Malignant melanoma and 18F-FDG-PET: Should the whole body scan include the legs?

Determination of the optimal imaging protocol for [18F]PSMA-PET-CT for the detection of bone metastases in prostate cancer patients

AIM

Prostate-specific membrane antigen-positron emission tomography (PSMA-PET) is a widely used diagnostic tool in patients with prostate cancer (PC). However, due to the limited availability of PET scanners and relevant acquisition costs, it is important to consider the indications and acquisition time. The aim of this investigation was to determine whether a PET scan from the skull base to the proximal thigh is sufficient to detect the presence of bone metastases.

METHODS

A retrospective analysis was conducted on 1050 consecutive [18F]PSMA-1007-PET-CT scans from the head to the proximal lower leg. The PET scans were categorised according to the presence and amount of bone metastases: (1) 1-5, (2) 6-19 and (3) ≥20. Additionally, the PET scans were evaluated for the presence of bone metastases below the proximal thigh as well as bone metastases above the skull base. Imaging results were compared to patients PSA values.

RESULTS

Of the 391 patients with bone metastases, 146 (37.3%) exhibited metastases located below the proximal thigh and 104 (26.6%) above the skull base. The majority of bone metastases located below the proximal thigh (145, 99.3%) and above the skull base (94, 90.4%) were identified in patients with more than five bone metastases. No solitary distal metastasis was detected. The PSA value correlated significantly with number of bone metastases (e. g., 1-5 vs. ≥20 bone metastases, P < 0.001) and was significantly higher in patients with distal bone metastases (P < 0.001). ROC analysis showed that a PSA value of 11.15 ng/mL is the optimal cut-off for detecting bone metastases located below the proximal thigh, with an AUC of 0.919 (95% CI: 0.892-0.945, sensitivity 87%, specificity 86%). Similarly, the PSA value of 12.86 ng/mL is the optimal cut-off for detecting bone metastases above the skull base with an AUC of 0.904 (95% CI: 0.874-0.935, sensitivity 87%, specificity 83%).  CONCLUSION: PSMA-PET acquisition protocols from the skull base to the proximal femur may be sufficient to accurately detect bone metastatic disease in PC. PSA values can provide decision support for individual PET acquisition protocols.

Positron Emission Tomography/Computed Tomography Transformation of Oncology: Melanoma and Skin Malignancies

Skin cancers are the most common cancers, with melanoma resulting in the highest cause of death in this category. Accurate clinical, histologic, and imaging staging with fludeoxyglucose positron emission tomography (FDG PET) is most important to guide patient management. Whilst surgical excision with clear margins is the gold-standard treatment for primary cutaneous melanoma, targeted therapies have generated remarkable and rapid clinical responses in melanoma, for which FDG PET also plays an important role in assessment of treatment response and post-therapy surveillance. Non-FDG PET tracers, advanced PET technology, and PET radiomics may potentially change the landscape of the utilization of PET in the imaging of patients with cutaneous malignancies.

Practical Considerations When Interpreting FDG PET/CT Imaging for Staging and Treatment Response Assessment in Melanoma Patients

While FDG PET/CT bears a high sensitivity and specificity for the staging of stage III and IV melanoma as well as for the purpose of melanoma recurrence detection, overall results tend to vary from one part of the body to another as well as for melanoma from cutaneous or choroidal origin. In this paper, organ or site-related differences in sensitivity and specificity in melanoma patients, both from cutaneous and choroidal origin, as well as their impact on clinical decision making are discussed. Furthermore, with the advent of immunotherapy for the treatment of malignant melanoma, post-treatment related potential false positive findings have emerged, the knowledge of which is essential for accurate treatment response assessment. These post-treatment related potential false positive findings are summarized in this paper so as to help the nuclear medicine physician in avoiding erroneous interpretation of acquired FDG PET/CT images in melanoma patients receiving immuntherapy.

Malignant Cutaneous Melanoma: Updates in PET Imaging

BACKGROUND

Cutaneous malignant melanoma is a neoplasm whose incidence and mortality are dramatically increasing. 18F-FDG PET/CT gained clinical acceptance over the past 2 decades in the evaluation of several glucose-avid neoplasms, including malignant melanoma, particularly for the assessment for distant metastases, recurrence and response to therapy.

OBJECTIVE

To describe the advancements of nuclear medicine for imaging melanoma with particular attention to 18F-FDG-PET and its current state-of-the-art technical innovations.

METHODS

A comprehensive search strategy was used based on SCOPUS and PubMed databases. From all studies published in English, we selected the articles that evaluated the technological insights of 18FFDG- PET in the assessment of melanoma.

RESULTS

State-of-the-art silicon photomultipliers based detectors ("digital") PET/CT scanners are nowadays more common, showing technical innovations that may have beneficial implications for patients with melanoma. Steady improvements in detectors design and architecture, as well as the implementation of both software and hardware technology (i.e., TOF, point spread function, etc.), resulted in significant improvements in PET image quality while reducing radiotracer dose and scanning time.

CONCLUSION

Recently introduced digital PET detector technology in PET/CT and PET/MRI yields higher intrinsic system sensitivity compared with the latest generation analog technology, enabling the detection of very small lesions with potential impact on disease outcome.

