been a useful modality in detecting breast tumors. Moreover, the combination with Color Mode significantly reinforces the B-mode diagnosis. Lately, new ultrasound technique, elastography is providing extra information to increase accuracy. However, each one uses different method including compressed and non-compressed technologies. Developing by Siemens, ARFI is a non-compressed elastography, evaluates tissue stiffness base on replacement caused by acoustic radiation force impulse (ARFI).

AIMS:

To evaluate ARFI qualitative and quantitative assessment to differentiate benign and malignant breast tumors.

METHODS and MATERIALS

From April to November 2015, we selected 85 breast lesions classified as category 3-5 according to ACR Breast Imaging Recording and Data System (BI-RADS). Two radiologists analyzed them in ARFI features : Elasticity Score (E.S) which on scales 1-5 (Score 1-3: low suspicion, Score 4-5: high suspect of malignancy), then measure Area Ratio (proportion between VTI lesion area and B-mode area) and set ROI in 5 different points of the lesion then measured Shear-wave Velocity (SWV). Biopsy were required for final diagnosis (FNAC, Core Biopsy, Excisional Biopsy). Exclusion criteria include: Non histopathology confirmation or Male breast lesion.  

RESULT

85 selected breast lesions includes 59 benign (69.4%) and 26 (30.6%) malignant. Lesions appear to dominantly locate in right breast 52/85 (61.2%), left 33/85 (38.8%). The mean size is 16.26 ±6.56 transversely and perpendicularly 9.64 ±5.01 mm. In ES assessment, 26/26 cancer cases were within suspicious range ( ES4-5). The AR cut-off point would best at 1.34 with sensitivity 88.5% and specificity 94.9% (area under ROC curve for malignancy is 0.933). After excluded 8 malignant cases has SWV as X.XX m/s, the best SWV cut-off point is at 2.24 with sensitivity 94.4% and specificity 72.9% (area under ROC curve for malignancy is 0.911).

CONCLUSION

Overall, ARFI is a useful tools for diagnosis and decision of biopsy breast tumors. The technique is simple since it is non-compressed and repeatable. It cannot replaced biopsy but reinforced the Conventional ultrasound  findings. This is a promising technique helps avoiding invasive diagnosis if we use it right and well-combined with other features. 

4/ Ultrasound findings of rib fractures in undetected cases by chest x-rays
Le Thanh Liem MD, Phan Thanh Hai MD
Medic Medical Center, Ho Chi Minh City, Vietnam
Abstract:

OBJECTIVE:

To accumulate experiences of detection of costal cartilage and rib fractures which are negative on X-ray films of  chest trauma patients.

METHODS:

A total of 112 patients at the Medic Medical Center from 2008 to 2015, suffering from chest trauma, detected costal cartilage or rib fractures on chest ultrasound with a 7.5 MHz linear transducer of ultrasound. All patients were examined later by chest X-ray. Statistical analysis was done to outline the ultrasound findings of these rib fractures.

RESULTS:

In 112 patients showed costal cartilage and anterior rib lesions, only 10 patients (9%) showed of rib fracture on chest X-ray film, whereas 102 other patients (91.0%) had no evidence of rib lesions on chest X-ray film. Fracture of the rib with a disruption of continuity of bony cortex, mostly located near the costo-chondral junction. Rib fracture cases that the displacement is minimal, usually detected by longitudinal plane based on accompanied by the soft tissue edema or hematoma around the fracture site. Costal cartilage fractures were in five patients (4,5%). Costal cartilage fracture appeared as disruption of cortex, small echogenic lines in cartilage, and bruised cartilage. In addition to detecting rib fractures, ultrasound helps evaluating the stage of disease based on the presence of hematoma, cartilage callus or bone callus. Some patients may not specify the position localized pain or may not remember history of trauma until there is evidence of ultrasound to confirm the diagnosis.

CONCLUSIONS:

Ultrasonography is a useful imaging modalities in disclosing the rib fractures which were negative on chest X-ray film in chest trauma.

Although no significant change in treatment, but the detection of rib fractures is very helpful in explaining the cause of pain, reducing the anxiety of patients and avoid other unnecessary diagnostic procedures.

HEPATITIS B: 50 years after the discovery of Australia Antigen

Ultrasound guidance lowers mastectomy risks

US guidance lowers mastectomy risks

60 YEARS of DOPPLER ULTRASOUND in MEDICINE

Shear-wave elastography aids monitoring of tendinopathy

Shear-wave elastography aids monitoring of tendinopathy

By Erik L. Ridley, AuntMinnie staff writer

 Shear-wave elastography performs better than B-mode and power Doppler ultrasound for evaluating tendinopathy and helping to assess treatment response, German researchers recently reported at the RSNA 2015 meeting in Chicago. Click here to learn more.

