Radiotherapy is an effective treatment for treating metastatic disease. When used to treat disease in the lower abdomen or pelvis, however, it is frequently associated with gastrointestinal toxicity. The most common symptoms of radiation enteritis are diarrhea, bloating, and abdominal cramping. They are caused by irritation and inflammation of the bowel mucosa, and although the pathophysiology is poorly understood, it is thought to be due in part to malabsorption of bile salts and lactose, imbalances in bacterial flora, disturbances in motility. The true incidence of clinically significant enteritis is not well known and probably underestimated, because the majority of patients with symptoms do not seek medical advice, but is approximately 80% in patients receiving pelvic radiotherapy for gynecologic and rectal tumors. Different approaches have been taken to try to minimize acute small and large bowel toxicity from radiotherapy. Medical management with opioid derivatives, such as loperamide, is often effective for mild cases. Other medications, which try to inhibit the biochemical pathways leading to symptomatic gastroenteritis, have undergone clinical testing with some success. The other approach to minimizing toxicity is to minimize the volume and/or dose of radiation delivered to the small bowel. Simple mechanical devices, such as the "belly board" or a mesh sling, have had some success. With new techniques in intensity-modulated radiotherapy, it may be possible to avoid much of the bowel, or significantly reduce the dose delivered to the bowel, without mechanical intervention or compromising tumour doses. The aim of this trial is to test whether a new and highly sophisticated form of intensity modulated radiotherapy called helical tomotherapy can safely be used to deliver radiotherapy to the abdomen and pelvis. It will also establish whether this treatment modality will allow a reduction in the radiation dose to normal structures and the incidence of radiation-induced bowel injury. Helical tomotherapy is a new form of radiation treatment delivery which will be introduced at the Cross Cancer Institute in late 2001 or early 2002. Unlike standard radiotherapy, in which treatment is delivered through one or a few separate beams, helical tomotherapy delivers treatment with a rotating, intensity-modulated fan beam. The patient is translated through the ring of the gantry while the beam is rotated around, so that the treatment beam forms a helical shape in a similar manner to that of computed tomography (CT) scans. The ring gantry provides a stable platform to perform tomographic verification of both setup and delivered dose. Helical tomotherapy is similar to the NOMOS PeacockTM system currently in clinical use. The PeacockTM system also uses an intensity-modulated fan beam, but because it is an attachment to a standard C-arm linear accelerator, it delivers treatment by a "translate then rotate" method rather than a continuous spiral delivery. Because of the complete freedom of helical tomotherapy to deliver treatment from all angles around the patient and with intensity modulation and inverse treatment planning, it is possible to treat highly complex and irregular target volumes while giving a low radiation dose to surrounding normal structures. This study, along with a parallel study involving the treatment of bone metastases, will involve the first patients to be treated with helical tomotherapy at the Cross Cancer Institute. It will be an important first step in understanding the processes and capabilities of helical tomotherapy in delivering accurate image-guided therapy. It is designed to provide the framework for the next generation of clinical trials using helical tomotherapy in the adjuvant and radical setting. The objectives of the study are as follows: