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First published online May 30, 2007
British Journal of Radiology (2007) 80, 508-515
© 2007 British Institute of Radiology
doi: 10.1259/bjr/17395663
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Full paper

FDG-PET/CT in restaging of patients with recurrent breast cancer: possible impact on staging and therapy

P Veit-Haibach, MD1, G Antoch, MD1, T Beyer, PhD2, H Stergar, MD2, R Schleucher, MD3, E A M Hauth, MD1 and A Bockisch, MD, PhD2

Departments of 1 Diagnostic and Interventional Radiology and Neuroradiology, 2 Nuclear Medicine and 3 Oncology, University Hospital Essen, Essen, Germany

Correspondence: Dr Patrick Veit-Haibach, Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstrasse 55, Essen 45122, Germany. E-mail: patrick.veit{at}uni-essen.de


   Abstract
Top
 Abstract
Introduction
 Methods and materials
 Results
 Discussion
 Conclusion
 References
 
We aimed to compare the value of combined positron emission tomography (PET)/CT, PET+CT (viewed side by side), CT alone and PET alone concerning the rTNM stage and influence on therapy in patients with recurrent breast cancer. 44 patients with suspicion of recurrent breast cancer underwent whole-body [18F]-2-fluoro-2-deoxy-D-glucose (FDG)-PET/CT. Images of combined PET/CT, PET+CT, PET alone and CT alone were evaluated by four blinded reader teams. Diagnostic accuracies and influence on therapy were compared. Histology and a mean clinical follow up of 456 days served as the standard of reference. Differences between the staging procedures were tested for statistical significance by McNemar's test. Overall TNM tumour stage was correctly determined in 40/44 patients with PET/CT, in 38/44 with PET+CT, in 36/44 with PET alone and in 36/44 patients with CT alone. No statistically significant difference was detected between all tested imaging modalities. PET/CT changed the therapy in two patients compared with PET+CT, in four patients compared with PET alone and in five patients compared with CT alone. Combined PET/CT appeared to be more accurate in assessing the rTNM and showed a moderate impact on therapy over PET and CT. Minor improvements were noted when compared with PET+CT. Experienced readers might therefore be able to provide accurate staging results for further therapy from separately acquired studies.


   Introduction
Top
 Abstract
 Introduction
Methods and materials
 Results
 Discussion
 Conclusion
 References
 
Breast cancer has a high prevalence among malignancies in woman in western countries [1, 2]. Imaging techniques play an important role in the detection and staging of breast cancer, because early detection improves patients' prognosis, and accurate staging has a substantial influence on therapy management (surgery, chemotherapy or radiation therapy) [3–5]. However, despite all of the improvements in diagnosis and treatment, the disease-free survival time remains relatively stable.

Follow-up examinations are made up to four times per year for the first 3 years, twice a year for the following 2 years and then annually in patients with adenomammectomy according to the European Society for Medical Oncology (ESMO) [6]. However, so far, worldwide agreement concerning the follow-up and therapy of breast cancer patients has not yet been achieved [6, 7].

Currently, depending on the patients' symptoms, follow-up of patients with breast cancer may involve a physical examination, the assessment of tumour markers, breast and axillary lymph node ultrasound, conventional mammography and magnetic resonance mammography (MRM) for local recurrence, CT and MRI for distant metastases and bone scintigraphy for osseous metastases.

Of these, based on their availability, CT and MRI are frequently used for cancer imaging when looking for organ or lymph node metastases [7, 9]. Both modalities may provide whole-body imaging if needed. The more widespread availability is an important advantage of CT but, unfortunately, CT is not applicable for local staging [10–13].

However, both modalities offer morphological data only. Limitations in lymph node staging based on morphological criteria have been well recognized [14, 15]. Apart from detecting distant metastases, assessment of lymph nodes must be considered particularly important when staging recurrent breast cancer [16–18].