18F-FDG PET/CT in the detection of asymptomatic malignant melanoma recurrence

Aim: To evaluate the diagnostic accuracy of FDG PET/CT in the detection of asymptomatic recurrence in patients with malignant melanoma who have had resection of their primary lesion. We also aimed to determine the pattern and factors predisposing to disease recurrence. Methods: Patients with malignant melanoma who have had surgical resection of their disease and without any clinical evidence of disease recurrence were followed- up with FDG PET/CT. The diagnostic accuracy of FDG PET/CT, pattern of recurrence and factors predictive of disease recurrence were determined. Results: A total of 144 patients were followed-up for a median period of 50.50 months. Asymptomatic recurrence was seen in 37 patients (25.7 %) with a median time to recurrence of 20 months. Lymph node was the commonest site of asymptomatic recurrence. Sex, tumour depth, histology type and presence of nodal metastasis were significant predictors of tumour recurrence. Age, race, site of primary lesion, type of lymph node resection were not significant predictors of disease recurrence. Race has a significant effect on the histological subtype of tumour (nodular maligna was more common in Caucasian while acral lentiginous was more prevalent in the Blacks) and the site of the primary lesion (lower limb in Blacks and trunk in Caucasians). Sensitivity, specificity and accuracy of FDG PET/CT for the detection of disease recurrence were 94.5 %, 87.6 % and 89.6 % respectively. Conclusion: FDG PET/CT is a suitable modality for early detection of asymptomatic recurrence of malignant melanoma. Asymptomatic recurrence most commonly occurs in lymph nodes. Sex, nodal metastasis and tumour pathologic features are predictors of recurrence.

Clinical relevance of 18F-FDG PET/CT lower-limb imaging in patients with malignant cutaneous melanoma

OBJECTIVE

The aim of this study was to assess the clinical relevance of imaging the lower limbs when using 2-(F)-fluoro-2-deoxy-D-glucose (F-FDG) positron emission tomography with computed tomography (PET/CT) for malignant cutaneous melanoma in patients without previously known or suspected primary or metastatic melanoma lesions in the lower limbs.

PATIENTS AND METHODS

We retrospectively assessed 880 consecutive F-FDG PET/CT scans performed for adult patients in a context of suspected melanoma spanning a period of 5 years. All scans were correlated with the associated patient records (clinical history, physical examinations, and pathology reports), as well as follow-up imaging examinations, up until at least 6 months after the end of the study.

RESULTS

Among the 461 whole-body scans included for analysis, 109 reported unusual activity in the lower limbs, but with at most 21 scans showing lower-limb lesions attributed to melanoma on follow-up. No scan showed melanoma lesions exclusively in the lower limbs, and in no case did imaging the lower limbs upstage a patient. Imaging the lower limbs changed the actual clinical management of the melanoma for only one patient, with precautionary local radiation therapy administered following the detection of an asymptomatic distal femur bone metastasis in an otherwise plurimetastatic patient headed for palliative care.

CONCLUSION

Our study, the largest of its kind, confirms that, when using F-FDG PET/CT for staging, restaging, or surveillance of malignant cutaneous melanoma in patients without previously known or suspected lower-limb melanoma lesions, imaging the lower extremities offers little additional clinically relevant information and stopping the scan at the proximal thighs has essentially no clinical impact.

Clinical and therapeutic impact of 18F-FDG PET/CT whole-body acquisition including lower limbs in patients with malignant melanoma

OBJECTIVES

To assess the added benefit of scanning lower limbs in addition to the usual whole-body positron emission tomography/computed tomography (PET/CT) scan in patients with no known or suspected primary or metastatic melanoma involving the lower limbs.

MATERIALS AND METHODS

This is a retrospective study of 122 consecutive patients [174 2-[¹⁸F]-fluoro-2-deoxy-D-glucose (FDG) PET/CT] who underwent FDG PET/CT for staging of melanoma at different time points in the course of the disease from October 2005 to February 2009 at the Brest University Hospital. Reports of whole-body PET/CT scans including lower limbs were reviewed. PET/CT abnormalities on the lower extremities were tabulated by location and correlated with pathology, other imaging studies and at least a 6-month clinical follow-up. The usefulness of lower limbs acquisition in clinical management was evaluated according to imagery findings.

RESULTS

Among the 174 consecutive PET/CT scans performed in 122 patients, 33 scans in 28 patients highlighted abnormal FDG uptakes considered as equivocal or suggestive of malignancy in the lower limbs. In 28 cases, uptakes were located at once in the lower limbs and in the rest of the body (lung, liver, mediastinal and sub-diaphragmatic lymph nodes, adrenal glands, bone) corresponding to disseminated disease. In five cases, PET/CT uptakes were located only in lower limbs; each pathological uptake corresponded to benign lesions. Lower limbs findings never impacted clinical and therapeutic decision.

CONCLUSION

Lower limbs additional PET/CT acquisition seems to offer poor additional benefit with none unexpected lesion detected and routine skull base to upper thigh images might be sufficient for this subset of patients.

