Advancing Techniques of Radiation Therapy for Rectal Cancer

Since the advent of radiation therapy for rectal cancer, there has been continual investigation of advancing technologies and techniques that allow for improved dose conformality to target structures while limiting irradiation of surrounding normal tissue. For locally advanced disease, intensity modulated and proton beam radiation therapy both provide more highly conformal treatment volumes that reduce dose to organs at risk, though the clinical benefit in terms of toxicity reduction is unclear. For early stage disease, endorectal contact therapy and high-dose rate brachytherapy may be a definitive treatment option for patients who are poor operative candidates or those with low-lying tumors that desire sphincter-preservation. Finally, there has been growing evidence that supports stereotactic body radiotherapy as a safe and effective salvage treatment for the minority of patients that locally recur following trimodality therapy for locally advanced disease. This review addresses these topics that remain areas of active clinical investigation.

Introduction

More than 40,000 individuals are diagnosed with rectal cancer in the United States each year with a mortality rate near 40%.¹ Surgery with or without chemoradiation therapy (CRT) is the primary treatment for these patients. Both local recurrence and distant metastasis are a major concern in rectal cancer, and each is associated with substantial morbidity and mortality.² Advancements in surgical technique and neoadjuvant therapies, however, have resulted in reduced local and distant recurrence, with subsequent improvement in overall survival over the past decade.1, 3

Since 2004, preoperative CRT followed by surgery and adjuvant chemotherapy remains the standard of care for locally advanced rectal cancer (cT3-4 or node-positive). The inclusion of CRT in addition to surgery results in improved local control and disease-free survival.4, 5Furthermore, preoperative CRT results in improved local control and toxicity profile compared with postoperative therapy, and it may allow for downstaging to facilitate a sphincter-sparing low anterior resection for a tumor that may otherwise require abdominoperineal resection.⁵