Post-treatment imaging offers precise tracking of rectal cancer recurrence

Despite advances in the diagnosis and treatment of rectal cancer, five-year survival rates continue to hover around the 50% mark. For cancers limited to the bowel wall, however, the survival rate climbs to 83%, highlighting the importance of early detection and treatment. Almost all rectal cancers are primary adenocarcinomas, and 90% of them occur after the age of 50.

Rectal cancer is also likely to recur locally or to metastasize to the liver, lymph nodes, lung, and bones. To detect local recurrence or spread early, aggressive post-treatment follow-up with MR, CT, or, in limited cases, PET scanning, is necessary. High-resolution MR and CT can provide accurate evaluation of the extension of the tumor into the perirectal fascia and involvement of adjacent organs and lymph nodes.

New treatments, particularly total mesorectal excision (TME), often accompanied by radiation therapy, have reduced the incidence of recurrence considerably.

TME involves the complete excision of the lymphovascular package of the rectum surrounded by an intact mesorectal fascia. With this technique, local recurrence levels have been reduced to as low as 5% at some institutions.

Recurrence is less likely in patients with midrectal, upper rectal, and posterior cancers than in those with very low rectal cancers or anterior tumors. Patients with these higher risk tumors tend to benefit most from radiation therapy and usually need more aggressive post-treatment follow-up. In Europe, radiation therapy is typically ordered before surgery; in the U.S., it is more common after surgery.

While treatment for rectal cancer has become more standardized across Europe, variation exists in the post-treatment follow-up imaging protocols, said Prof. Dr. Thomas Vogl, a professor of radiology at the Diagnostic and Interventional Radiology Institutes in Frankfurt-am-Main, Germany.

"We need to become more standardized in our follow-up and develop a more exact time frame for determining how, when, and where patients should be followed up," he said.

As an advocate of Europe-wide guidelines for post-treatment imaging protocols for rectal cancer, Vogl has studied the various approaches used in different countries. CT is currently the most common post-treatment imaging modality. Although CT has good diagnostic accuracy, it is limited by problems with soft-tissue resolution. As reported at the ECR last year, CT has a sensitivity of 71% for detecting rectal cancer tumor invasion, compared with 84% sensitivity for MR. CT's specificity is 55%, against MR's 68%.

Post-treatment multislice CT scans should always be performed with contrast and 3D reconstruction, Vogl said. With MR, radiologists should follow high-resolution contrast-enhanced T2-weighted and T1 contrast-enhanced protocols.

"It's important to have an early post-treatment study, as soon as six to eight weeks after surgery or the last radiation therapy treatment," he said.

Early post-treatment studies can catch problems such as infection, abscess, and nerve injuries. Thereafter, MR scans should be performed every six months to detect scarring or recurrence. Dynamic and diffusion-weighted MR sequences can help distinguish between scarring and recurrent tumor. If local recurrence is detected, MR- or CT-guided biopsy should be ordered.

Detecting local recurrence and distant spread of cancer is important, but not all locally recurrent cancers need treatment. Patients with both locally recurrent disease and distant metastases may die before the locally recurrent disease becomes symptomatic.

For best results, radiologists, oncologists and other members of the medical team should work closely together, said Dr. Søren Rafaelsen, a radiologist at Vejle Hospital in Vejle, Denmark.