MR-guided radiotherapy for rectal cancer

Colorectal cancer is the third most common cancer in the UK, with rectal cancer accounting for approximately 20-30% of all cases and men being affected more than women. Treatment of rectal cancer is not only to prevent disseminated disease, but to reduce the risk of local recurrence (LR). Unfortunately LR causes significant morbidity and distress […]Colorectal cancer is the third most common cancer in the UK, with rectal cancer accounting for approximately 20-30% of all cases and men being affected more than women. Treatment of rectal cancer is not only to prevent disseminated disease, but to reduce the risk of local recurrence (LR). Unfortunately LR causes significant morbidity and distress to patients, with symptoms of severe pain and anal sphincter incompetence leading to faecal incontinence, fistula formation and bleeding. Not only is this detrimental to physical health but mental health declines by means of social isolation due to the stigma associated with symptoms. Standard guidelines for treatment of rectal cancer is neoadjuvant chemoradiotherapy (nCRT) with Capecitabine to a total dose of 45Gy/25# followed by total mesorectal excision. Sequential phase two boosts of 5.4Gy-9Gy in 3-5# can be delivered to a smaller field to increase total dose in an attempt to achieve complete pathological response (cPR). Recent RCR guidelines have recommended that simultaneously integrated boost (SIB) via intensity modulated radiation therapy can also be delivered as long as image-guided radiotherapy is practised. Current radiotherapy planning protocols for rectal cancer include large population margins to incorporate systematic and random errors that occur due to geometric uncertainty in the target volume on CT. Dose delivered to the planning tumour volume (PTV) is therefore limited due to constraints set by the organs at risk.

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