[18F]-2-fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography (PET) is able to supply functional information for whole-body tumour staging [18–20]. Eubank et al [16] found a sensitivity, specificity and accuracy of 85%, 90% and 88%, respectively, for FDG-PET while staging mediastinal and intramammarian lymph nodes in patients with metastatic breast cancer. In comparison, CT was able to provide a sensitivity, specificity and accuracy of only 54%, 85% and 73% in these patients [16]. In addition, FDG-PET has shown a substantial impact on patient management [21].

However, PET alone is not without limitations for tumour staging; liver metastases may go undetected because of organ movement [22, 23]. Furthermore, in selected cases, non-FDG-avid lesions may also be undetected by FDG-PET. No consensus has been found so far concerning the role of PET in the detection of bone metastases, especially in patients after chemotherapy [24–26]. Therefore, a combined approach of CT and PET for patients with recurrent breast cancer may be advantageous to improve the accuracy of restaging and to tailor patient management. Combined PET/CT scanners have already shown a large impact on tumour staging, therapy response and therapeutic strategies in several oncological diseases [14, 22]. To date, very limited data are available on the value of dual modality PET/CT for restaging of breast cancer [27, 28].

The aim of this study was to evaluate the potential benefit of FDG-PET/CT in patients with recurrent breast cancer over CT alone, FDG-PET alone and PET+CT side by side image assessment. Accuracies for restaging (rTNM) of breast cancer as well as the impact on therapy planning were compared between the different imaging procedures.


   Methods and materials
Top
 Abstract
 Introduction
 Methods and materials
Results
 Discussion
 Conclusion
 References
 
Study design and data acquisition
For this single institutional (university hospital) evaluation, 44 patients undergoing PET/CT for restaging of breast cancer were included. The patients were included retrospectively in the study evaluation. Furthermore, patients were included consecutively concerning their referral for PET/CT examination.

All clinical and histopathological information was extracted from the patients' charts in agreement with the referring physicians. This included the TNM classification and localization of the primary tumour, the receptor status, the type of treatment, the time interval from first diagnosis until the first PET/CT and the current reason for FDG-PET/CT referral and consecutive therapy after PET/CT imaging.

Patient population
We evaluated PET/CT scans from 62 patients with a mean age of 56 years (range 36–80 years). Four patients had to be excluded because of a lack of sufficient follow-up information (clinical data or imaging), 14 patients had already known metastases, leaving 44 patients for final evaluation. The excluded patients had clear metastatic findings on cross-sectional imaging (CT or MRI) in conjunction with elevated tumour markers (n = 5) and/or histopathological verification of recurrence of breast cancer (n = 9) prior to their referral for the PET/CT examination in one body compartment. Thus, inclusion criteria were first suspicion of recurrence of breast cancer rather than whole-body staging in already confirmed cases of recurrence of breast cancer. All patients with already known metastases were therefore excluded from our evaluation. All other patients were scheduled for PET/CT on account of suspicion of tumour recurrence during their individual follow-up procedures; these were elevated tumour markers (n = 15), suspicious chest or bone X-ray findings (n = 10), suspicious physical examination with axillary lymph node findings or suspicion of local recurrence in conjunction with suspicious ultrasound findings (n = 12), suspicious abdominal ultrasound findings (n = 5) and equivocal findings on CT (n = 2).

The mean follow-up time of this patient population was 462 days (range 153–938 days). The mean time between primary diagnosis of breast cancer and referral to our institution was 70 months (range 5–276 months). 40 patients had a history of unilateral primary breast cancer; bilateral breast cancer had been initially diagnosed in four patients. Primary surgery was conducted in all patients (breast-preserving surgery n = 24; mastectomy n = 20). All patients had received additional chemotherapy or radiotherapy after the first diagnosis of breast cancer. The mean time interval between the last therapy cycle (chemotherapy or radiotherapy) and the restaging PET/CT study was 54 months (range 4–252 months). 30 patients received anti-hormonal therapy at the time of the PET/CT procedure, and 14 patients were without any therapy. All patients were assumed to be disease free after completion of their primary therapy. The distribution of the rTNM classification according to the standard of reference is shown in Table 1Go.


