Cancer: PET/CT is sensitive for detecting recurrent head, neck cancer

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PET/CT is a highly sensitive technique for detecting recurrent head and neck cancer, according to a study in the Oct 1. issue of Cancer.

Johnny Kao, MD, from the department of radiation oncology at Mount Sinai School of Medicine in New York City, and colleagues, wrote that surgery and radiation therapy for head and neck cancer can distort head and neck anatomy, which can reduce the accuracy of follow-up physical exams, as well as CT and MRI.

The author said the goal of their study was to determine how diagnostically accurate follow-up PET/CT is in detecting locoregional recurrence, distant metastases and second primary tumors and to evaluate what kind of impact PET/CT could have on the prognosis and management of disease recurrence.

The authors looked at 80 consecutive patients with stage II through IV-B head and neck cancer who were treated with radiation therapy between July 2005 and August 2007. All patients were followed with a clinical exam, PET/CT and correlative imaging for a minimum of 11 months with a median follow-up period of 20.5 months.

A standard neck and head exam was performed in all patients during follow-up appointments at three-month intervals for the first two years, and at six month intervals after that. An initial PET/CT was recommended at two to four months after completion of radiation therapy and at four- to six-month intervals after that. The 80 patients received a total of 240 PET/CT scans on a GE Healthcare Discovery LS 16 PET/CT system.

Of the 240 PET/CT scans, 22 percent were interpreted as positive, according to the authors. The positive predictive value was 64 percent overall. The positive predictive values for local, regional and distant sites were 56 percent, 65 percent and 82 percent, respectively. Overall, the sensitivity, specificity and negative predictive value for PET/CT after radiation therapy were 94 percent, 90 percent and 99 percent, respectively.

Following PET/CT imaging, 34 patients underwent biopsy, including 19 patients with true-positive results, 10 patients with false-positive results and five patients with both false-positive and true-positive results. For the diagnosis of recurrent disease, the sensitivity, specificity, and positive and negative predictive values for follow-up PET/CT were 92 percent, 78 percent, and 59 percent and 96 percent, respectively.

Of 24 patients with recurrent or secondary primary tumors, only eight were suspected to have disease recurrence based on history and exam. The investigators reported that 13 patients had isolated failures or second primary tumors at distant sites that would not have been detected solely by CT. Two of nine patients with isolated locoregional disease recurrence had indeterminate CT scans. Twelve patients derived a potential benefit from early diagnosis.

According to the researchers, of the PET/CT studies performed within six months of completion of radiation therapy, 57 were negative and 22 positive. The negative PET/CT studies were associated with significantly improved two-year locoregional control (97 vs. 49 percent), distant control (95 vs. 46 percent), progression-free survival (93 vs. 30 percent) and overall survival (100 vs. 32 percent) compared with patients with positive PET/CT studies.

“PET/CT appears to be a highly sensitive technique for the detection of recurrent disease,” Kao and colleagues concluded. “Furthermore, negative PET/CT results within six months of the completion of radiation therapy offer significant prognostic value.”