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Ultrasonography Fundamentals In Critical Care: Lung Ultrasound,

http://www.slideshare.net/basselericsoussi/ultrasonography-fundamentals-in-critical-care-lung-ultrasound-pleural-ultrasound-other-potetial-utilities-of-ultrasound

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http://www.criticalecho.com/content/tutorial-9-lung-ultrasound

HOW I DO IT : LUNG US

http://www.medscape.com/viewarticle/830111

SWE and TENDINOPATHY

Shear-wave elastography aids monitoring of tendinopathy

By Erik L. Ridley, AuntMinnie staff writer

December 15, 2015 -- Shear-wave elastography performs better than B-mode and power Doppler ultrasound for evaluating tendinopathy and helping to assess treatment response, German researchers recently reported at the RSNA 2015 meeting in Chicago.

Not only was shear-wave elastography more sensitive for detecting tendinopathy in a prospective study, but the technique's quantitative data had much higher correlation with clinical examination scores, according to presenter Dr. Timm Dirrichs of University Hospital RWTH Aachen in Aachen, Germany

LIVER ELASTOGRAPHY IN THE PREDICTION OF THE PRESENCE OF HCC

LIVER ELASTOGRAPHY IN THE PREDICTION OF THE PRESENCE OF HCC

Prognosis of patients with chronic liver disease is determined by the extent and progression of liver fibrosis, which may lead to the development of HCC. Liver stiffness is significantly higher in patients with HCC than in patients without HCC. However, most of the studies found that liver stiffness alone is insufficient to predict the presence or absence of HCC and that it should be associated in a score with other markers. A score developed by Wong et al based on liver stiffness, age, serum albumin and hepatitis B virus DNA level was found to have AUROC’s of 0.83 to 0.89 in the identification of the HCC patients and a very good negative (99.4%-100%) for the exclusion of HCC in patients. In the study conducted by Feier et al, LS was significantly higher (42 kPa vs 27 kPa, P < 0.0001) in the HCC group than in the non-HCC group, but other 3 parameters (alanine-aminotransferase, alphafetoprotein and interquartile range of the LSMs) were added to elastography in a score and the resulted model combining the four variables showed a good diagnostic performance in both training and validation groups, with AUROCs of 0.86 and 0.8, respectively. Jung et al has shown that liver stiffness is also useful as a part of a predictive model that identifies patients that are at risk for late recurrence after curative resection of HCC. On multivariate analysis, patients with older age, male sex, heavy alcohol consumption (> 80 g/d), lower serum albumin, HBe antigen positivity and LSM> 8 kPa were at a significantly greater risk of HCC development.

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SMI on Toshiba Aplio 500

Superb Micro-Vascular Imaging (SMI) is an innovative ultrasound Doppler technique developed by Toshiba. SMI offers a unique algorithm that allows visualization of microvasculature with low velocity but without using any contrast agents.

 The advantages of SMI include 
 1) low velocity flow visualization, 
 2) high resolution 
 3) minimal motion artefact, and
 4) high frame rates. The exceptional vessel detection ability allows SMI to be of benefit in the evaluation and treatment of liver diseases. 

SMI has potential in:
 i. Display of minute intra-lesional vasculature
 ii. Evaluating RFA treatment
 iii. Support RFA planning and guiding.

Advanced Applications

Superb Micro-Vascular Imaging (SMI)*

Toshiba's innovative Superb Micro-Vascular Imaging (SMI) technology expands the range of visible blood flow and provides visualization of low velocity microvascular flow never before seen with ultrasound. SMI's level of vascular visualization, combined with high frame rates, advances diagnostic confidence when evaluating lesions, cysts and tumors, improving patient outcomes and experience. Improve Accuracy and Speed with SMI Getting accurate diagnostic information faster is just one reason why Toshiba’s Superb Micro-Vascular Imaging (SMI) is an integral part of operations for our partners at Rex Healthcare.

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ELASTO + B-MODE US for BREAST CANCER

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ANKYLOSING SPONDILITIS and ULTRASOUND

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Ultrasound shows thyroid cancer spike after Fukushima

By Erik L. Ridley, AuntMinnie staff writer

October 14, 2015 -- Just as many had feared, the disaster at the Fukushima Daiichi nuclear power plant in March 2011 has sparked a sharp increase in thyroid cancer among children and adolescents in the area, according to a study published online in Epidemiology. And more cases may be lurking.

One particularly hard-hit district in the Fukushima Prefecture saw thyroid cancer rates that were 50 times higher than the national average in Japan among those 18 and younger, reported researchers who participated in a thyroid ultrasound screening program in the three years after the earthquake. Cancer rates throughout the prefecture are 30 times higher than in Japan as a whole.

