Cancers of the Oral Cavity and Oropharynx: FDG PET with Contrast-enhanced CT in the Posttreatment Setting

Abstract

The combined use of fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) and contrast material-enhanced computed tomography (CT) for posttreatment monitoring of cancers of the oral cavity and oropharynx has steadily increased in recent years. FDG PET/CT offers many advantages for evaluating the effects of therapy, determining whether residual or recurrent disease is present, and assessing the extent of nodal disease. Because of the high negative predictive value of this imaging test, some have advocated the deferral of neck dissection in patients with negative findings at FDG PET/CT after chemotherapy and radiation therapy; positive findings may have a similarly heavy influence on the future course of treatment. Thus, the accuracy of image interpretation is crucial. However, the interpretation of posttreatment FDG PET images is challenging, with multiple potential pitfalls and limitations that could lead to an incorrect analysis. Accuracy depends on a detailed knowledge of the patient's treatment history and a thorough understanding of the kinds of changes that might result from treatment. Awareness of the principles underlying the selection of the optimal interval between the completion of treatment and the first follow-up FDG PET/CT examination is especially important, since an interval that is too short could lead to false-positive or false-negative findings. A period of 12 weeks or more is generally recommended, but the optimal waiting period depends on the extent of therapy and other factors. If recurrence or progression is suspected during the waiting period, contrast-enhanced CT or magnetic resonance imaging should be performed without FDG PET.

Loco-regional recurrence after surgical treatment of oral squamous cell carcinoma: Proposals for follow-up imaging based on literature, national guidelines and institutional experience

“…We suggest 3-monthly screening within the first 2 years with the above-mentioned algorithms, since most of the recurrences occur within this time interval. In contrast to Rivelli et al and King et al, we prefer the more closely spaced use of imaging because of the risk of recurrence in deep tissue; this is difficult to detect by palpation (King et al, 2011;Rivelli et al, 2011).…”

“…With regard to PET imaging, a waiting period of 12 weeks or more, depending on the extent of therapy, is recommended to avoid false-positive results (King et al, 2011). Within this protocol, the patient has the chance either of being spared an unnecessary additional salvage therapy or of receiving suitable salvage therapy within 12 weeks after the first surgical resection.…”

“…Although Rivelli et al and King et al suggest surveillance for much longer than 5 years in order to detect late-recurrent disease (King et al, 2011;Rivelli et al, 2011), other reports have shown that patients screened by routine follow-up for more than 5 years experience the same mean disease-free survival time after treatment as those controlled by self-initiated visits (Merkx et al, 2006;Mücke et al, 2009). Another important point is the possible existence of metachronic disease within the aerodigestive or pulmonary compartments in 4%e33% of patients with OSCC.…”

“…With an imaging time of 3e5 min for every MRI sequence, this can lead to substantial motion artefacts, whereas CT is usually performed within a few seconds. (King et al, 2011). An 18 F-FDG PET/CT-based follow-up at 12 months after primary surgical treatment of OSCC was found to be more accurate compared with physical examination alone in a follow-up of 91 patients with no clinical evidence of recurrence.…”

Radiographic Imaging of Human Papillomavirus Related Carcinomas of the Oropharynx

“…False positive results in PET-CECT can result from fasciculation in the flaps; aspiration or fungal pneumonia; fibrosis; and misinterpretation of normal activity in Waldeyer's ring, muscle, mucosa and salivary tissue. Symmetry is not only lost with respect to architecture of the neck in the post-treatment patient, but also lost with respect to metabolic activity; tissue damage by radiation reduces background physiologic activity on the affected side [27].…”