How to scan who: the delicate balance between selecting the patient and selecting the imaging protocol

Abstract

In this issue of the EJNMMI, Spadafora et al. propose shortening the FDG PET/CT acquisition for evaluating a solitary pulmonary nodule. The rationale is to design a strategy with a better cost-effectiveness ratio. There is a lot to like in the paper, as it discusses various aspects highly relevant to clinical nuclear medicine, such as clinical impact, patients' selection, imaging methodology, radiation safety, and costs. The objective is quite ambitious, as the proposed strategy could increase the number of FDG PET/CT performed for characterizing lung nodules, improve its effectiveness while reducing the cost and the radiation burden, and finally, increase the diagnostic accuracy. While some of these objectives may very well be achieved through this new strategy, it appears difficult to reach all, and there remain many question marks preventing the straight passage from the idea to the routine implementation.The first issue is the patient's selection. The current guidelines essentially use two criteria for deciding whether FDG PET/CT is indicated: the size of the nodule and the pre-test probability. It is important to note that the strategies discussed here exclusively concern solid nodules. FDG PET/CT should be performed for characterizing nodules > 8 mm in diameter with a pretest probability of malignancy that is low to moderate (5-65 %) [1] or ≥ 10 % [2]. The European guidelines are more complex, as it is recommended that indeterminate SPNs should be assessed, in light of all relevant information, including patient, epidemiological and procedure-related factors by expert multidisciplinary boards who will apply criteria such as those proposed by the Fleischner Society, which recommends considering PET in lesions > 8 mm [3,4]. In patients with a very high risk of cancer, the indication becomes staging rather than characterization [1]. Spadafora et al. imply that wholebody imaging is not indicated in T1 tumours, thanks to the low incidence of distant metastases in these early-stage lesions. This contradicts every international guideline for staging lung cancer [5][6][7], including small-cell lung cancer [8]. Indeed, even though lung cancer is increasingly diagnosed at an earlier stage, the majority of NSCLC patients have distant metastases at the time of diagnosis [9]. Even though the occurrence and distribution of distant metastases may occur following specific patterns, it remains practically impossible to predict such occurrence in individual patients [10]. Even in T1 tumors, the incidence of metastases is not negligible, as M1 disease has been reported in 13-14 % of the cases [11,12]. It is of primary importance that these patients are correctly identified in order to receive the optimal treatment, which may lead to prolonged survival in a subgroup presenting with synchronous oligometatastic NSCLC, i.e. with maximum five metastatic lesions [13]. PET/CT won't recognize all distant lesions, in particular the brain is not appropriately explored with PET alone. However, although the exact figure of extracerebral...

Risk-related 18F-FDG PET/CT and new diagnostic strategies in patients with solitary pulmonary nodule: the ITALIAN multicenter trial

“…The segmental approach has some clinical and practical drawbacks [16,20]. The first is the inability to complete SPN staging.…”

“…Although incidental findings on wb-PET/CT may represent a different pathology, the risks of over-diagnosis and over-treatment should be considered [10,30]. Some disadvantages in terms of practicability of s-PET/CT are due to Bon-the-fly^decisions to complete the study with a subsequent wb-PET/CT acquisition [20]. With modern equipment this approach would require only a few minutes.…”

“…Segmental (s-PET/ CT), i.e. limited to a thoracic acquisition, could be a costeffective approach in SPN [17][18][19] but the absence of studies leaves several questions unanswered [20]. The aim of this retrospective multicenter study was to compare the results of thoracic s-PET/CT to those of wb-PET/CT in a large cohort of patients with SPN in order to assess: (a) the feasibility of s-PET/CT without a significant loss in clinical information, (b) the possibility to identify patients in whom wb-PET/CT is necessary, and (c) the advantages and disadvantages of s-PET/CT in SPN.…”

Local imaging to interpret tumor size in F18 fluorodeoxyglucose positron emission tomography/CT in lung cancers

“…By shortening the scanning time, time can be created for respiratory gating and dual-phase imaging, in turn improving diagnostic accuracy. Local imaging can improve the balance between the cost and effectiveness of PET/CT scans in patients with SPN [16][17][18] .…”