T. Niazi

Radiation Therapy in the Treatment of Rectal Cancer

Over the last two decades, radiation treatment has evolved significantly, not only through its application in serial randomized clinical trials, but in the following aspects: Modern imaging, such as computerized CT scans and magnetic resonance imaging, is now an essential component in the determination of treatment strategies. In the era of Total Mesorectal excision surgery, pre-operative RT reduces local recurrence and can be given either with long course RT with 5 Fu based regimen or SCRT. For patients with positive CRM, tumor down staging is highly desirable and SCRT is not as effective to prevent local recurrence. Contemporary pattern of recurrence suggests that it is possible to lower the upper limit of the treatment field level. In an effort to reduce radiation related toxicity, field adjustments along with exploration of new radiation targeted radiation modalities are desirable.

Diagnosis and Treatment of Rectal Cancer

Carcinoma of the rectum, a common malignancy in developed countries, accounts for approximately one third of colorectal cancers. Although majority of the localized rectal cancers are potentially curable, local recurrence remains a serious problem with severe disability and impaired quality of life. Rectal cancer, which was a surgically-managed tumour, now requires the coordinated efforts of multidisciplinary team, colorectal surgery, radiation oncology, medical oncology, radiology and others. In addition to the staging workup, pre-treatment evaluation of the local disease, by endorectal ultrasound (EUS) and multislice computer tomography (CT) and magnetic resonance imaging (MRI), is utmost important to determine the surgical approach and the need for the various other treatment modalities: radiation and chemotherapy (ChT). The introduction of Total Mesorectal Excision (TME) and neoadjuvant Radiation Therapy (RT) have led to significant improvement in the loco-regional control of the rectal cancer, 90–94%. TME is now widely accepted as the standard surgical technique for rectal cancer. Local recurrence rates have been shown to decrease significantly with TME alone. However, the addition of radiation therapy has furthered this improvement, especially in patients having a circumferential resection margin (CRM) that is involved with tumour on pre-operative imaging. There are two radiation modalities used in the treatment of patients with solid tumours, external beam radiation (EBRT) and brachytherapy (BT). In rectal cancer EBRT is primarily used to optimize the rate of local control achieved by surgery. Numerous clinical trials have confirmed its benefit, with or without chemotherapy, in improving local control. However, the survival advantage and the impact on distant metastasis are controversial. In view of normal organ toxicity associated with EBRT, newer radiation delivery techniques have been explored. High dose rate brachytherapy (HDRB) delivers radiation by an endoluminal approach, avoiding the delivery through other organs, and as such, decreases normal organ toxicity. The emerging prospective data are very promising and an international phase III study is being conducted. Despite significant improvement in local control, over the last decade, one third of the patients continue to fail at distance, with metastases. The role of chemotherapy in conjunction with radiation therapy as a neo-adjuvant modality to TME has been, mostly, accepted as routine in North America. However, to date, evidence from Phase III-randomized studies in rectal cancer fails to demonstrate any benefit from additional post-operative adjuvant 5-fluorouracil (FU)-based chemotherapy in terms of disease-free or overall survival in locally advanced rectal cancer. There have been significant achievements in the treatment of rectal cancer over the past decade with multidisciplinary approach becoming the standard of care. Such approach allows for the selection of those patients who are cured with surgery alone, as well as those at risk for failing locally, thus achieving a balance between treatment toxicity risks and tumour control gains.