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  		Table 1. Distribution of rTNM classification according to the standard of reference

 
Written informed consent was obtained from all patients, and the study was performed in accordance with the regulations of the local institutional review board for retrospective analysis.

PET/CT imaging
Patients were instructed to fast for 4 h before the PET/CT procedure. The imaging procedure was performed 1 h after administering 340 MBq of FDG. Blood glucose levels were measured before the administration of FDG to ensure that they were in the normal range. All patients were instructed to drink a negative oral contrast agent during the FDG uptake time for optimized small bowel distension on CT. The solution contained 0.2% locust bean gum (LBG) and 2.5% mannitol (mannitol–LBG) dissolved in 1500 ml of water.

During the whole-body CT examination as part of the PET/CT examination, 140 ml of iodinated contrast agent (300 mmol ml–1 Xenetix 300; Guerbet GmbH, Germany) was administered intravenously according to a standardized protocol to ensure fully diagnostic CT data [29]. The contrast-enhanced CT was then used for the attenuation correction of the PET data. The CT was acquired in the caudocranial direction to avoid high-dose contrast artefacts in the subclavian vein. A start delay of 50 s was chosen for the CT acquisition after the beginning of contrast application. The first 90 ml of the contrast agent was injected at a rate of 3 ml s–1; the last 50 ml was injected at a rate of 1.5 ml s–1. The dual phase injection was intended to ensure full diagnostic (venous phase) CT data in the abdomen, whereas it represents a compromise protocol, thus a mixed arterial–venous phase in the thorax.

Dual modality, contrast-enhanced PET/CT was performed with a BiographTM system (Siemens Medical Solutions, Erlangen, Germany), which consists of a dual slice CT scanner (Somatom Emotion ) and a full ring PET tomograph (ECAT HR+ ) [30]. The PET provides an axial field of view of 15.5 cm per bed position and an in-plane spatial resolution of 4.6 mm. The system acquires the CT first, followed by the PET, which covers the same field of view (FOV) as whole-body CT. The FOV was defined to include an area from the base of the skull down to the upper thighs. Whole-body PET/CT was performed with the following CT data: 130 mAs, 130 kV, 5 mm slice thickness with a 2.4 incremental reconstruction and 8 mm table feed. The acquisition time of PET was tailored according to the patients' weight, calculating 3 min per bed position for patients up to 65 kg, 4 min up to 85 kg and 5 min over 85 kg. Corrected PET images were reconstructed iteratively (FORE-OSEM, two iterations, eight subsets, 128 x 128 matrix with a 5 mm gaussian smoothing). The images were acquired with a standardized limited breath-hold protocol to reduce breathing motion artefacts and to enhance diagnostic quality [31]. After the examination, CT and PET data sets were viewed separately and in fused mode on a commercially available computer workstation (SyngoTM software, Siemens Medical Solutions). Thus, all compared imaging modalities (PET alone, CT alone, PET+CT viewed side by side and combined in-line PET/CT) were derived from one data set.

Image evaluation
All imaging procedures were evaluated according to the latest edition of the American Joint Committee on Cancer (AJCC) classification for restaging breast cancer (rTNM) [32]. Blinded reviews of contrast-enhanced CT alone and FDG-PET alone were performed. CT images alone were assessed by two radiologists in consensus, PET images alone by two nuclear physicians in consensus. Side by side (PET + CT) images, as well as combined PET/CT images, were assessed by a radiologist and a nuclear physician in consensus. All reader groups had the same clinical information (patients with suspected recurrence of breast cancer), but were blinded to the results from the other reader teams. For all CT examinations, local tumour recurrences as well as distant metastases were evaluated based on the detection of pathological soft tissue lesions, their pattern of contrast enhancement, thickening of specific anatomical structures, the shape of those soft tissue lesions as well as the size of lymph nodes. Lymph nodes were considered to be malignant if their diameter exceeded 1 cm in size in the short axis on CT. Central necrosis was defined as a sign of malignancy as well, independently of lymph node size. Furthermore, according to standard CT criteria, a fatty hilum as well as calcifications were used as benign criteria for differentiation of benign and malignant lymph nodes on CT independently of lymph node size.

