Staging the axilla in breast cancer patients with 18F-FDG PET: how small are the metastases that we can detect with new generation clinical PET systems?

Dimitri Bellevre,Christelle Levy,Jean-Marc Guilloit,Jean-Michel Grellard,Cécile Blanc Fournier,Audrey Emmanuelle Dugué,Djelila Allouache,Nicolas Aide,Cédric Desmonts,Odile Switsers,Hubert Crouet

doi:10.1007/s00259-014-2689-7

Abstract

PurposePoint spread function (PSF) reconstruction improves spatial resolution throughout the entire field of view of a PET system and can detect smaller metastatic deposits than conventional algorithms such as OSEM. We assessed the impact of PSF reconstruction on quantitative values and diagnostic accuracy for axillary staging of breast cancer patients, compared with an OSEM reconstruction, with emphasis on the size of nodal metastases.MethodsThis was a prospective study in a single referral centre in which 50 patients underwent an 18F-FDG PET examination before axillary lymph node dissection. PET data were reconstructed with an OSEM algorithm and PSF reconstruction, analysed blindly and validated by a pathologist who measured the largest nodal metastasis per axilla. This size was used to evaluate PET diagnostic performance.ResultsOn pathology, 34 patients (68 %) had nodal involvement. Overall, the median size of the largest nodal metastasis per axilla was 7 mm (range 0.5 – 40 mm). PSF reconstruction detected more involved nodes than OSEM reconstruction (p = 0.003). The mean PSF to OSEM SUVmax ratio was 1.66 (95 % CI 1.01 – 2.32). The sensitivities of PSF and OSEM reconstructions were, respectively, 96 % and 92 % in patients with a largest nodal metastasis of >7 mm, 60 % and 40 % in patients with a largest nodal metastasis of ≤7 mm, and 92 % and 69 % in patients with a primary tumour ≤30 mm. Biggerstaff graphical comparison showed that globally PSF reconstruction was superior to OSEM reconstruction. The median sizes of the largest nodal metastasis in patients with nodal involvement not detected by either PSF or OSEM reconstruction, detected by PSF but not by OSEM reconstruction and detected by both reconstructions were 3, 6 and 16 mm (p = 0.0064) respectively. In patients with nodal involvement detected by PSF reconstruction but not by OSEM reconstruction, the smallest detectable metastasis was 1.8 mm.ConclusionAs a result of better activity recovery, PET with PSF reconstruction performed better than PET with OSEM reconstruction in detecting nodal metastases ≤7 mm. However, its sensitivity is still insufficient for it to replace surgical approaches for axillary staging. PET with PSF reconstruction could be used to perform sentinel node biopsy more safely in patients with a primary tumour ≤30 mm and with unremarkable PET results in the axilla.Electronic supplementary materialThe online version of this article (doi:10.1007/s00259-014-2689-7) contains supplementary material, which is available to authorized users.

Highlights

Breast cancer is the most frequent malignancy in women in Western countries and the second leading cause of cancerrelated deaths among women
For evaluation of the spatial resolution of the PET system with Point spread function (PSF) and OSEM reconstructions, rather than computing Full-width at half-maximum (FWHM) in air as recommended in the National Electrical Manufacturers Association (NEMA) standards, we evaluated FWHM in the geometry of a human breast and axilla PET examination by placing linear sources at a 15-cm radial offset on both sides of an anthropomorphic phantom filled with an activity in the range of the average activity expected in a human body
Radial FWHM was measured on four linear sources and ranged from 2.35 mm to 2.48 mm for PSF reconstruction and from 6.19 mm to 6.46 mm for OSEM reconstruction

Summary

Introduction

Breast cancer is the most frequent malignancy in women in Western countries and the second leading cause of cancerrelated deaths among women. In newly diagnosed breast cancer, 18F-FDG PET is not recommended for routine staging of axillary lymph nodes because its sensitivity is too low [1]. A recent systematic review found that the sensitivity of PET/ CT systems in the detection of axillary nodal metastases ranges from 44 % to 67 % [6]. This low sensitivity is due in part to the limited spatial resolution of PET systems, leading to partial volume effects (PVE) that cause significant underestimation of the radioactivity concentration in lesions smaller than two to three times the spatial resolution of the system. Small cancer deposits and especially micrometastases (

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