Abstract
PurposeMetabolically active tumour volume (MATV) is a potential quantitative positron emission tomography (PET) imaging biomarker in melanoma. Accumulating data indicate that low MATV may predict increased chance of response to immunotherapy and overall survival. However, metastatic melanoma can present with numerous (small) tumour lesions, making manual tumour segmentation time-consuming. The aim of this study was to evaluate multiple semi-automatic segmentation workflows to determine reliability and reproducibility of MATV measurements in patients with metastatic melanoma.MethodsAn existing cohort of 64 adult patients with histologically proven metastatic melanoma was used in this study. 18F-FDG PET/CT diagnostic baseline images were acquired using a European Association of Nuclear Medicine (EANM) Research Limited–accredited Siemens Biograph mCT PET/CT system (Siemens Healthineers, Knoxville, USA). PET data were analysed using manual, gradient-based segmentation and five different semi-automatic methods: three direct PET image–derived delineations (41MAX, A50P and SUV40) and two based on a majority-vote approach (MV2 and MV3), without and with (suffix ‘+’) manual lesion addition. Correlation between the different segmentation methods and their respective associations with overall survival was assessed.ResultsCorrelation between the MATVs derived by the manual segmentation and semi-automated tumour segmentations ranged from R2 = 0.41 for A50P to R2 = 0.85 for SUV40+ and MV2+, respectively. Manual MATV segmentation did not differ significantly from the semi-automatic methods SUV40 (∆MATV mean ± SD 0.08 ± 0.60 mL, P = 0.303), SUV40+ (∆MATV − 0.10 ± 0.51 mL, P = 0.126), MV2+ (∆MATV − 0.09 ± 0.62 mL, P = 0.252) and MV3+ (∆MATV − 0.03 ± 0.55 mL, P = 0.615). Log-rank tests showed statistically significant overall survival differences between above and below median MATV patients for all segmentation methods with areas under the ROC curves of 0.806 for manual segmentation and between 0.756 [41MAX] and 0.807 [MV3+] for semi-automatic segmentations.ConclusionsSimple and fast semi-automated FDG PET segmentation workflows yield accurate and reproducible MATV measurements that correlate well with manual segmentation in metastatic melanoma. The most readily applicable and user-friendly SUV40 method allows feasible MATV measurement in prospective multicentre studies required for validation of this potential PET imaging biomarker for clinical use.
Highlights
Metastatic melanoma has evolved from being an incurable disease with notoriously poor prognosis to a cancer type with the potential of long-term survival in patients with durable responses to immunotherapy [1,2,3,4,5]
In patients treated with immune checkpoint inhibitors, baseline metabolically active tumour volume (MATV) was associated with survival after correction for lactate dehydrogenase (LDH) level and presence of brain metastases [11, 13, 15]
All adult patients with histologically proven cutaneous or mucosal metastatic melanoma (American Joint Committee on Cancer [AJCC] [10] 7th edition stage IV melanoma) without prior systemic treatment and with a baseline 18F-FDG positron emission tomography (PET)/CT scan performed between May 2014 and December 2015 with PET-positive lesions were included in the cohort
Summary
Metastatic melanoma has evolved from being an incurable disease with notoriously poor prognosis to a cancer type with the potential of long-term survival in patients with durable responses to immunotherapy [1,2,3,4,5]. Patient and tumour characteristics that are both prognostic and predictive for response to immunotherapy, such as an elevated serum lactate dehydrogenase (LDH) level and the presence of brain metastases, are far from perfect in predicting which patients will benefit [10,11,12]. High baseline (metabolically active) tumour burden is associated with worse treatment outcome and poor survival in patients with metastatic melanoma [11, 13,14,15,16]. Besides visual identification of metastases, quantitative parameters including metabolically active tumour volume (MATV) can be measured using these baseline 18F-FDG PET images. In patients treated with immune checkpoint inhibitors, baseline MATV was associated with survival after correction for LDH level and presence of brain metastases [11, 13, 15]
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