PET and PET/CT imaging were assessed quantitatively and qualitatively for areas of increased FDG uptake. Lesions were called malignant if the glucose utilization exceeded the surrounding tissue or blood pool level. The diagnosis of metastases was also supported by a maximum standardized uptake value (SUV) greater than 2.5 for malignant lesions extrahepatic and greater than 3.5 intrahepatic [33]. Evaluation of PET+CT and PET/CT was based on qualitative and quantitative measurements, and the results were found on a case to case basis in consensus. Assessment of metastatic spread to lymph nodes was assessed based on functional criteria rather than on morphological data on PET+CT and PET/CT. PET and PET/CT images were assessed with and without attenuation correction.

The impact on the patients' therapy was assessed by reviewing the patients' charts in consensus with the referring physicians, which contained the individual therapy based on the PET/CT findings. The assessment of a potential influence of PET/CT compared with CT alone and PET alone as well as side by side image evaluation on patient management was evaluated in consensus with the referring physicians based on the international ESMO guidelines [6]. Differences between the staging procedures were tested for statistical significance by McNemar's test.

Standard of reference
Histopathological confirmation of suspicious lesions (available in 15 patients) as well as a further clinical follow-up comprising physical examination, laboratory tests, tumour markers, other independent imaging studies such as CT, MRI, PET and/or PET/CT, X-ray studies, bone scans, ultrasound and mammography served as the standard of reference.

Criteria used for the standard of reference were: (1) biopsy findings; (2) clinical findings such as increasing tumour markers; (3) the combination of negative follow-up imaging findings and negative clinical findings; (4) combination of positive clinical findings at the time of PET/CT and decreasing size or resolution of the tumour during or after therapy as determined by follow-up imaging studies; (5) increasing size, number and/or metabolic activity during follow-up; (6) resolution of pathological findings on follow-up PET/CT studies combined with negative clinical follow-up.


   Results
Top
 Abstract
 Introduction
 Methods and materials
 Results
Discussion
 Conclusion
 References
 
Patients
rTNM staging
Overall, the presence of disease was established in 19 patients according to the standard of reference. 25 patients were defined as disease free at the time of the PET/CT procedure, which was verified by the standard of reference during follow-up (see above).

PET/CT was more accurate in the definition of rTNM stage (91%) than PET alone (82%), than CT alone (82%) and marginally more accurate than PET+CT (86%). All detected differences did not achieve a statistically significant level (p<0.05) (Table 2Go). All imaging procedures tended to overstage the patients' disease status (Figure 1Go).


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  		Table 2. Distribution of staging results according to the standard of reference

 

Figure 1
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  		Figure 1. 56-year-old patient with a history of left-sided breast cancer. (a) Axial CT image shows a contrast-enhancing mass at the right thorax wall under the lower part of the greater pectoral muscle (white arrow). CT suggested a distant metastasis. (b) Corresponding axial PET image shows an area with pathologically increased glucose metabolism at the right thorax wall, suggesting a distant metastasis as well (black arrow). (c) Corresponding PET/CT image shows the contrast-enhancing mass with elevated glucose metabolism (white arrow). However, histopathology revealed granulomatous tissue without malignancy. All imaging modalities were evaluated as false positive.

 
Potential influence on therapy
Overall, PET/CT correctly changed consecutive therapy compared with CT alone in five patients, compared with PET alone in four patients and in two patients compared with PET+CT. These differences between the compared imaging procedures can be explained based on several discordant findings.

