Familial Nasopharyngeal Carcinoma 6

236 I. W. K. Tham and J. J. Lu17% and 14%, respectively, significantly lower thanthose of CT, which were 71% and 33%. MRI is alsomore sensitive than CT in detecting radiation-inducedcomplications including soft tissue changes, masticatormuscle fibrosis, arteriopathy, bone changes, centralnervous system, and cranial nerve palsies (Ng et al.1998). Nevertheless, it is limited in detecting earlymucosal recurrence and to differentiate local recurrencefrom immature fibrosis, edema, granulation, andinfection on the basis of MR signal intensity (Chongand Ong 2008).The value of FDG-PET or FDG-PET/CT in detectinglocal, regional, and/or distant metastases has been afocus of study recently. A recently published systemicreview (Liu et al. 2007) of 21 studies suggested that PETimaging was significantly more sensitive (95%) whencompared with CT (76%) or MRI (78%) in detectinglocally residual or recurrent tumor. A standard uptakevalues (SUV) cut-off of 4 at 3 months after completionof radiation therapy has been suggested as a diagnosticreference for recurrent or residual tumor (Yen et al.2006). FDG-PET is especially valuable in patients presentedwith equivocal results in follow-up MRI afterradiation treatment. In a study reported by Ng et al.(2004), 37 patients presented with questionable MRIfindings in the primary site underwent FDG-PET. Theresults of the study demonstrated that the sensitivity ofPET for detecting local, regional, and distant recurrencesreached 91.6 %, 90 %, and 100%, respectively;furthermore, the specificities for those recurrenceswere 76%, 89%, and 90.6%, respectively. Despite theadvantages of FDG-PET in detecting disease recurrencein NPC after definitive treatment, the high cost ofthe study at the present time prohibits many centersfrom using it routinely during follow-up. A cost–utilityanalysis in Taiwan (Yen et al. 2009) suggested that theuse of PET only if an MRI showed an uncertain resultprovided the most cost-effective solution for earlydetection of locoregional NPC recurrence. Therefore,PET or PET/CT can be recommended as a complementaryimaging modality to CT or MRI, rather than beingrelied on as the sole method of follow-up imaging inthe head and neck region (Ng et al. 2002).18.3.3Imaging for Distant MetastasesThe prevailing utilization of intensity-modulatedradiation therapy (IMRT) and concurrent chemoradiationtherapy for locoregionally advanced NPC hasassured improved local and regional control of thedisease. As such, distant recurrences have become amore predominant pattern of treatment failure fornon-metastatic NPC at diagnosis (Lee et al. 2002). Forpatients with locally advanced disease receivingchemoradiation therapy, the rate of distant metastasesmay range between 13% and 21% (Kwong et al. 2004;Wee et al. 2005). In addition, it has been estimated thatup to 54% of patients with local recurrence may harborsynchronous distant metastases (Lee et al. 1993).Although the disease could spread to any organ ortissue in the body, the most common sites for distantmetastatic NPC include bone, lung and liver (Al-Sarraf et al. 1998; Lee and Kong 2008). Detection ofmetastatic disease to these organs is largely throughimaging studies. Metastatic foci in the lung can bedetected by chest X-ray and/or CT of the thorax; livermetastases can be diagnosed by ultrasound and CT ofthe abdomen, and suspected bone metastases can beconfirmed by bone scan and/or X-ray.Recently published evidence suggests that PETscan or PET/CT is a sensitive modality for diagnosingrecurrences and metastases in NPC after definitivetherapy (Yen et al. 2005). The sensitivity,specificity, accuracy, positive and negative predictivevalue of FDG-PET images in the diagnosis of NPCrecurrence or metastases and secondary primarycancers were 92%, 90%, 92%, 90%, and 91%, respectively,in patients with suspected disease recurrence.Furthermore, patients with FDG hypermetabolismhad a poorer overall survival when compared withpatients without increased FDG uptake. Similarly, acomparison of various methods to stage distantmetastases showed that PET/CT was the most sensitive,specific, and accurate imaging modality whencompared with conventional work-up consisting ofchest X-ray, liver ultrasound, and skeletal scintigraphy,CT of the thorax, abdomen, and skeletal scintigraphy,and PET alone (Chua et al. 2009). The accuracyof FDG-PET or FDG-PET/CT for detecting distantmetastases both exceed 90%, substantially higherthan conventional work-up or CT with bone scan.However, a number of important issues must beaddressed before PET or PET/CT can be routinelyconsidered in follow-up after definitive treatment ofNPC. Firstly, although hematogenous spread is one ofthe most common modes of treatment failure in NPC,the prevalence of distant metastasis is relativelylow, especially in patients without cervical lymphadenopathy after definitive treatment (Lin et al. 2009).Although distant metastasis has been observed in upto 20% of patients with locoregionally advanced NPCafter chemoradiation therapy, a lower probability of