Pelvic Radiation Therapy in Rectal Cancer: Technical Considerations.

Abstract

R adiation therapy has an integral role in the treatment of rectal cancer. After surgery for stages T3-4N0-2M0 or T1-4NI-2M0, adjuvant radiation therapy plus chemotherapy is standard treatment. ~'z In patients with locally advanced or unresectable disease, preoperative radiation therapy with or without chemotherapy is highly recommended. 3a More recently, radiation therapy has been used in patients with resectable disease with the goal of sphincter preservation. These conservative approaches include preoperative radiation therapy followed by a low anterior resection/coloanal anastomosis ~ and postoperative radiation therapy after a local excision, 6 The design and delivery of pelvic radiation therapy for rectal cancer requires a knowledge of the patterns of failure, anatomy and identification of pelvic structures, and radiobiological principles. Furthermore, the use of proper equipment, implementation of methods to decrease treatment-related toxicity, and a close collaboration with the physics and technology staff is essential. The biological mechanisms of acute and delayed toxicity as well as dietary interventions have been previously discussed. 7,~ This article is limited to the technical aspects of the design of pelvic radiation therapy for rectal cancer. The first section will focus on methods to decrease treatment-related toxicity. This will be followed by a discussion of the design of treatment fields for a variety of common clinical presentations. Finally, a caveat: Technique articles should be interpreted with caution. Radiation oncology, as with other medical specialties, is both an art and a science. Therefore, this review should serve as a guide rather than a "cookbook."