PET/CT vs CT alone
CT alone suggested in one patient a malignant thyroid mass, in one patient pleural metastases and in one patient a spleen metastasis. However, these lesions were not assigned as malignant on PET/CT and further follow-up and turned out to be a thyroid adenoma, unspecific pleural post-inflammatory thickening (unchanged during follow-up and no further clinical suspicion of recurrence) and a haemangioma. On the other hand, one peritoneal metastasis and pathological lymph nodes were overlooked because of their small size, but detected by PET/CT (Figure 2Go).


Figure 2
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  		Figure 2. 67-year-old patient with a history of left-sided breast cancer. (a) Axial PET image shows an area with increased glucose metabolism in the left lower abdomen, suggesting a distant, peritoneal metastasis (black arrow). (b) Corresponding axial CT image was evaluated as negative for abdominal metastases. (c) Corresponding axial PET/CT image shows increased glucose metabolism in a small, contrast-enhancing mass directly beneath small bowel loops (white arrow). PET/CT suggested a peritoneal metastasis, which was confirmed by radiological and clinical follow up.

 
PET/CT vs PET alone
PET alone suggested axillary/cervical lymph node metastases in two patients; these were false-positive findings based on artificially elevated glucose metabolism in fat tissue and surrounding muscles (Figure 3Go). Furthermore, bone metastases were overlooked in two patients with PET alone, but detected with PET/CT.


Figure 3
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  		Figure 3. 44-year-old patient with a history of unilateral right-sided breast cancer and rising tumour markers. (a) Coronal whole-body PET image shows an area of increased glucose metabolism in the right supraclavicular fossa, indicating a malignant lymph node (black arrow). (b) Corresponding axial PET image confirmed a focal region of increased glucose metabolism (black arrow). (c) Axial CT image with no evidence of a contrast-enhancing mass or lymph node. (d) Corresponding PET/CT image detected the area of increased glucose metabolism in supraclavicular fatty tissue (black arrow). Overall, PET was evaluated as false positive; combined PET/CT supported the correct diagnosis.

 
PET/CT vs PET+CT viewed side by side
Impact on therapy of PET/CT over PET+CT was based on false-positive findings, which were correctly determined based on accurate fusion of both imaging procedures in PET/CT (fat tissue, muscle activity, lesions overlooked by one reader team)

Concomitant findings and local recurrence
In five patients, a locally recurrent breast cancer was suspected. However, in two patients with suspicion of recurrence, histopathology did not reveal any malignancy. In one patient, the suspicious lesion turned out to be a foreign body granuloma; in the second patient, an inflammatory soft tissue mass was detected (Figure 1Go). Both lesions were proved false positive by biopsy.

In two patients referred for restaging and suspicion of metastatic spread of breast cancer, an as yet unknown second tumour entity was detected, one colorectal cancer and one gastric cancer. Both malignancies were confirmed by histopathology after resection.


   Discussion
Top
 Abstract
 Introduction
 Methods and materials
 Results
 Discussion
Conclusion
 References
 
Several studies addressing different tumour entities have suggested an advantage of fused PET/CT over morphological and functional imaging procedures alone [15, 22]. However, only very little is known about the staging accuracy of PET/CT in recurrent breast cancer [28]. PET/CT was only slightly more accurate than PET + CT side by side evaluation concerning both staging and the influence on therapy management. Thus, either FDG-PET/CT or PET + CT may be considered appropriate for restaging of patients with breast cancer.