"The result was unlikely to be fully explained by the screening effect," wrote the research team led by Dr. Toshihide Tsuda, PhD, of Okayama University. "In Chernobyl, excesses of thyroid cancer became more remarkable four or five years after the accident in Belarus and Ukraine, so the observed excess alerts us to prepare for more potential cases within a few years."

Radiation exposure

Following the meltdown of three Fukushima nuclear reactors, approximately 900 petabecquerel of radiation was released into the atmosphere, the radiological equivalent of one-sixth of the 5,200 petabecquerel released by the Chernobyl disaster. Based on its preliminary dose estimation in 2012, the World Health Organization (WHO) predicted there would be an increase in thyroid cancers among children who had been exposed to the radiation.

WHO estimated that those in the most affected areas of the prefecture received thyroid-equivalent doses of 100-200 mSv, while those in the rest of the prefecture received 10-100 mSv via inhalation, ingestion, and external exposure from fallout deposits on the ground, according to the researchers (Epidemiology, October 5).

Nearly four years after the accident, the group sought to determine accurate and quantitative estimates from the Fukushima experience to plan for the population's future health needs.

Thyroid ultrasound screening

Under a screening program planned and conducted by the government of the Fukushima Prefecture, all residents 18 years or younger received thyroid ultrasound screening sometime during the 2011-2013 fiscal years. Screening was performed in three areas: in 2011 in the area nearest the disaster, mostly within 50 km of the Fukushima plant; in 2012 in a middle area of the prefecture; and in 2013 in the least-contaminated area.

A second round of screening, which will also include residents born in the prefecture between April 2, 2011, and April 1, 2012, began in April 2014 and is expected to be completed in March 2016.

Those with positive ultrasound findings on screening received a secondary exam, followed by fine needle aspiration (FNA) biopsy if necessary. Patients with detected cancer cells were followed and operated on at an appropriate time, according to the researchers.

Of the 367,687 residents 18 years or younger in the prefecture in 2011, 298,577 (81%) had received the first round of screening by the end of December 2014. There were 2,251 positive thyroid ultrasound cases by 2014 and 2,067 received a secondary exam.

From these, FNA indicated the presence of 110 thyroid cancers, 87 of which had been operated on by the end of 2014. On histological examination, 86 were confirmed to be malignant, a number that included 83 papillary carcinomas and three poorly differentiated carcinomas.

The researchers compared the prevalence of thyroid cancer for each area by calculating a prevalence odds ratio in comparison with the least-contaminated district of the least-contaminated area of the prefecture. For a comparison with subjects outside of the prefecture, the team calculated incidence rate ratios in comparison with annual incidence rates nationwide in Japan, taking into account the prevalence as well as the latent duration (four years) of the disease.

Thyroid cancer prevalence
Area	Prevalence of thyroid cancer per 1 million people	Prevalence odds ratio compared to least-contaminated district	Incidence odds ratio compared to Japan national rates
Nearest to Fukushima	359	1.5	30
Middle -- not evacuated	402	1.7	33
Least contaminated	332	N/A	28

The researchers noted that the highest incidence odds ratio (50; 95% confidence interval: 25-90) in comparison with the mean Japanese annual incidence of thyroid cancer was found in the middle area's central middle district -- 50 to 60 km west of the power plant -- where residents were not evacuated. That district had a prevalence rate of 605/1,000,000 (95% confidence interval: 302-1,082) and a prevalence odds ratio in comparison with the least-contaminated district of 2.6 (95% confidence interval: 0.99-7.0).

The finding that southernmost districts within the middle and the least-contaminated areas of the prefecture had higher incidence rates than the northernmost districts was consistent with the flow of indium-131 being primarily in a southern direction from the Fukushima release.

2nd round of screening

In the second screening round that began in 2014, 106,068 (49%) of 218,397 total subjects have been screened so far. Of the 71% of exams with a decision as to whether the secondary exam was necessary or not, there were 611 positive studies.

The secondary exam has been performed on 377 subjects (62% of the positive studies), and 262 received a final diagnosis on the secondary exam. FNA was performed on 22 subjects (8%) and detected eight new thyroid cancer cases by cytology as of December 31, 2014. All eight had negative ultrasound findings in their first round of screening.

New data released in May 2015 added two additional thyroid cancer cases from the first round of screening and seven more cases from the second round (for a total of 15). As a result, the incidence ratio so far from the second round of screening is 13.7 (95% confidence interval: 7.7-23).

The authors concluded that within as few as four years after the disaster, there has been an approximately 30-fold increase in thyroid cancer among children and adolescents in the Fukushima Prefecture. As the number of thyroid cancer cases has increased faster than predicted by the WHO, it's possible that the organization's previous exposure estimates for residents were too low, according to the group.

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