Perfusion CT measures angiogenic changes in rectal cancer

Researchers have long predicted that angiogenic processes could be used to diagnose cancers and demonstrate their responses to therapy. Dr. Giuseppe Petralia of the University of Milan presented evidence Friday at the ECR meeting showing that perfusion CT could be an appropriate vehicle for interrogating angiogenic processes associated with rectal cancer.

Petralia used dynamic CT to examine 41 patients with confirmed rectal cancer. All were evaluated to collect values for perfusion, and 19 underwent follow-up with imaging after neoadjuvant radiotherapy and chemotherapy.

Imaging was performed with a 16-slice CT scanner with 10-mm slices acquired at less than one second per scan and 40 mL/sec of contrast medium. Time-to-peak (TTP), positive enhancement integral, maximum slope of increase, maximum slope of decrease, blood flow, blood volume, mean transmit time (MTT), and permeability surface data were collected. Total scanning time was less than 10 minutes.

CT was chosen to measure angiogenesis for this application because it allows the clinician to perform real-time imaging and could be used to acquire tumor perfusion and morphologic data quickly and reliably, Petralia said. The concentration of contrast medium is linearly related to attenuation measured in Hounsfield units.

Compared with the normal rectal wall, average blood flow was higher in 69% of tumors and TTP was higher in 76% of tumors, according to Petralia. The permeability surface of cancers was more than 20 mL per minute per 100 gram in all patients. A significant correlation was founded between TTP and the pathologic vessel density. Conversely, the average MTT was lower in tumor than normal rectal wall.

The results from follow-up studies suggest that this protocol could be used to measure therapeutic response. A comparison of perfusion measures acquired before and after therapy showed that blood flow (p = 0.002) and blood volume (p = 0.009) both decreased significantly after therapy. Simultaneously, average MTT rose significantly (p = 0.004).

"We can say that tumor fusion can reliably measure tumor perfusion, and it will allow monitoring of the response to therapy with a reliable detection of functional and morphologic changes," he said.

The protocol also has the potential to guide dosage alterations during therapy, Petralia said.