To date, there are several different studies available concerning the value of PET in diagnosing primary and recurrent breast cancer [34–37]. PET has shown sensitivities ranging from 93% to 100% for the detection of primary and recurrent breast cancer, whereas the specificity can be as low as 72% for recurrent cancer [19, 38]. For lymph node staging in recurrent breast cancer, Eubank et al reported sensitivities and specificities of 85% and 90% [16]. However, referring physicians and readers have to be aware of several pitfalls in PET when imaging patients with suspected recurrent breast cancer. PET imaging remains challenging for the localization of hypermetabolic lesions based on the limited spatial resolution and artificially high metabolic activity in fat tissue, muscle and bowel [39–41]. The visual combination of PET + CT improved the staging results of both CT alone and PET alone concerning staging accuracy and impact on therapy management in our study.

This was partly related to overlooked PET-negative sclerotic osseous metastases and lymph nodes with elevated glucose metabolism, which had to be rated as false-positive findings based on the standard of reference. In general, the most common reason for false-negative results on PET imaging is PET-negative (sclerotic) bone lesions [25, 35, 42]. While PET has shown high sensitivity when staging lytic or mixed lytic/blastic osseous metastases, only low detection rates have been reported in sclerotic lesions [43]. Thus, as PET appears not to be the staging procedure of choice for the detection of bone metastases, it might not be surprising that CT was able to add substantial information, especially in sclerotic, non-FDG-avid lesions.

However, it has to be taken into account that these particular patients in our study received prophylactic anti-hormonal medication. Thus, this may be a reason for the non-avidity of those lesions. As prophylactic anti-hormonal medication represents a standard method of care in breast cancer patients, dedicated studies are needed on this important topic to describe the long-term effect of anti-hormonal treatment on bone metastases in such a patient population.

In comparison with combined PET/CT, two lesions were overlooked on CT imaging based on their size. CT alone is already known to be limited for lymph node staging in several body compartments [16–18, 44 , 45]. Also, the detection of small structures may be challenging; thus, a small peritoneal metastasis was not detected because of its proximity to bowel loops. Other lesions were rated malignant on contrast-enhanced CT alone but turned out to be benign lesions. False-positive findings on CT can largely be explained by unspecific focal contrast enhancement that can possibly lead to wrong diagnosis based on post-therapy changes in conjunction with the given clinical background (restaging/suspicion of recurrence).

PET + CT showed slightly superior results to CT or PET alone, but combined PET/CT changed the staging results and prevented two patients from unnecessary therapy based on more accurate co-registration and localization of metabolic activity.

Combined PET/CT showed superior results in staging and impact on therapy in larger studies with an inhomogeneous patient population [15]. However, in restaging of breast cancer, little is known about side by side reading, and Fueger et al [28] have already suggested that careful PET + CT reading might lead to similar results compared with combined PET/CT. Although our study presented too small a number of patients to draw definitive conclusions, the time to definitive diagnosis and the psychological burden for patients might be decreased when staged with combined PET/CT rather than with two separate staging procedures.

Two out of five suspected local recurrences turned out to be false-positive findings in all imaging modalities. Inflammation is known to go along with an increase in glucose metabolism, which possibly renders differentiation of inflammation from malignancy on FDG-PET and PET/CT difficult. This must be considered a major limitation of PET and PET/CT when using FDG as a radioactive tracer. Thus, neither combined FDG-PET/CT nor one of the single modalities may be recommended as a first-line diagnostic tool for local restaging. However, morphological imaging methods such as MRI and CT can be particularly impaired by false-positive findings based on surrounding soft tissue changes and contrast enhancement patterns, which can mimic inflammation and/or malignant lesions and vice versa. Thus, in those cases, histopathological workup is needed to definitively exclude malignancy.

The development and implementation of alternative and more specific nuclides for breast cancer imaging or inflammation imaging (i.e. 18F-fluoroethyl-L-tyrosine (FET-PET), dual time point PET imaging) may overcome this limitation in functional imaging [46–48]. However, those imaging strategies have not achieved a widespread breakthrough in clinical routine yet. Dedicated studies and comparisons with morphological imaging methods are needed on that topic to prove a potential supremacy. Furthermore, it will also be important to assess whether combined imaging (i.e. PET/CT with specific tracers) can add additional value in the differentiation of malignant lesions and inflammatory lesions.

