Mesorectal node metastasis from gynecological cancer in the era of 3D conformal pelvic radiation therapy and intensity modulated radiation therapy

Whole pelvic radiation therapy (WPRT) is an integral part of treatment for locally advanced cervical and vaginal cancer prior to brachytherapy. The most common beam arrangements for WPRT are opposed anteroposterior/ posteroanterior beams and the 4-field box. The lateral fields of the 4-field box spare small bowel and a portion of the rectum from radiation. Intensity modulated radiation therapy (IMRT) is increasingly used for gynecologic (GYN) cancers to improve dose conformity. Before the availability of computed tomography (CT), the portals used for WPRTwere determined solely based on bony anatomy. Because fluoroscopy-based planning risks geometric miss,1,2 CT-based planning is now considered standard. Conventional WPRT portals are designed to include the primary tumor, uterus, upper vagina, and regional lymphatics (common, external and internal iliac, and presacral lymph nodes). However, the mesorectum is not consistently contoured as a target volume. The advent of fluorine-18 fludeoxyglucose (FDG) positron emission tomography (PET)/CT scan has increased