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Before the advent of diagnostic imaging, nuclear medicine was a treatment modality. The first therapeutic application of radioisotopes was almost contemporaneous with the discovery of radioactivity. P-32 became one of the first effective therapies for a range of malignant blood disorders; I-131 was established as the benchmark for the treatment of metastatic thyroid cancer; Sr-89 was recognised to provide palliative benefit in advanced prostate cancer. The development of tomographic imaging with SPECT and PET, further enhanced by hybrid CT or MRI devices, has recently focussed the speciality of nuclear medicine on the diagnostic use of isotopes. Against this trend there has been renewed awareness on the ability of radiotracers to identify potential therapeutic targets and to use this information to select patients for and to monitor the efficacy of targeted therapies using radioisotopes. This process has been termed “theranostics”. A significant factor in the rebirth of therapeutic nuclear medicine has been the development of peptides labelled with Ga-68 and Lu-177. Ga-68 DOTA-octreotate PET/CT and Lu-177 DOTA-octreotate peptide receptor radionuclide therapy (PRRT) provides the modern prototype of the theranostic paradigm. Experience with PRRT has, however, emphasised the need for a more rigorous scientific approach to radionuclide therapy. The future holds promise of wide range of therapeutic options based on diagnostic/therapeutic pairs including I-124/I-131 and Cu-64/Cu-67. Quantitative SPECT/CT and PET/CT will be key platform technologies for planning and monitoring such therapy and will realise the true promise of molecular imaging in characterising rather than just finding disease.

With an increasing number of positron emission tomography (PET) facilities while a growing shortage of PET specialists in mainland China, interactive communication between PET specialists and oncologists plays a crucial role in individualized management of cancer patients and survivors. It is essential that PET specialists should be well informed by oncologists of their patients’ history, current problem, treatments, and particularly, the follow-up information. Vice versa, oncologists should be advised by PET specialists on their thorough interrogation, detailed observations, as well as potential false-positive or false-negative findings – some of which might be ignored in their reports. Improving communication and coordination between PET specialists and oncologists has been linked not only to greater understanding and cooperation but also better patient management. In addition, this interactive communication is an essential element of good collaboration for multicenter clinical trials, for instance, how to make PET as an imaging biomarker to evaluate efficacy more rapidly and to increase the probability of success in a clinical trial and how to move non-FDG radiopharmaceutical forward, etc. Here, our review focuses on the conceptual framework, key features, current problems, and future perspectives on this topic.

Positron emission tomography/computed tomography (PET/CT) using Ga-labelled DOTA-Tyr octreotide (DOTATOC) is one of the diagnostic imaging tools in somatostatin receptor scintigraphy. There have been many studies demonstrating the clinical usefulness of this diagnostic imaging method, especially for detecting neuroendocrine tumors (NETs). It often yields clinically relevant information for determining therapeutic management in NET patients. However, we have found that the usefulness of the information provided depends on the clinical situation; for example, it was considered especially helpful when recurrence/metastasis was suspected after surgery for histopathologically proven NET. In addition to NETs, DOTATOC PET/CT sometimes provides useful information in patients with tumor-induced osteomalacia (TIO), in which fibroblast growth factor 23 produced by a mesenchymal tumor causes hypophosphatemia, resulting in osteomalacia. As these mesenchymal tumors frequently express somatostatin receptors, DOTATOC PET/CT would be expected to detect causative lesions in TIO. Furthermore, many renal cell carcinomas (RCC) are not FDG avid. DOTATOC PET/CT could be helpful for detecting unexpected lesions when recurrence or metastasis is suspected after surgery for RCC. DOTATOC PET/CT is also able to reveal additional findings even in sarcoidosis, an inflammatory disease. The clinical value of DOTATOC PET/CT is discussed, based on our clinical experience.

: 4′-[methyl-C]-thiothymidine (4DST) has been developed as an in vivo cell proliferation marker based on the DNA incorporation method. We evaluated 4DST uptake on PET in patients with newly diagnosed and recurrent gliomas and correlated the results with proliferative activity.

: 4DST PET was investigated in 32 patients, including 21 with newly diagnosed gliomas and 11 with recurrent gliomas. PET imaging was performed at 15 min after 4DST injection. The standardized uptake value (SUV) was determined by region-of-interest analysis. The maximal SUV for tumor (T) and the mean SUV for contralateral normal brain tissue (N) were calculated and T/N ratio was determined. Proliferative activity as indicated by the Ki-67 index was estimated in tissue specimens.

: The sensitivity of 4DST PET for the detection of newly diagnosed and recurrent gliomas was 86 % and 100 %, respectively. In newly diagnosed gliomas, there was a weak correlation between T/N ratio and Ki-67 index ( = 0.45;  < 0.05). In recurrent gliomas, there was no significant difference between T/N ratio and Ki-67 index.

: In newly diagnosed gliomas, 4DST PET seems to be useful in the noninvasive assessment of proliferation.

Hypoxia is present in various solid tumors, including non-small cell lung cancer (NSCLC) and is associated with treatment resistance and poor prognosis. F-Fluoromisonidazole (FMISO) is a major PET tracer for hypoxia imaging. Previous studies have evaluated the potential role of FMISO-PET as a prognostic tool and assessed tumor reoxygenation following nonsurgical treatment in NSCLC. However, for cancers located in the thorax or abdomen, the patient’s breathing causes motion artifacts and misregistration between PET and CT images. PET/CT with the respiratory-gating technique improves the measurement of lesion uptake and tumor volume. We investigated the usefulness of respiratory gating for FMISO-PET/CT-based quantification of hypoxia. Among the 14 patients examined, hypoxia was observed in three patients with non-gated acquisition and in five patients with respiratory gating. The SUVmax, tumor-to-muscle ratio, tumor-to-blood ratio, and hypoxic volume were statistically significantly higher in respiratory-gated (RG) images than in non-respiratory-gated (NG) images. RG FMISO-PET/CT may be useful for the accurate quantification of hypoxia.