PET/CT for the staging and follow-up of patients with malignancies
Introduction
In patients with suspected malignancies both prognosis and therapeutic management particularly depend on the tumour stage. Thus, accurate tumour staging preferably encompassing the entire body is of high importance.
PET is a very sensitive modality to depict the spatial whole-body distribution of positron-emitting biomarkers that indicate molecular processes underlying tumour metabolic activity [1]. The average F-18-FDG PET sensitivity and specificity across all indications in oncology are estimated at 84% (based on 18,402 patient studies) and 88% (based on 14,264 patient studies), respectively, according to Gambhir et al. [2] from a collection of 419 articles from 1993 to 2000.
However, sole PET images are lacking detailed anatomical information. Reliable localisation of a lesion within a segment of an organ or even within a certain organ itself can be challenging. Thus, conventional stand-alone PET has mostly been replaced by PET/CT. PET/CT combines the complementary information of functional PET and morphological CT images in one imaging session for improved patient comfort, patient throughput, and most importantly the gain in diagnostic accuracy. FDG-PET/CT has been found superior to both imaging procedures acquired separately in tumour staging and restaging of different malignant diseases [3], [4], [5]. Furthermore, PET/CT potentially supports volume delineation in radiation therapy planning [6]. This may be particularly useful in the head and neck region where a multitude of sensitive structures is confined to a small area of the body. The close vicinity necessitates optimised definition of the treatment volume to minimise the risk of treatment-related toxicities. Another indication for PET/CT in radiation therapy planning is lung tumours where separation of viable tumour from atelectasis can be challenging with morphology alone [6].
While PET imaging has been available since 1980, PET/CT has first been introduced into clinical routine in 2001. Thus, there are many data on PET in oncological applications available in the literature, while data on PET/CT are still limited for some tumour entities. However, depending on the indication and the radionuclide in question data on PET imaging may in all likelihood also apply to PET/CT.
This review will (1) cover methodological issues in PET/CT and (2) focus on the main oncological indications of FDG-PET/CT.
Section snippets
Methodological and technical issues in PET/CT
Two separate scanners, a PET and a CT scanner, are installed in series with a single gantry and examination table serving both imaging devices. Prior to the examination a positron-emitting biomarker is administered. The examination is then performed by positioning the patient on the examination table followed by sequential acquisition of the CT and of the PET images. Both data sets can be combined into a single superposed (coregistered) image. Differences between PET/CT systems apply to the
General clinical issues in oncological FDG-PET/CT
The initiation of a stage-adapted therapy is known to improve outcome in various malignancies [21], [22]. In recent years, numerous studies have evaluated the use of FDG-PET for staging and restaging of tumour patients. The currently available data indicate that PET/CT is more accurate than either of its imaging components alone or if images are acquired with separate PET and CT systems and viewed side by side. PET and CT complement one another in fused PET/CT data sets. PET may be more
Concluding remarks and future perspectives
PET and CT complement each other's strengths in integrated PET/CT. Due to developments in system technology PET/CT devices are continually gaining spatial resolution and imaging speed. The standard whole-body imaging simplifies tumour staging and speeds up decision processes to determine appropriate therapeutic strategies. PET/CT proved to be of high value as the primary staging and restaging modality in many tumour entities. As PET/CT will be useful in all indications where PET proved to be
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