A quantitative comparison of gross tumor volumes delineated on [18F]-FDG-PET/CT scan and contrast-enhanced computed tomography scan in locally advanced head and neck carcinoma treated with Intensity Modulated Radiotherapy

Abstract

<p>Accurate tumor diagnosis is important in highly conformal techniques such as Intensity Modulated Radiotherapy (IMRT), which aims for high therapeutic ratio. We compared Gross Tumor Volume (GTV) (primary and nodal) delineated on <sup>18</sup>F-fluorodeoxyglucose positron emission tomography ([<sup>18</sup>F]-FDG-PET) scan to those delineated on contrast-enhanced computed tomography (CECT) scan and its impact on staging treated by IMRT.<strong> </strong>A total of 30 consecutive patients with locally advanced squamous cell carcinoma of head and neck were included in this study. FDG-PET and CECT scans were performed with dedicated positron emission tomography–computed tomography (PET/CT) scanner in a single session as part of radiotherapy treatment planning for IMRT. After treatment with concurrent chemoradiotherapy, all patients were followed for one year. Three out of 30 patients were excluded from the final analysis, as there was complete remission in PET/CT after neoadjuvant chemotherapy. For remaining 27 cases, the primary sites were 17 oropharynx, 2 hypopharynx, 7 larynx and 1 unknown primary with secondary neck node. PET–CT resulted in changes of CT-based staging in 25% patients (up-staged in 3 and down-staged in 4). GTV delineated on PET vs CT scan was GTV-PET (primary) of 20.15 cm<sup>3</sup> vs GTV-CT (primary) of 18.75 cm<sup>3</sup>, <em>p</em> = 0.803; and GTV-PET (nodes) of 28.45 cm<sup>3</sup> vs GTV-CT (nodes) of 21.56 cm<sup>3</sup>, <em>p</em> = 0.589. The mismatch between two target volumes was statistically insignificant (<em>p</em> = 0.635 for GTV primary, <em>p</em> = 0.187 for nodes). The mean GTV-PET outside CT for primary was 5.83 cm<sup>3</sup>, and for node was 8.47 cm<sup>3</sup>. Median follow-up was 12 months. One-year loco-regional control was 92%. The target delineation of GTV can be improved with functional imaging [<sup>18</sup>F]-FDG-PET/CT.</p>