Head and neck squamous cell carcinoma (HNSCC) represents more than 90 percent of head and neck tumors and is one of the most frequent human neoplasms. During the last decades, radiotherapy has emerged as a standard treatment of HNSCC and the number of patients treated with this modality has continuously increased. Moreover, treatment schedules for radiotherapy have improved and require more preparation and are therefore more time consuming. Thus, waiting time prior to radiotherapy becomes a major concern in many countries with reported delays of 70 days or even more.Clinicians involved in treating HNSCC face the problem of rapidly growing tumors but despite significant progress in the understanding of these tumors, their development and progression remain currently unpredictible at the time of diagnosis. In a retrospective trial, Laccourreye et al. studied the time of progression of symptoms and signs (TPSS) before diagnosis and treatment in 966 HNSCC cases and showed that for a given tumor stage, the longer was the TPSS, the better were the vital prognosis, the local and lymph node control. But there is no clear definition of fast growing tumor, with objective measurement.

A CT-scan is perfomed at the time of diagnosis. Several weeks later, a second CT-scan is necessary for treatment planning in order to define the tumoral target volume. This necessity provides the opportunity to compare tumoral volumes on both exams, and thus to assess tumoral progression. In a pilot study conducted with Institut Gustave Roussy, the investigators studied retrospectively the tumor and loco-regional progression in the waiting time between diagnostic and treatment planning CT-scans in a cohort of patients with oropharyngeal squamous cell carcinoma, treated by radio(chemo)therapy between April 2005 and April 2007. The study demonstrated that 53% of the patients presented a tumoral progression of \> 50% within a mean waiting time of 42.1 +/- 15.7 days. The investigators consider this situation as regrettable, and prospective trials are clearly needed to determine clinical consequences of these findings.

The current project aims to study prospectively the loco-regional tumoral progression within the waiting time between diagnostic and treatment planning CT-scans in a cohort of patients with OPSCC. Patients with oropharyngeal primary squamous cell carcinoma elected for radiotherapy or radiochemotherapy with curative intent will be selected. Tumor volume, number and size of pathological cervical lymph nodes (small diameter \> 1 cm) will be assessed on diagnostic CT-scan (DiCT) and treatment planning CT-scan (RtCT) using the summation of areas technique (computerized delineation). Tumoral progression and tumor doubling time will be calculated based on DiCT and RtCT in order to define different tumoral kinetics patterns. Human papillomavirus (HPV) status will be assessed by polymerase chain reaction (PCR) and p16 immunohistochemistry. As primary objective, the investigators will study the tumoral kinetics patterns with disease free survival (DFS) and overall survival (OS) in patients with OPSCC in order to study their clinical signification \[time frame: 5 years\]. As secondary objectives, the investigators will correlate the tumoral kinetics patterns with HPV status of patients with OPSCC, and compare tumoural kinetics to proliferation markers (Ki67, mitotic index) in order to develop predictive markers of tumour progression for head and neck cancers. An other complementary objective will compare tumor kinetics patterns with endoscopic aspect (ulcerative versus exophytic)