Risk versus benefit in diagnostic radiology

The risks from the use of ionizing radiation in diagnostic radiology have been established, almost from the time at which X-rays were first discovered. The fundamental objectives of radiation protection are to avoid the occurrence of deterministic injuries and to minimize the risk of stochastic effects. The basic principles of radiation protection philosophy are justification and optimization. These principles are applied to ensure that diagnostic radiology procedures are safe. Implicit in the application of these principles is that the benefit/risk ratio is evaluated for all procedures. In practice, very little scientific work has been performed in this area, with the main exception of screening mammography. This article describes some of the problems in applying the justification principal in diagnostic radiology. An example calculation for screening mammography is given.     

Screening mammography: proven benefit,continued controversy

Screening mammography, despite its limitations, remains the best means for diagnosing breast cancer in asymptomatic women. Regarding the continuing controversies concerning the age at which screening should start, evidence supports beginning regular screening at age 40 in women at average risk . Similarly, evidence suggests that the screening interval should be yearly, especially in younger women. Rather than an arbitrary age at which screening should stop, the decision on screening elderly women should be made on an individual basis, taking into account level of health and life expectancy. More work needs to be done on determining the optimum screening strategies for high-risk women. As to the interpretation of screening mammography, a certain level of observer variability and of false-negative and false-positive readings are inherent in the process. These should be kept to a minimum through efforts by the interpreting radiologist to improve performance through auditing of individual results and continuing education. The impact of double reading and computer-aided detection in the interpretation of screening mammograms warrants further evaluation in terms of efficacy and cost-effectiveness. Despite these continuing controversies, mortality from breast cancer in the United States has been decreasing steadily for the past 25 years. The magnitude of the decrease has been reported to range from 8% to 25%. Although some of this decrease may be attributable to improvements in the treatment of breast cancer, early detection through screening mammography has undoubtedly played a role in this mortality reduction. The controversies that surround the issue of screening should not detract from the fact that screening mammography has proved to save lives.     

Observer variability in screen-film mammography versus full-field digital mammography with soft-copy reading

Full-field digital mammography (FFDM) with soft-copy reading is more complex than screen-film mammography (SFM) with hard-copy reading. The aim of this study was to compare inter- and intraobserver variability in SFM versus FFDM of paired mammograms from a breast cancer screening program. Six radiologists interpreted mammograms of 232 cases obtained with both techniques, including 46 cancers, 88 benign lesions, and 98 normals. Image interpretation included BI-RADS categories. A case consisted of standard two-view mammograms of one breast. Images were scored in two sessions separated by 5 weeks. Observer variability was substantial for SFM as well as for FFDM, but overall there was no significant difference between the observer variability at SFM and FFDM. Mean kappa values were lower, indicating less agreement, for microcalcifications compared with masses. The lower observer agreement for microcalcifications, and especially the low intraobserver concordance between the two imaging techniques for three readers, was noticeable. The level of observer agreement might be an indicator of radiologist performance and could confound studies designed to separate diagnostic differences between the two imaging techniques. The results of our study confirm the need for proper training for radiologists starting FFDM with soft-copy reading in breast cancer screening. Presented at ECR, Wien 2006.     

Light scanning versus mammography in breast cancer detection

Transillumination light scanning of the breast was compared with screen-film mammography in a prospective study of 1,110 women referred to an outpatient imaging department. Each method was interpreted independently of the other but with knowledge of physical examination findings. Of 24 biopsy-proved cancers, 14 (58%) were detected with light scanning and 21 (88%) with mammography. The 77 false-positive light scan examinations were attributed to technical factors and the inability of light scanning to distinguish malignant from benign conditions on the basis of imaging features. Of the ten false-negative light scan examinations, two were retrospectively reclassified as positive, but light scans in the other eight cases remained normal in appearance. The authors conclude that transillumination light scanning is not competitive with mammography as a screening method for breast cancer detection. furthermore, they were unable to identify a select subpopulation of women who might benefit from light scanning as an adjunct to mammography.     

