Treatment Monitoring with FDG PET/(CT)
The cover story in this issue discusses the role of PET imaging for assessing therapeutic responses in cancer. Over the past 15 years, a large body of evidence has demonstrated that FDG-PET imaging is uniquely useful to assess treatment responses in cancer patients.
Importantly, this can be accomplished early in the course of therapy when there is still an opportunity to change the patient management strategy. This is relevant since many chemo- and chemo/radiation treatments are only marginally effective, are associated with severe side effects and also can be very expensive. Early identification of treatment responses would thus enable referring physicians to optimize and individualize cancer treatments.
Reliable early response assessments have been demonstrated in lung cancer, lymphoma, breast cancer, esophageal cancer and colorectal cancer, among others. Previous evidence has shown that responding tumors are characterized by early reductions in FDG uptake by approximately 30 percent (for instance, after a single cycle of chemotherapy) and by approximately 60 percent at the end of treatment. Remarkably, these changes are seen across most tumors and across various types of chemotherapy. These observations are not limited to patients who undergo cytotoxic treatments but also are seen in those who receive cytostatic therapies.
These “thresholds” are consistent with the EORTC guidelines dating back more than 10 years and with the recently published PERCIST criteria. There are, however, limitations to applying these thresholds. Nevertheless, there are substantially more data to support the clinical use of these criteria when compared with the CT-based response criteria.
This prompts the question: Why is the adoption of the PET-based approach so slow? First, RECIST has been used for decades and practice patterns are difficult to change. Second, RECIST, while inaccurate, provides firm response definitions (which is not yet the case for PET). Third, U.S. and international cancer management guidelines for treatment monitoring do not yet routinely include PET imaging.
It is the responsibility of the international imaging community to agree on response criteria so oncologists can learn to work with them and accept them.
These considerations are more complicated for radiation therapy response assessments. Fewer well-designed studies have been conducted and inflammatory responses early in treatment render response assessment more difficult. Large multicenter trials are needed to determine the role of PET imaging for radiation planning and for assessing tumor responses to radiation treatment.
Importantly, this can be accomplished early in the course of therapy when there is still an opportunity to change the patient management strategy. This is relevant since many chemo- and chemo/radiation treatments are only marginally effective, are associated with severe side effects and also can be very expensive. Early identification of treatment responses would thus enable referring physicians to optimize and individualize cancer treatments.
Reliable early response assessments have been demonstrated in lung cancer, lymphoma, breast cancer, esophageal cancer and colorectal cancer, among others. Previous evidence has shown that responding tumors are characterized by early reductions in FDG uptake by approximately 30 percent (for instance, after a single cycle of chemotherapy) and by approximately 60 percent at the end of treatment. Remarkably, these changes are seen across most tumors and across various types of chemotherapy. These observations are not limited to patients who undergo cytotoxic treatments but also are seen in those who receive cytostatic therapies.
These “thresholds” are consistent with the EORTC guidelines dating back more than 10 years and with the recently published PERCIST criteria. There are, however, limitations to applying these thresholds. Nevertheless, there are substantially more data to support the clinical use of these criteria when compared with the CT-based response criteria.
This prompts the question: Why is the adoption of the PET-based approach so slow? First, RECIST has been used for decades and practice patterns are difficult to change. Second, RECIST, while inaccurate, provides firm response definitions (which is not yet the case for PET). Third, U.S. and international cancer management guidelines for treatment monitoring do not yet routinely include PET imaging.
It is the responsibility of the international imaging community to agree on response criteria so oncologists can learn to work with them and accept them.
These considerations are more complicated for radiation therapy response assessments. Fewer well-designed studies have been conducted and inflammatory responses early in treatment render response assessment more difficult. Large multicenter trials are needed to determine the role of PET imaging for radiation planning and for assessing tumor responses to radiation treatment.