Improved detection of in-transit metastases of malignant melanoma with BSREM reconstruction in digital [18F]FDG PET/CT

Virginia Liberini,Daniela Mihic-Probst,Stephan Skawran,Lars Husmann,Ken Kudura,Michael Messerli,Désirée Deandreis,Niels Rupp,Martin W Huellner,Daniele A Pizzuto,Reinhard Dummer,Alexander Maurer,Hannes Grünig,Erika Orita,Joanna Mangana

doi:10.1007/s00330-021-07852-7

Abstract

ObjectivesTo compare block sequential regularized expectation maximization (BSREM) and ordered subset expectation maximization (OSEM) for the detection of in-transit metastasis (ITM) of malignant melanoma in digital [18F]FDG PET/CT.MethodsWe retrospectively analyzed a cohort of 100 [18F]FDG PET/CT scans of melanoma patients with ITM, performed between May 2017 and January 2020. PET images were reconstructed with both OSEM and BSREM algorithms. SUVmax, target-to-background ratio (TBR), and metabolic tumor volume (MTV) were recorded for each ITM. Differences in PET parameters were analyzed with the Wilcoxon signed-rank test. Differences in image quality for different reconstructions were tested using the Man-Whitney U test.ResultsBSREM reconstruction led to the detection of 287 ITM (39% more than OSEM). PET parameters of ITM were significantly different between BSREM and OSEM reconstructions (p < 0.001). SUVmax and TBR were higher (76.5% and 77.7%, respectively) and MTV lower (49.5%) on BSREM. ITM missed with OSEM had significantly lower SUVmax (mean 2.03 vs. 3.84) and TBR (mean 1.18 vs. 2.22) and higher MTV (mean 2.92 vs. 1.01) on OSEM compared to BSREM (all p < 0.001).ConclusionsBSREM detects significantly more ITM than OSEM, owing to higher SUVmax, higher TBR, and less blurring. BSREM is particularly helpful in small and less avid lesions, which are more often missed with OSEM.Key Points• In melanoma patients, [18F]FDG PET/CT helps to detect in-transit metastases (ITM), and their detection is improved by using BSREM instead of OSEM reconstruction.• BSREM is particularly useful in small lesions.

Highlights

Material and methodsCutaneous malignant melanoma (CMM) is the 5th most common cancer in men and the 6th most common cancer in women worldwide [1, 2]
In-transit metastasis (ITM) occur in 2–10% of melanoma patients and are frequently associated with the development of nodal and/or systemic metastases [10], even in sentinel node-negative patients [11]
Based on PET Response Criteria in Solid Tumors (PERCIST), we considered a change in PET parameters of ± 30% (BSREM vs. ordered subset expectation maximization (OSEM)) as clinically relevant [30]

Summary

Introduction

Material and methodsCutaneous malignant melanoma (CMM) is the 5th most common cancer in men and the 6th most common cancer in women worldwide [1, 2]. Cutaneous and subcutaneous melanoma metastases are very frequent and include microsatellite, satellite, and intransit metastases (ITMs). With the 8th edition of the American Joint Committee on Cancer (AJCC), these three different entities were merged into the single subcategory “c” of the N classification (N1c, N2c, and N3c) [4]. The association of such metastases with poor prognosis was demonstrated by several studies [5,6,7,8,9]. ITMs occur in 2–10% of melanoma patients and are frequently associated with the development of nodal and/or systemic metastases [10], even in sentinel node-negative patients [11]. In 2015, Beasley et al [12] have reported a 5-year survival rate of 59% in patients without regional nodal disease compared to 19% for those with nodal disease (including ITM)

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