Somatostatin receptor PET/CT

A report skeleton for 68Ga-DOTATATE, 68Ga-DOTATOC or 64Cu-DOTATATE PET/CT in neuroendocrine tumours. It follows the SNMMI/EANM 2023 procedure standard, grades uptake with the modified Krenning score, categorises lesions with SSTR-RADS 1.0, and ends with a PRRT eligibility statement.

Based on: SNMMI procedure standard/EANM practice guideline for SSTR PET (Hope 2023); SSTR-RADS 1.0 (Werner 2018); NANETS/SNMMI PRRT procedure standard (Hope 2019)

SOMATOSTATIN RECEPTOR PET/CT

CLINICAL INDICATION:
  [Staging / restaging / suspected primary / assessment for PRRT / response assessment]
  Histology: [site, WHO grade, Ki-67 [ ]%]; functioning syndrome: [ ]
  Somatostatin analogue: [none / short-acting, last dose [ ] h ago / long-acting [octreotide LAR / lanreotide], last dose [date]]
  Prior PRRT / surgery / liver-directed therapy: [ ]

TECHNIQUE:
  Radiopharmaceutical: [68Ga-DOTATATE / 68Ga-DOTATOC / 64Cu-DOTATATE] [ ] MBq IV at [time], [site]
  Uptake time: [ ] min (68Ga-DOTATATE 40–90 min; 68Ga-DOTATOC 55–90 min; 64Cu-DOTATATE 45–90 min)
  Coverage: [skull base / vertex] to [mid-thigh]; CT: [low-dose / diagnostic contrast-enhanced]

COMPARISON:
  [Prior SSTR PET / FDG PET / CT / MRI dated [ ] / none]

FINDINGS:
  Reference uptake: liver SUVmax [ ]; spleen SUVmax [ ]
  Primary tumour: [site, size, SUVmax, Krenning score]
  Lymph nodes: [ ]
  Liver: [number / distribution, dominant lesion SUVmax]
  Bone: [ ]
  Other sites: [ ]
  Lesions with CT or MRI abnormality but little or no SSTR expression: [none / [site, size]]
  Physiological uptake and pitfalls considered: [uncinate process, splenules, adrenals, pituitary, degenerative bone, inflammation]

MODIFIED KRENNING SCORE (lesion with the highest uptake):
  0 = no uptake
  1 = very low uptake
  2 = uptake less than or equal to liver
  3 = uptake greater than liver
  4 = uptake greater than spleen

SSTR-RADS 1.0 (per target lesion; the highest category gives the overall score):
  1 = definitively benign (1A normal biodistribution; 1B benign lesion with discernible uptake)
  2 = likely benign (low or nonspecific uptake at a site atypical for NET)
  3A = equivocal soft tissue (low uptake at a site typical for NET)
  3B = equivocal bone (low uptake in a bone lesion not atypical for NET)
  3C = intense uptake at a site highly atypical for NET (consider another tumour)
  3D = lesion very likely malignant on anatomical imaging but without SSTR uptake
  4 = intense uptake at a site typical for NET without a corresponding finding on anatomical imaging
  5 = intense uptake at a site typical for NET with a corresponding anatomical finding
  Overall SSTR-RADS: [ ]

IMPRESSION:
  1. [SSTR-expressing disease at [sites] / no SSTR-expressing disease]
  2. Highest modified Krenning score [ ]; overall SSTR-RADS [ ]
  3. PRRT: [SSTR expression greater than liver in the known disease, SSTR-RADS 4–5, supports eligibility for PRRT / insufficient uptake or SSTR-negative disease (3D) at [site], so PRRT is not supported on imaging / not assessed]
  4. [Recommendation, e.g. FDG PET/CT for SSTR-negative disease, biopsy]

Before you sign

• Record the timing of the last somatostatin analogue. Stop short-acting analogues 12 h before the scan. For long-acting analogues, image 3–4 weeks after the last dose, ideally just before the next one.
• Base the modified Krenning score on the lesion with the highest uptake and quote liver and spleen as references. Higher uptake predicts a better response to PRRT.
• For PRRT, lesion uptake should exceed background liver uptake. Give an overall SSTR-RADS 4 or 5 and PRRT should be considered.
• Any lesion that is suspicious on CT or MRI but SSTR-negative (SSTR-RADS 3D) must be listed. It may mean dedifferentiated disease that PRRT will not treat, and FDG PET can be considered.
• Uptake in the uncinate process or head of pancreas is often physiological, and splenules, including intrapancreatic ones, take up as much tracer as spleen. Other false positives are degenerative bone, fractures, fibrous dysplasia, radiation change and reactive nodes, including sarcoidosis.
• If there are more than five lesions, SSTR-RADS scores a dominant, representative lesion in each system. The highest category gives the overall score.
• SUVs may not be reproducible across scanners and institutions without standardisation, so interpret changes in absolute SUV with care. Tumour-to-liver ratios are an alternative measure.

Sources

1. Hope TA, Allen-Auerbach M, Bodei L, et al. SNMMI procedure standard/EANM practice guideline for SSTR PET: imaging neuroendocrine tumors. J Nucl Med. 2023;64:204–10.
2. Werner RA, Solnes LB, Javadi MS, et al. SSTR-RADS version 1.0 as a reporting system for SSTR PET imaging and selection of potential PRRT candidates: a proposed standardization framework. J Nucl Med. 2018;59:1085–91.
3. Hope TA, Abbott A, Colucci K, et al. NANETS/SNMMI procedure standard for somatostatin receptor-based peptide receptor radionuclide therapy with ¹⁷⁷Lu-DOTATATE. J Nucl Med. 2019;60:937–43.