This pilot study hypothesizes that hyperthermia delivered via magnetic resonance-guided focused ultrasound (MRg-FU) is technically feasible and can be safely used in combination with concurrent reirradiation and chemotherapy for the treatment of recurrent rectal cancer. Twenty recurrent rectal cancer patients who are not candidates for surgery will be recruited for hyperthermia treatment delivered via MRg-FU concurrent with reirradiation and oral chemotherapy.

Magnetic resonance-guided focused ultrasound (MRg-FU) is a non-invasive, outpatient modality being investigated for the thermal treatment of cancer. In MRg-FU, a specially designed transducer is used to focus a beam of low intensity ultrasound energy into a small volume at a specific target site in the body. MR is used to identify and delineate the tumour, focus the ultrasound beam on the target and provide real-time thermal mapping to ensure accurate heating of the designated target with minimal effect to the adjacent healthy tissue. The focused ultrasound beam produces therapeutic hyperthermia (40-42°C) in the target field causing protein denaturation and cell damage.

Currently, there is no prospective clinical data reported on the use of MRg-FU in the setting of recurrent rectal cancer. Recurrent rectal cancer is a vexing clinical problem. Current retreatment protocols have limited efficacy. The addition of hyperthermia to radiation and chemotherapy may enhance the therapeutic response. With recent advances in technology, the investigators hypothesize that MRg-FU is technically feasible and can be safely used in combination with concurrent reirradiation and chemotherapy for the treatment of recurrent rectal cancer without increased side-effects.

Inclusion Criteria:

• Able to give informed consent
• Weight <140kg
• Biopsy-proven recurrent rectal adenocarcinoma
• Assessed by the treating surgeon, medical oncologist and radiation oncologist, and following a multidisciplinary discussion, determined to have unresectable and/or inoperable disease in the presence or absence of distant metastases
• Assessed by the treating radiation oncologist and medical oncologist determined to be fit for reirradiation and chemotherapy
• Prior pelvic radiotherapy
• Target lesion visible by MR
• Target lesion accessible for MRg-FU procedure
• Target lesion maximum dimension ≤ 6cm
• Able to communicate sensation during MRg-FU treatment

Exclusion Criteria:

• Abdominal or pelvic surgery (excluding biopsy) ≤ 6 weeks prior to study enrolment
• Chemotherapy or other systemic anti-cancer agent ≤ 6 weeks prior to enrolment
• Previous radiotherapy ≤ 6 weeks prior to enrolment
• Recurrent tumour involves small bowel
• Unable to characterize pain
• Pregnant / Nursing woman
• Orthopaedic implant along proposed MRg-FU beam path or at site of target lesion.
• Serious cardiovascular, neurological, renal or hematological chronic disease
• Active infection
• Unable to tolerate required stationary position during treatment
• Allergy to MR contrast agent or sedation