The aim of this study was to analyze patterns of persistent versus recurrent or new PET lesions in a selected patient cohort with prostate-specific antigen (PSA) persistence after salvage lymph node dissection (SLND) and pre-procedure and post-procedure prostate-specific membrane antigen (PSMA) ligand PET. Methods: Sixteen patients were included in this multicenter study. The inclusion criteria were PSMA PET performed for biochemical recurrence before SLND (pre-SLND PET) and repeat PSMA PET performed for a persistently elevated PSA level (≥0.1 ng/mL) at least 6 wk after SLND (post-SLND PET). Image analysis was performed by 3 independent nuclear medicine physicians applying the molecular imaging TNM system PROMISE. Lesions were confirmed by histopathology, presence on correlative CT/MRI/bone scanning, or PSA response after focal therapy. Results: Post-SLND PET identified prostate cancer lesions in 88% (14/16) of patients with PSA persistence after SLND. Median PSA was 1.2 ng/mL (interquartile range, 0.6-2.8 ng/mL). Disease was confined to the pelvis in 56% of patients (9/16), and most of these men had common iliac (6/16, 38%) and internal iliac lymph node metastases (6/16, 38%). Extrapelvic disease was detected in 31% of patients (5/16). In pre- and post-SLND PET comparison, 10 of 16 had at least one lesion already detected at baseline (63% PET persistence), 4 of 16 had new lesions only (25% PET recurrence), and 2 had no disease on post-SLND PET. All validated regions (11 regions in 9 patients) were true-positive. Nine of 14 (64%) patients underwent repeat local therapies after SLND (7/14 radiotherapy, 2/14 surgery). Conclusion: SLND of pelvic nodal metastases was often not complete according to PSMA PET. About two thirds of patients had PET-positive nodal disease after SLND already seen on pre-SLND PSMA PET. Notably, about one quarter of patients had new lesions, not detected by presurgical PSMA PET.

Ob jectives

The European Society of Radiology identified 10 common indications for computed tomography (CT) as part of the European Study on Clinical Diagnostic Reference Levels (DRLs, EUCLID), to help standardize radiation doses. The objective of this study is to generate DRLs and median doses for these indications using data from the UCSF CT International Dose Registry.

Methods

Standardized data on 3.7 million CTs in adults were collected between 2016 and 2019 from 161 institutions across seven countries (United States of America (US), Switzerland, Netherlands, Germany, UK, Israel, Japan). DRLs (75th percentile) and median doses for volumetric CT-dose index (CTDI_vol) and dose-length product (DLP) were assessed for each EUCLID category (chronic sinusitis, stroke, cervical spine trauma, coronary calcium scoring, lung cancer, pulmonary embolism, coronary CT angiography, hepatocellular carcinoma (HCC), colic/abdominal pain, appendicitis), and US radiation doses were compared with European.

Results

The number of CT scans within EUCLID categories ranged from 8,933 (HCC) to over 1.2 million (stroke). There was greater variation in dose between categories than within categories (p < .001), and doses were significantly different between categories within anatomic areas. DRLs and median doses were assessed for all categories. DRLs were higher in the US for 9 of the 10 indications (except chronic sinusitis) than in Europe but with a significantly higher sample size in the US.

Conclusions

DRLs for CTDI_vol and DLP for EUCLID clinical indications from diverse organizations were established and can contribute to dose optimization. These values were usually significantly higher in the US than in Europe.

Key points

• Registry data were used to create benchmarks for 10 common indications for CT identified by the European Society of Radiology. • Observed US radiation doses were higher than European for 9 of 10 indications (except chronic sinusitis). • The presented diagnostic reference levels and median doses highlight potentially unnecessary variation in radiation dose.