Suresh Mukherji

CT perfusion provides the unique ability to noninvasively quantify the microvascular blood flow of tumors and normal tissues. CTP provides important information on the biologic response to nonsurgical organ preservation and has the potential to determine whether the tumor is properly responding to nonsurgical organ preservation therapy (NSOPT). The ability to noninvasively monitor tumor response during NSOPT is the “Holy Grail” of cancer treatment. Accurate identification of nonresponding tumors would permit early implementation of adaptive radiotherapy, adjuvant chemotherapy, or surgical resection. The results of discovering the “Holy Grail” would have widespread implications and increase patient survival, create a rational approach for implementation of costly new chemotherapy agents, and help reduce the growing costs of salvage therapy and end-of-life care.

The initial results investigating the role of CTP for monitoring response to NSOPT are promising. These results suggest that changes in CTP have the ability to noninvasively predict response to NSOPT.  Several of the most important articles published in the AJNR are provided in this digest. There is also early evidence to suggest that CTP is correlated with molecular

biomarkers that may increase the efficacy of targeted chemotherapy. One of the papers in this digest reports new data suggesting that CTP is predictive of the expression of the epidermal growth factor receptor (EGFR), which is the mechanism of the drug cetuximab.

The initial results are promising, but there still remain more questions than answers. Such questions include: When is the optimal time to perform biologic imaging for treatment monitoring? Should CTP be performed early and often during the course of disease, or should it be performed at the point of maximum treatment effect, when adjuvant therapy can still be effective? Which CTP parameter is most predictive? The early data show that the CTP parameters vary during the course of treatment, but blood flow and blood volume tend to be reduced in responders after approximately 4000 Gy. However, there is no clear consensus, and more investigations need to be performed.

The most encouraging aspect of such investigations is that there is now consensus among radiation oncologists that biologic imaging response precedes changes in tumor volume for predicting response. Thus, the time is ripe for collaborative interdisciplinary investigations. This AJNR Digest lists some of the most promising articles investigating the role of CTP for monitoring treatment response. My hope is that this digest will promote future collaborative investigations, as I am confident that adaptive therapy one day will be based on biologic imaging response (as opposed to changes in tumor size), which will result in increased cancer survival.

Image modified from: Bisdas S, Rumboldt Z, Šurlan-Popovič, et al. Perfusion CT in Squamous Cell Carcinoma of the Upper Aerodigestive Tract: Long-Term Predictive Value of Baseline Perfusion CT Measurements