两种数字乳腺X射线摄影系统的比较

目的探讨比较全视野数字乳腺X射线摄影系统(FFDM)与计算机乳腺X射线摄影系统(CRM)在影像质量与辐射剂量方面的差异。方法用FFDM对ALVIM乳腺摄影体模TRM进行自动曝光控制(AEC)摄影,再用CRM专用成像板(IP)在同一摄影机上用相同条件对体模摄影。固定AEC摄影时的kV值,选用曝光量数值14、16、18、22和24 mAs,在FFDM机上对模体摄影,记录上述摄影条件和入射皮肤剂量(ESD)及平均腺体剂量(AGD)。由5位影像科资深医师分别在相同条件下对所得影像进行软阅读,按照5分值判断法评判,然后绘制受试者工作特征曲线(ROC)曲线,计算出每种信号的判断概率值(P_det),对所得数据进行统计学分析。结果在辐射剂量均为1.36 mGy时,FFDM对模体内钙化点和肿块灶P_det值比CRM高,尤其是微小钙化点和小肿块灶,微小钙化点最大差值为0.215,小肿块灶最大差值为0.245。在相同的P_det值下,FFDM的辐射剂量比CRM低,ESD的值降低了26%,腺体平均剂量降低了41%。在使用FFDM摄影时,当mAs值超过AEC值时,P_det值没有明显改变。结论在相同曝光条件下,FFDM对乳腺钙化点和肿块灶的检出率高于CRM;在获得相似图像质量时,FFDM的辐射剂量明显低于CRM。     

Diagnostic accuracy of Fischer Senoscan Digital Mammography versus screen-film mammography in a diagnostic mammography population

RATIONALE AND OBJECTIVES: To compare the diagnostic accuracy of the Fischer Senoscan Digital Mammography System with that of standard screen-film mammography in a population of women presenting for screening or diagnostic mammography. MATERIALS AND METHODS: Enrollment of patients took place at six different breast-imaging centers between 1997 and 1999. A total of 247 cases were selected for inclusion in the final reader study. All known cancer cases were included (111) from all six participating sites representing 45% of the total cases. The remaining 136 cases (55%) were randomly selected from all available benign or negative cases from three of the six sites. A complete case consisted of both a (unilateral or bilateral) digital and screen-film mammogram of the same patient. Eight radiologists interpreted the cases in laser-printed digital and screen-film hardcopy formats. The study was designed to detect differences of 0.05 in the ROC area under the curve (AUC) between digital and screen-film radiologist interpretation performance. RESULTS: The average AUC for the Senoscan digital was 0.715 for the 8 readers. The average AUC for screen-film was 0.765. The difference AUC of -0.05 falls within the 95% confidence interval (-0.101, 0.002). The average sensitivity was 66% and specificity 67% for SenoScan full-field digital mammography. The average screen-film mammography sensitivity and specificity were 74% and 60%, respectively. CONCLUSION: No statistically significant difference in diagnostic accuracy between the Fischer Senoscan and screen-film mammography was detected in this study.     

Soft copy versus hard copy findings in digital mammography

The advantages of full field digital mammography are the excellent and reliable image quality and the reduction of radiation exposure. Image acquisition and display are decoupled in digital mammography allowing for optimization of both independently. Image displays are currently either hardcopy produced with a laser printer or softcopy using a computer monitor. Since the amount of data is high the hardware and software must meet specific technical specifications. The diagnostic accuracy of softcopy and hardcopy interpretation is comparable if a high resolution laser printer and a high quality workstation with high spatial and contrast resolution monitors are used. However, using film display the potential benefits of digital mammography in terms of manipulation of the data is lost. Additional diagnostic benefits might be gained by the combination of softcopy display and computer assisted diagnosis (CAD) and telemammography.     

Screening mammography. A risk versus risk decision

The potential risk of a radiologic procedure often is compared with the potential benefit of the procedure. While risk vs. benefit analysis has been useful as a step toward increased communication and understanding among radiologists, referring physicians, and the general public, it has the disadvantage that risk and benefit are fundamentally different quantities. Hence, their juxtaposition for purposes of comparison presents contextual difficulties. In this article, the concept is presented of comparing the risk of doing a procedure with the risk of choosing not to do the procedure. An example of risk vs. risk analysis of screening mammography for women over the age of 50 is given, with the conclusion that the risk of having yearly mammograms is less than 1/10 the risk of early death caused by failure to diagnose breast cancer by x-ray mammography. This approach to risk analysis would yield interesting data for examinations that are part of more complicated diagnostic pathways.     

Baseline screening mammography with one versus two views

Two-view baseline screening mammograms (oblique and cranial views) of 303 women recalled for further studies from among 7,245 women screened were reviewed by four experienced radiologists separately to evaluate the importance of the number of views taken for screening. As compared with the oblique view only, two views, increased the number of cancers detected and decreased the number of false-positive cancer diagnoses of two radiologists, but increased that of the other two.     

