AR: Perfusion CT may help predict response to therapy for rectal cancer patients
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Baseline perfusion CT imaging parameters, specifically blood flow and mean transit time, discriminated patients with rectal cancer who had a favorable response to chemoradiation therapy from those who did not, according to a study published in the February issue of Academic Radiology.

As the management of patients with rectal cancer has shifted toward chemoradiation therapy, physicians have been challenged to predict which tumors will respond to treatment as morphological criteria have been unreliable.

Luís Curvo-Semedo, MD, from the Universitary Clinic of Radiology at Coimbra University Hospitals in Coimbra, Portugal, and colleagues designed a prospective study to evaluate perfusion CT to assess changes in tumor vascularity after chemoradiation therapy and analyze the correlation between baseline parameters and tumor response.

The study population included 20 patients with biopsy-proven, locally advanced rectal cancer to be treated with chemoradiation therapy followed by surgical resection between November 2007 and September 2010.

Eleven of the 20 patients underwent a second CT prior to surgery. For each CT perfusion study, a radiologist and senior radiology resident determined blood flow (BF), blood volume (BV), mean transit time (MTT) and permeability-surface area product (PS). Correlation between the readers’ measurements was excellent for pre-chemoradiation therapy images and good to excellent for post-chemoradiation therapy measurements, according to Curvo-Semedo et al.

Histopathological findings showed 15 nonresponders and five responders to chemoradiation therapy.

Median baseline regions of interest were not significantly different between tumors that responded well and those that did not. However, there were significant differences in two perfusion parameters—BF and MTT. “BF was significantly lower and MTT was significantly higher in responders than in nonresponders…and were accurate for predicting a favorable tumor response to chemoradiation therapy,” wrote Curvo-Semedo and colleagues.

The researchers observed that median variation rates of perfusion parameters did not change significantly after chemoradiation therapy between responders and nonresponders, leading them to suggest that a baseline CT perfusion study could suffice to discriminate responders from nonresponders.

Curvo-Semedo et al acknowledged the limitations of the study, noting its small, single-site design, and added that the study could spur larger, multicenter trials.

The researchers summed, “[Both] parameters can accurately discriminate patients with a favorable response from the ones that fail to respond to preoperative chemoradiation therapy, potentially selecting high-risk patients with radio- and chemo-resistant tumors that may benefit from a more aggressive preoperative treatment approach.”