Impact of (18)F-FDG-PET/CT on staging and irradiation of patients with locally advanced rectal cancer.

Purpose: To investigate the impact of fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) on planning of neoadjuvant radiotherapy for locally advanced rectal cancer (LARC) patients. Patients and Methods: From January 2003 to December 2007, a total of 36 patients with LARC underwent a retroprospective PET/CT study for radiotherapy-planning purposes. Gross tumor volume (GTV), clinical target volume (CTV) and planning target volume (PTV) were defined in a retrospective analysis by a blinded reader. The hypothetical boost volume was defined primarily on CT alone, and afterwards on the fused PET/CT dataset. The CT- and PET/CT-based GTVs were quantitatively compared and percentage of overlap (OV%) was calculated and analyzed. The impact of PET/CT on radiation treatment planning and overall patient management was evaluated. Results: PET/CT-GTVs were smaller than CT-GTVs (p < 0.05). PET/CT imaging resulted in a change of overall management for three patients (8 %). In 16 of 35 patients (46 %), PET/CT resulted in a need for modification of the usual target volumes (CT-PTV) because of detection of a geographic miss. Conclusion: FDG-PET/CT had significant impact on radiotherapy planning and overall treatment of patients with LARC.