Breast biphasic compression versus standard monophasic compression in X-ray mammography

Breast biphasic compression (22.5 degrees angled paddle, followed by progressive angle reduction) was compared with standard monophasic compression in x-ray mammography. The presence of the pectoral muscle was recorded for the craniocaudal (CC) view and the presence of the inframammary fold for the mediolateral oblique (MLO) view. The amount of breast in each study and image quality were assessed for both views. For all parameters, biphasic compression performed better than monophasic compression in both CC (P: <.006) and MLO (P: <.04) views.     

Screen-film mammography versus xeromammography in the detection of breast cancer

There are two common methods of obtaining high-quality screening mammography: screen-film mammography (more simply, mammography) using a dedicated unit, and xeromammography. We studied the accuracy of the two techniques in detecting breast cancer by a retrospective study, analysing accuracy of interpretation in cases where both mammography and xeromammography were performed. Seventy-six patients were considered with 86 biopsies and mammograms resulting in detection of 32 cancers and 54 benign lesions. There was no difference in accuracy of interpretation between mammography and xeromammography. The sensitivities were: mammography 0.91, xeromammography 0.88. The specificities were: mammography 0.63, xeromammography 0.75. We conclude that both modalities are comparable in detecting cancer when optimal technique and experienced personnel are used.     

Low-dose intra-arterial streptokinase: benefit versus risk

Twenty-six unselected patients presenting with acute arterial ischaemia of a limb were treated with low-dose intra-arterial streptokinase under the joint care of a radiologist and a vascular surgeon. The results are reported and complications described. It is suggested that co-operative radiological and surgical management is essential and a shortened protocol for the safer administration of the drug is suggested.     

Risk factors for breast cancer in women undergoing mammography.

To determine risk factors for carcinoma of the breast, we compared women with cancer on screening and diagnostic mammography with those in whom cancer was not detected. For 39 months, medical histories were collected by mammography technologists on 3492 women having routine screenings or diagnostic mammograms at our institution. Potential risk factors of women with biopsy-proved breast cancer were compared with those in women who had normal findings on mammograms or negative biopsy results (control subjects). Of the 3492 women, 49 had biopsy-proved breast cancer. There were 3361 patients in the control group, including those women with normal findings on mammograms (3294) and those with negative biopsy results (67). Eighty-two women had incomplete questionnaires or were lost to follow up. Nearly all of the patients with breast cancer were postmenopausal compared with 68% of the control subjects. The mean length of lactation for breast cancer patients was significantly less than for control subjects: 5.6 vs 7.5 weeks (p = .015). This was true also for the postmenopausal patients: 8.1 vs 6.1 weeks (p = .041). Postmenopausal breast cancer patients had menstruated significantly more years (p = .016) than the postmenopausal control subjects: 34 vs 31 years, although the mean age at menarche was not different. When corrected for age, there was no significant difference in the total duration of menstruation in the postmenopausal cancer patients compared with the postmenopausal control subjects. Postmenopausal breast cancer patients had a significantly greater (p = .021) average body weight than postmenopausal control subjects: 71.7 vs 66.7 kg, although body weight was the same when all patients were considered. Similar results were found when Quetelet's index for obesity (weight in kg/height in cm2) (p = .004) was calculated for postmenopausal patients: 28 for cancer patients and 26 for control subjects. There was no significant difference in height between the cancer patients and control subjects when all patients or just the postmenopausal patients were considered. History of oral contraceptive use was significantly less common among postmenopausal breast cancer patients than among postmenopausal control subjects: 9% vs 20%. Patients with breast cancer had lower parity than the control subjects. In our series of patients, women in whom breast cancer was detected on mammography lactated less, showed no significant difference in years of menstruation when corrected for age, had a greater average body weight, used oral contraceptives less often, and had fewer children than women in whom no cancer was detected on mammography.     

Second-screening mammography: one versus two views per breast

To compare the advantages of one-view versus two-view second-screening (follow-up) mammography, oblique and craniocaudal projection mammograms from 1,000 consecutive asymptomatic women who had prior normal baseline studies were reviewed retrospectively, first with only the oblique images, then with the oblique and craniocaudal views. In women with dense breasts, one-view (oblique only) readings resulted in abnormal interpretations four times more frequently (53 cases, 5.3%) than two-view readings (13 cases, 1.3%). The induced cost from these abnormal interpretations would have more than offset the small savings in operating expense associated with one-view screening. In contrast, four times fewer abnormal one-view interpretations (13 cases, 1.3%) were made in women with primarily fatty breasts, in whom superimposition of dense tissue on images is not as frequently a problem. In these women, considering only cost, it may be reasonable to obtain a single mediolateral oblique projection for follow-up screening mammography. However, the issue of whether to implement such an approach remains unresolved, because the sensitivity of one-view versus two-view second screening in the detection of breast cancer has not yet been determined.