Limitations
The study faces some practical limitations. First of all, not all lesions found by imaging could be verified by biopsy. Several pitfalls have to be considered when using additional clinical and imaging follow up as the standard of reference. A "metabolic flare" phenomenon (increase in SUV under anti-hormonal therapy) has been described by Dehdashti and coworkers [49] in patients with metastatic breast cancer undergoing anti-hormonal therapy. As this phenomenon was noted in a shorter follow-up time than that evaluated here and imaging and clinical data were used in conjunction for follow-up assessment in our study, no difficulties were noted concerning this phenomenon in our patient population. As discussed, PET is known for low detection rates in sclerotic bone lesions. However, it is still unclear whether sclerotic bone lesions are "not active" metastases and, therefore, patients with only sclerotic lesions may have to be considered cured. In general, typically shaped sclerotic bone lesions after therapy are mostly accepted as metastases; thus, this approach was chosen for our evaluation as well. As discussed earlier, further studies are needed to define the dedicated effect of anti-hormonal medication on the FDG avidity of sclerotic bone lesions.

The CT component of the PET/CT protocol used represents a compromise in order to have full diagnostic contrast-enhanced CT data on the thorax and abdomen. However, with the scanner type used in this study, only one contrast phase was available, which might be a reason for falsely interpreted lesions in this study on CT alone. Thus, a mixed arterial–venous phase was available in the thorax, whereas a venous phase was available for the abdomen. With recently developed PET/CT scanners, a tailored, multiphase (i.e. dual or triple phase CT for the detection of arterially enhancing lesions), contrast-enhanced CT component in PET/CT will be possible to overcome such limitations. With the actual scanner generation used in our study, in selected cases, additional imaging procedures might be necessary.

Another limitation might be that image acquisition on a single system may have an effect concerning overestimation on side by side image evaluation. In our study, all compared imaging procedures (CT alone, PET alone, PET + CT viewed side by side as well as combined PET/CT) derived from one single, combined PET/CT data set to avoid additional radiation burden to the patient. In cases where combined PET/CT is not available, separate CT and PET data sets are typically acquired on independent imaging systems. Thus, differences in the coaxial imaging range, the respiration state and the location of movable organs between the two imaging procedures are to be expected. In contrast, images viewed side by side in our study were collected on the same imaging system with the same field of view and immediate acquisition of the PET data after CT in order to minimize organ shift. We tried to account for this limitation by manually misregistering the PET with respect to the CT for side by side image evaluation by displaying each imaging procedure on different screens. However, the PET and CT images were derived in this study from a single PET/CT acquisition and, therefore, a possible overestimation cannot be excluded.


   Conclusion
Top
 Abstract
 Introduction
 Methods and materials
 Results
 Discussion
 Conclusion
References
 
PET/CT correctly changed the staging results over PET alone and CT alone and, only slightly, over PET + CT alone. All detected differences did not achieve statistical significance. More importantly, although not statistically significantly different, combined PET/CT correctly changed consecutive therapy over CT and PET alone, but only marginally over PET + CT. However, based on the study design, a possible effect of overestimation of PET + CT evaluation compared with combined PET/CT cannot be excluded. Overall, the experienced physician will possibly be able to derive accurate results for patients with suspected recurrent breast cancer from visually fused PET + CT. Whether images are read side by side from different examinations or fused from a single PET/CT scan may, therefore, be based on local availability of CT, PET and combined PET/CT.

Current address: Dr Patrick Veit-Haibach, Department of Nuclear Medicine, University Hospital Zürich, Rämistrasse 100, 8091 Zürich, Switzerland.

Received for publication July 12, 2006. Revision received September 27, 2006. Accepted for publication October 2, 2006.


   References
Top
 Abstract
 Introduction
 Methods and materials
 Results
 Discussion
 Conclusion
 References
 

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