Melanoma

This chapter discusses the value of FDG-PET and combined FDG-PET/CT in staging and follow-up of melanoma patients. For melanoma patients, the presence or absence of regional lymph node metastases is one of the most important prognostic factors; the recent development of sentinel lymph node biopsy offers a highly sensitive staging method. FDG-PET has shown a limited sensitivity to detect microscopic lymph node metastases in this selected group of patients with stages I and II melanoma. However, for the detection of distant metastases, FDG-PET is frequently used. Although there is no consensus, some surgeons pursue surgical excision of metastatic disease if only one or a few sites of disease are apparent. Precise identification of the location and number of metastatic lesions could therefore be important for surgical planning. Even though patients with metastatic melanoma generally have a poor prognosis (5-year survival 3-16%), there is still a need for accurate staging. Firstly, to identify those patients who may benefit from a surgical procedure, while avoiding these potentially harmful surgical procedures for patients with multiple distant metastases. Secondly, accurate staging is important to improve the efficiency of clinical trials, and thirdly, to provide patients with detailed information about their prognosis. Taking the published literature together, and reasoning that FDG-PET/CT is the current standard in PET imaging, there may be a case for the combined PET/CT in the setting of metastatic melanoma. However, further research is needed as the benefit of the combined FDG-PET/CT vs. FDG-PET alone seems to be less than reported for other tumor entities, which may be due to the high avidity of melanoma for FDG, so that many of the metastases are detected with FDG-PET and the additional CT does not increase the sensitivity.

Clinical value of including the head and lower extremities in 18F-FDG PET/CT imaging for patients with malignant melanoma

OBJECTIVE

To assess the added benefit of scanning lower extremities and skull in addition to 'skull base to upper thigh' images in PET/CT evaluation of metastatic melanoma.

SUBJECTS/METHODS

Reports of consecutive whole-body PET/CT scans from January 2003 to March 2006 in patients with melanoma were retrospectively reviewed. PET abnormalities in the brain/scalp and lower extremities were tabulated by location and whether they were 'anticipated' or 'unanticipated' based on previously available data. Findings were correlated with pathology, other imaging studies, and clinical follow-up.

RESULTS

Two hundred and ninety-six PET/CT examinations in 173 patients with melanoma were included. Twenty-five of the 296 (8.4%) scans showed brain/scalp abnormalities. Of these, only four (1.4% of all scans) showed unanticipated abnormalities: two were false positive findings, and two (0.7% of all scans) represented metastases in addition to multiple other metastases in the usual field of view. Fifty-nine of the 296 (19.9%) scans showed lower extremity abnormalities. Of these, 13 (4.4% of all scans) showed unanticipated abnormalities which were equivocal or suggestive of malignancy: eight (2.7% of all scans) represented metastases in addition to multiple other metastases in the usual field of view, and five represented false positive findings. In no case was an unanticipated isolated malignant lesion identified in the brain/scalp or lower extremities.

CONCLUSIONS

In patients with no known or suspected primary or metastatic melanoma involving the head or extremities, inclusion of these regions on PET/CT is of low yield and appears to offer little significant additional benefit, as detection of additional metastases in these patients is unlikely to change clinical management. Routine skull base to upper thigh images may be adequate for this subset of patients with melanoma.

Novel Imaging Techniques in Melanoma

Cutaneous melanoma is one of the most deadly malignancies. Although it accounts for approximately 4% of all cancer cases, it ac-counts for approximately 79% of skin cancer-related deaths. In the past few years, the nuclear medicine platform used in the management of melanoma has extended to biochemical and structural imaging. In clinical practice, integrated positron emission tomography/CT devices allow anatomic and metabolic characterization of meta-static disease in a single study. Similarly, more accurate localization of sentinel nodes in a 3-D space now is feasible with hybrid single photon emission CT/CT system. In translational research, [18F]fluorodeoxyglucose probes have been designed to optimize the detection of melanoma tumor sites in vivo.

Can body volume be determined by PET?

PURPOSE

To avoid dependence on body weight, the standardised uptake value (SUV) in positron emission tomography (PET) can instead be normalised to the lean body mass (LBM), which can be determined from body volume and mass. This study was designed to answer the following questions: Firstly, can the total body volume in principle be determined using PET? Secondly, is the precision of this measurement comparable to that achieved using an established standard method.

METHODS

Ten patients were examined during oncological whole-body PET examinations. The whole-body volume of the patients was determined from the transmission scan in PET. Air displacement plethysmography with BOD POD was used for comparison as the standard method of volume determination.

RESULTS

In all patients, the whole-body volumes could be determined using PET and the standard method. Bland and Altman [23] analysis for agreement between the volumes determined by the two methods (presentation of differences vs means) revealed a very small difference of -0.14 l. With a mean patient volume of 71.81+/-15.93 l, the relative systematic error is only <0.1%. On this basis, equality of the volume values determined by the two methods can be assumed.

CONCLUSION

PET can be used as a supplementary method for experimental determination of whole-body volume and total body fat in tumour patients. The fat content can be used to calculate the LBM and to determine body weight-independent SUVs (SUV(LBM)).