Initial experience of FDG-PET/CT guided IMRT of head-and-neck carcinoma

Purpose: The purpose of this study is to evaluate the impact of ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) fused with planning computed tomography (CT) on tumor localization, which guided intensity-modulated radiotherapy (IMRT) of patients with head-and-neck carcinoma.

Methods and Materials: From October 2002 through April 2005, we performed FDG-PET/CT guided IMRT for 28 patients with head-and-neck carcinoma. Patients were immobilized with face masks that were attached with five fiducial markers. FDG-PET and planning CT scans were performed on the same flattop table in one session and were then fused. Target volumes and critical organs were contoured, and IMRT plans were generated based on the fused images.

Results: All 28 patients had abnormal increased uptake in FDG-PET/CT scans. PET/CT resulted in CT-based staging changes in 16 of 28 (57%) patients. PET/CT fusions were successfully performed and were found to be accurate with the use of the two commercial planning systems. Volume analysis revealed that the PET/CT-based gross target volumes (GTVs) were significantly different from those contoured from the CT scans alone in 14 of 16 patients. In addition, 16 of 28 patients who were followed for more than 6 months did not have any evidence of locoregional recurrence in the median time of 17 months.

Conclusion: Fused images were found to be useful to delineate GTV required in IMRT planning. PET/CT should be considered for both initial staging and treatment planning in patients with head-and-neck carcinoma.

Introduction

Current therapies for head-and-neck carcinomas typically involve surgical resection or radiation for early-stage disease, and a combination of surgery and radiation or chemoradiotherapy, or all three combined, for locally advanced stage disease. Accumulating evidence demonstrates that high-dose radiation (e.g., altered fractioned or accelerated radiation) improves local control of head-and-neck tumors (1, 2, 3). However, these high doses are associated with a significant increase in toxicity, which negatively impacts patient quality of life and treatment compliance. Recently, intensity-modulated radiotherapy (IMRT) has emerged. Through modulation of radiation beam intensities in large numbers of different fields, IMRT is able to deliver a high dose of radiation to the gross tumor planning target volume (PTV) and high-risk subclinical disease regions, while irradiation of surrounding critical tissue structures such as the parotid glands, spinal cord, mandible, orbits, optical chiasm, and brain is minimized (4, 5). Recent studies have demonstrated that IMRT improves locoregional control (6, 7, 8), reduces side effects such as xerostomia (9), and improves quality of life (10). The Radiation Therapy Oncology Group (RTOG) is currently investigating the efficacy of IMRT in treating early-stage oropharyngeal carcinoma (RTOG H0022) and nasopharyngeal carcinoma (RTOG H0225). The patient accrual of RTOG H0022 has just been completed.

Because of the steep dose gradient with IMRT, accurate delineation of targets and critical structures is one of the key factors to clinical success with this technology. Traditionally, computed tomography (CT) has been used for staging and radiation treatment planning. Unfortunately, CT alone is not sufficient for tumor definition in many situations. For example, small primary tumors and normal size adenopathy are poorly defined or not identifiable on the CT. Frequently, enlarged inflammatory lymph nodes are often mistaken for adenopathy. The shortcomings of these imaging modalities potentially have a negative effect on accurate tumor targeting and clinical outcomes of radiotherapy. Recent studies have shown that ¹⁸F-fluorodeoxyglucose ([F-18] FDG) positron emission tomography (PET) is superior to CT in identifying primary lesions, lymph node involvement, and metastases or disease recurrence in patients with head-and-neck cancer (11, 12, 13). These advantages with PET are further enhanced by the recent availability of integrated PET/CT scanning, which provides combined anatomic and functional images (14). With the integrated system, the characterization and localization of a tumor and its extent are performed in a single imaging procedure. It is hypothesized that the application of integrated FDG-PET/CT technology in the advanced radiotherapy planning, especially IMRT, will improve target localization and improve conformal treatment.

The purpose of this study was to evaluate the feasibility of fusing FDG-PET with radiotherapy planning CT with the goal of enhancing tumor localization for IMRT, so that the tumor coverage and normal tissue sparing can be optimized in radiotherapy of head-and-neck cancer. We implemented FDG-PET/CT for IMRT of 28 patients with head-and-neck carcinoma. Initial clinical outcomes of these patients are reported.