Utility of PET/CT Imaging Performed Early After Surgical Resection in the Adjuvant Treatment Planning for Head and Neck Cancer

Purpose

To evaluate the utility of positron emission tomography (PET)/computed tomography (CT) early after surgical resection and before postoperative adjuvant radiation therapy.

Methods and Materials

We studied a prospective cohort of 91 consecutive patients referred for postoperative adjuvant radiation therapy after complete surgical resection. Tumor histologies included 62 squamous cell and 29 non–squamous cell cancers. Median time between surgery and postoperative PET/CT was 28 days (range, 13–75 days). Findings suspicious for persistent/recurrent cancer or distant metastasis were biopsied. Correlation was made with changes in patient care.

Results

Based on PET/CT findings, 24 patients (26.4%) underwent biopsy of suspicious sites. Three patients with suspicious findings did not undergo biopsy because the abnormalities were not easily accessible. Eleven (45.8%) biopsies were positive for cancer. Treatment was changed for 14 (15.4%) patients (11 positive biopsy and 3 nonbiopsied patients) as a result. Treatment changes included abandonment of radiation therapy and switching to palliative chemotherapy or hospice care (4), increasing the radiation therapy dose (6), extending the radiation therapy treatment volume and increasing the dose (1), additional surgery (2), and adding palliative chemotherapy to palliative radiation therapy (1). Treatment for recurrent cancer and primary skin cancer were significant predictors of having a biopsy-proven, treatment-changing positive PET/CT (p < 0.03).

Conclusions

Even with an expectedly high rate of false positive PET/CT scans in this early postoperative period, PET/CT changed patient management in a relatively large proportion of patients. PET/CT can be recommended in the postoperative, preradiation therapy setting with the understanding that treatment-altering PET/CT findings should be biopsied for confirmation.

Introduction

The risk of developing a local or regional recurrence (18–31%) or distant metastases (20–25%) remains relatively high despite aggressive multimodality postoperative adjuvant therapy for completely resected head and neck cancer 1, 2. One explanation for this may be clinically unidentified progression of persistent local or regional disease or distant metastases during the interval between surgery and the onset of postoperative adjuvant therapy because of rapid repopulation and proliferation of subclinical malignant clonogenic tumor cells. If such disease could be identified before the start of adjuvant therapy, subsequent therapy could be modified to improve tumor control and survival in the case of persistent or recurrent locoregional disease or avoid unnecessary toxicity and cost in the case of distant metastatic disease.

The diagnosis of recurrent or persistent head and neck cancer is a challenge in patients previously treated with surgery, radiation therapy, or both. Postoperative and postradiation tissue changes lead to unreliable detection by traditional methods of history, physical exam, computed tomography (CT), and magnetic resonance imaging.

By its ability to detect malignant hypermetabolic activity, positron emission tomography (PET) using ¹⁸F-fluoro-2-deoxyglucose (FDG) has been suggested to have significant advantages over traditional imaging modalities in identifying subclinical local or regional recurrent or persistent disease and distant metastases after surgery, radiation therapy, chemotherapy, or various combinations of these modalities 3, 4, 5, 6, 7, 8, 9, 10, 11.

The fusion of PET with CT (PET/CT) expands the benefits of either PET or CT alone by enhancing functional and anatomic relationships 12, 13. Hybrid PET/CT has been found to be more accurate than PET alone in the detection and anatomic localization of head and neck cancer, when study subjects had known or suspected disease 13, 14, 15. In a recent study, PET/CT had a small but distinct advantage over PET alone for surveillance of head and neck cancer (16). However, the question regarding the utility of PET/CT in the early postoperative restaging and adjuvant treatment planning of head and neck cancer has not been previously addressed.

Both PET alone and PET/CT have been thought to have limited ability to differentiate signals related to tumor, postoperative inflammation, or normal intense physiologic metabolic uptake in the head-and-neck region when performed in the early postoperative period. In a recent review of the literature, it was recommended that PET imaging be performed no sooner than 2 to 3 months after surgery ± chemoradiation therapy to reduce the incidence of false-positive results secondary to inflammation (8). This suggested interval would preclude the application of PET/CT for adjuvant therapy treatment planning during the time between surgery and the onset of adjuvant therapy, because adjuvant therapy is usually initiated 4 weeks after surgical resection.

In the present work, we evaluated how often a PET/CT, performed at a relatively early time point after curative-intent surgical resection and before planned postoperative adjuvant radiation therapy, identified biopsy-proven locoregional persistent or recurrent cancer or distant metastasis that resulted in changes in the treatment plan.