Perfusion CT helps predict lung cancer response
According to the authors, because of the relatively slow tumor shrinkage in various platinum-based chemotherapy regimens—as measured on CT images—a substantial percentage of patients may undergo several weeks of toxic therapy without benefits. However, response assessment with morphologic imaging techniques such as CT has limitations in reliable differentiation of necrotic tumor or fibrotic scar from residual tumor tissue.
Perfusion CT shows how much blood is present in the area being imaged and how quickly it is moving. It is performed by scanning a patient every few seconds before, during and after the intravenous delivery of a contrast agent. Perfusion scans can be made on most CT systems with the use of advanced visualization software.
A multinational team from Peking Union Medical College in Beijing and New York Presbyterian Medical Center in New York City initiated a prospective study to evaluate the feasibility of the technology for prediction of early tumor response and prognosis of NSCLC.
“The purpose of our study was to prospectively monitor changes in tumor perfusion after chemotherapy, radiation therapy, or both and to determine whether perfusion parameters can be used for prognosis and prediction of early tumor response to therapy for NSCLC,” they wrote.
Perfusion CT was performed with a 16-slice (LightSpeed Pro 16, GE Healthcare) or an 8-slice (LightSpeedUltra, GE) scanner. Of the 152 patients who consented to having perfusion CT, 123 had lung cancer pathologically proven with surgery, bronchoscopy, or biopsy. The images were processed using CT Perfusion 3 software, also from GE.
“Functional maps were generated with color scales based on the following perfusion parameters: blood flow per 100 grams of wet tissue per minute; blood volume per 100 grams of wet tissue; mean transit time of contrast material in the local vascular system; and permeability–surface area product, which is the rate of contrast leakage into the extracellular space,” the authors wrote.
A follow-up perfusion CT scan was obtained with the same protocol as the baseline perfusion CT scan after two-cycles of chemotherapy or before the end of radiation therapy. Tumor response to treatment was evaluated according to Response Evaluation Criteria In Solid Tumors (RECIST) criteria, including target lesions and non-target lesions at contrast-enhanced CT.
The quality of each functional map was rated from 0 to 3 for the 123 patients with confirmed lung cancer. A subset of images was independently reviewed by two radiologists to measure interobserver and intraobserver variability. Perfusion parameters and tumor response were assessed for 35 patients with NSCLC who underwent chemoradiation therapy. Progression-free survival and overall survival were analyzed for 22 patients who underwent repeated perfusion CT after therapy.
The researchers reported that the patients who responded to chemoradiation therapy had significantly greater blood flow than patients who did not respond. The median progression-free survival period of the patients with an increased permeability–surface area product was 4.7 months, significantly lower than the median progression-free survival period of 19 months among patients with a decreased permeability–surface area product.
The median overall survival period was 10.6 months for the group with an increased permeability–surface area product, significantly lower than the 19.3 months for the group with a decreased permeability–surface area product.
“Perfusion CT is useful in predicting early tumor response and the prognosis of NSCLC after chemoradiation therapy,” the authors concluded. “In the future, monitoring the response to therapy with perfusion CT may aid clinicians in customizing the treatment of each patient, improving patient selection for particular therapies, and avoiding nonproductive treatment regimens.”