Comparison of Manual and Semi-Automatic [18F]PSMA-1007 PET Based Contouring Techniques for Intraprostatic Tumor Delineation in Patients With Primary Prostate Cancer and Validation With Histopathology as Standard of Reference.

Simon K B Spohn,August Sigle,Lara Ceci,Selina Kiefer,Cordula A Jilg,Constantinos Zamboglou,Thomas F Fassbender,Wolfgang Schultze-Seemann,Anca L Grosu,Juri Ruf,Maria Kramer,Tanja Sprave,Peter Bronsert,Nils H Nicolay

doi:10.3389/fonc.2020.600690

Abstract

PurposeAccurate contouring of intraprostatic gross tumor volume (GTV) is pivotal for successful delivery of focal therapies and for biopsy guidance in patients with primary prostate cancer (PCa). Contouring of GTVs, using 18-Fluor labeled tracer prostate specific membrane antigen positron emission tomography ([18F]PSMA-1007/PET) has not been examined yet.Patients and MethodsTen Patients with primary PCa who underwent [18F]PSMA-1007 PET followed by radical prostatectomy were prospectively enrolled. Coregistered histopathological gross tumor volume (GTV-Histo) was used as standard of reference. PSMA-PET images were contoured on two ways: (1) manual contouring with PET scaling SUVmin-max: 0–10 was performed by three teams with different levels of experience. Team 1 repeated contouring at a different time point, resulting in n = 4 manual contours. (2) Semi-automatic contouring approaches using SUVmax thresholds of 20–50% were performed. Interobserver agreement was assessed for manual contouring by calculating the Dice Similarity Coefficient (DSC) and for all approaches sensitivity, specificity were calculated by dividing the prostate in each CT slice into four equal quadrants under consideration of histopathology as standard of reference.ResultsManual contouring yielded an excellent interobserver agreement with a median DSC of 0.90 (range 0.87–0.94). Volumes derived from scaling SUVmin-max 0–10 showed no statistically significant difference from GTV-Histo and high sensitivities (median 87%, range 84–90%) and specificities (median 96%, range 96–100%). GTVs using semi-automatic segmentation applying a threshold of 20–40% of SUVmax showed no significant difference in absolute volumes to GTV-Histo, GTV-SUV50% was significantly smaller. Best performing semi-automatic contour (GTV-SUV20%) achieved high sensitivity (median 93%) and specificity (median 96%). There was no statistically significant difference to SUVmin-max 0–10.ConclusionManual contouring with PET scaling SUVmin-max 0–10 and semi-automatic contouring applying a threshold of 20% of SUVmax achieved high sensitivities and very high specificities and are recommended for [18F]PSMA-1007 PET based focal therapy approaches. Providing high specificities, semi-automatic approaches applying thresholds of 30–40% of SUVmax are recommend for biopsy guidance.

Highlights

Accurate intraprostatic tumor contouring is pivotal for successful delivery of high precision focal therapies of primary prostate cancer (PCa) and biopsy guidance
Gross tumor volume (GTV) from scaling SUVmin-max 0–5 were significantly larger than GTV Histo
PSMA-PET/CT has been established as a promising diagnostic method for identification of intraprostatic lesions [24]. [68Ga] PSMA is a widely used tracer with excellent performance [9, 11], but new tracers like [18F]PSMA-1007 have been developed in recent years with putative benefits in terms of lesser renal elimination and consequent less background signal in the bladder [15], simplified manufacturing [18], and lesion detection [16]

Summary

Introduction

Accurate intraprostatic tumor contouring is pivotal for successful delivery of high precision focal therapies of primary prostate cancer (PCa) and biopsy guidance. In primary PCa results from our workgroup as well as other studies suggest that PSMA-PET shows better sensitivities with comparable specificity than mpMRI in intraprostatic lesions detection [11, 12], gives complementary information [13] and may be favorable for focal therapy guidance [14]. Since [68Ga]- and [18F]PSMA-1007 tracers show differences in SUV distribution scaling recommendations might not be used interchangeable [17] This prospectively designed study aims to validate [18F]PSMA-1007 PET based contouring approaches for intraprostatic tumor contouring using whole mount histopathology as standard of reference, since a consensual method to accurately contour intraprostatic lesions for this tracer has not yet been established

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