Molecular imaging of cancer: evaluating characters of individual cancer by PET/SPECT imaging

Abstract

The present status of cancer molecular imaging (MI) with nuclear medicine techniques is reviewed, highlighting the Japanese activities in this field. With the progress in MI research, including significant contributions from Japanese studies, it has become possible to noninvasively evaluate various important characters of cancer in clinical patients, such as metabolism, cellular proliferation, tumor hypoxia, and receptor expression. Tumor metabolic information is used for tumor characterization, treatment response evaluation, and prognosis prediction. Hypoxia imaging is used for treatment planning and predicting treatment response. Receptor imaging can be used for the selection of the candidate for receptor-targeted treatment. Various novel probes that can target cancer-associated antigens, various cellular growth factor receptors, tumor angiogenesis, and so on, are under development, aiming for clinical evaluation. Application of radiolabeled ligands for treatment (targeted internal radiation therapy) is another important field in which MI technique can play a critical role. MI, which can deliver the outcome of basic oncological research to the bedside, is essential translational research for improved individualized patient management, and further advances in MI studies are eagerly awaited.

Figure 1

Met‐PET/CT (L‐[methyl‐¹¹C]methionine–positron emission tomography/computed tomography) of a recurrent rectal cancer patient treated with carbon ion radiotherapy (CIRT). Before CIRT, CT showed a recurrent tumor in the right pelvis (a: circle) and PET showed increased Met uptake in the tumor (b, c: arrow). Met‐PET/CT was repeated 1 month after CIRT. Although CT showed no significant change in tumor size (d: circle), Met uptake in the tumor was reduced significantly (e, f: arrow). Clinical follow‐up of this patient showed good local control.

Figure 2

FLT‐PET/CT (¹⁸F‐deoxy‐3′‐fluorothymidine–positron emission tomography/computed tomography) of a lung cancer patient treated with carbon ion radiotherapy (CIRT) (upper: PET images, lower: PET/CT fusion images). Before treatment, increased uptake of FLT was observed in the tumor (a: arrow). FLT‐PET/CT performed 2 days after CIRT showed significantly reduced tumor uptake of FLT, although the tumor size had not changed (b: arrow). FLT‐PET/CT obtained 3 months after treatment showed further reduction in FLT uptake accompanied by a decrease in tumor size (c: arrow).

Figure 3

Magentic resonance imaging (MRI), Met‐PET (L‐[methyl‐¹¹C]methionine–positron emission tomography), and ⁶²Cu‐ATSM‐PET (Cu‐diacetyl‐bis[N⁴‐methyl‐thiosemicarbazone]–PET) of a patient with uterine cervical cancer. T2‐weighted image shows an enlarged uterine cervix (a: arrow). Although strong uptake of Met (b: arrow) was observed, ⁶²Cu‐ATSM‐PET showed faint and very heterogeneous uptake of the tracer (c: arrow).

Figure 4

Two cases of gastrinoma. Case 1: somatostatin receptor scintigraphy (SRS) of a postoperative patient with gastrinoma shows multiple liver uptakes of ¹¹¹In‐DTPA‐octreotide corresponding to the known liver metastases (a: arrows). In addition, the posterior image of SRS shows focal uptake in the mid‐chest region (b: arrow). Bone scintigraphy obtained later showed the appearance of multiple bone metastases (c). Case 2: SRS of a patient with elevated serum gastrin level and no image evidence of responsible tumor showed a focal uptake near the upper pole of the right kidney (d: arrow). Abdominal SPECT (single‐photon emission computed tomography) showed that this uptake was located in the pancreatic head/duodenum region (e: arrow). Surgery confirmed the diagnosis of duodenal gastrinoma.

Figure 5

Schematic presentation of targeted imaging and therapy using radiolabeled ligands. PET/SPECT, positron emission tomography/single‐photon emission computed tomography.