PET-CT fusion in radiation management of patients with anorectal tumors

Purpose To compare computed tomography (CT) with positron emission tomography–CT (PET-CT) scans with respect to anorectal tumor volumes, correlation in overlap, and influence on radiation treatment fields and patient care. Patients and Methods From March to November 2003, 20 patients with rectal cancer and 3 patients with anal cancer were treated with preoperative or definitive chemoradiation, respectively. Computed tomography simulation data generated a CT gross tumor volume (CT-GTV) and CT planning target volume (CT-PTV) and 18 F-fluoro-2-deoxy-glucose PET (FDG-PET) created a PET-GTV and PET-PTV. The PET-CT and CT images were fused using manual coregistration. Patients were treated with three-dimensional conformal therapy to traditional doses. The PET, CT, and overlap volumes (OVs) were measured in cubic centimeters. Results Mean PET-GTV was smaller than the mean CT-GTV (91.7 vs. 99.6 cm 3 ). The mean OV was 46.7%. As tumor volume increased, PET and CT OV correlated significantly ( p 10 and the posttreatment PET standardized uptake value was p = 0.047). Conclusions Variation in volume was significant, with 17% and 26% of patients requiring a change in treatment fields and patient management, respectively. Positron emission tomography can change the management for anorectal tumors by early detection of metastatic disease or disease outside standard radiation fields.