AAPM: CT perfusion shows early tumor vascular changes after radiotherapy
PHILADELPHIA—CT perfusion assessment of rectal cancer after hypofractionated radiotherapy correlated well with FDG-PET assessment and showed an increased tumor perfusion. Researchers suggest that the increased vascularity could improve the bioavailability of cytotoxic agents in rectal tumors, often administered early after radiotherapy treatment, according to a poster presentation at the annual meeting of the American Association of Physicists in Medicine (AAPM).
Guido Lammering, MD, PhD, and colleagues from the department of radiation oncology at Maastricht University Medical Center in the Netherlands, studied 30 patients diagnosed with rectal cancer. All patients underwent FDG-PET and perfusion CT imaging prior to the start of radiotherapy treatment.
Researchers quantified tumor perfusion with three parameters: transfer constant, fractional extravascular-extracellular space and fractional plasma volume. On the PET images, the tumor was delineated using automated standardized uptake value (SUV) thresholding.
Lammering and colleagues found a significantly increased transfer constant after radiotherapy. In addition, the median transfer constant values were significantly higher for tumor than for muscle tissue on both the pre- and post-scans.
In contrast, they found no differences between tumor and muscle tissues before and after radiotherapy for fractional extravascular-extracellular space and fractional plasma volume.
The mean and maximum transfer constant values had positive correlations to the corresponding SUVs. These also had positive correlations within tumor subregions.
"Highly perfused rectal tumors presented with higher FDG uptake levels when compared to relatively low-perfused tumors," he said.
The Dutch group had been the first to demonstrate that perfusion CT correlated well with dynamic contrast-enhanced MRI, which was published June 1 in the International Journal of Radiation Oncology Biology Physics. Results were similar in that transfer constant values correlated well with MRI, while the other two parameters— fractional extravascular-extracellular space and fractional plasma volume—did not.
CT perfusion can serve as an alternative modality to MRI for evaluation of tumor angiogenesis, concluded Lammering, who noted that the study suggests that PET/CT can be used in this patient population to determine early effects of hypofractionated radiotherapy.
Guido Lammering, MD, PhD, and colleagues from the department of radiation oncology at Maastricht University Medical Center in the Netherlands, studied 30 patients diagnosed with rectal cancer. All patients underwent FDG-PET and perfusion CT imaging prior to the start of radiotherapy treatment.
Researchers quantified tumor perfusion with three parameters: transfer constant, fractional extravascular-extracellular space and fractional plasma volume. On the PET images, the tumor was delineated using automated standardized uptake value (SUV) thresholding.
Lammering and colleagues found a significantly increased transfer constant after radiotherapy. In addition, the median transfer constant values were significantly higher for tumor than for muscle tissue on both the pre- and post-scans.
In contrast, they found no differences between tumor and muscle tissues before and after radiotherapy for fractional extravascular-extracellular space and fractional plasma volume.
The mean and maximum transfer constant values had positive correlations to the corresponding SUVs. These also had positive correlations within tumor subregions.
"Highly perfused rectal tumors presented with higher FDG uptake levels when compared to relatively low-perfused tumors," he said.
The Dutch group had been the first to demonstrate that perfusion CT correlated well with dynamic contrast-enhanced MRI, which was published June 1 in the International Journal of Radiation Oncology Biology Physics. Results were similar in that transfer constant values correlated well with MRI, while the other two parameters— fractional extravascular-extracellular space and fractional plasma volume—did not.
CT perfusion can serve as an alternative modality to MRI for evaluation of tumor angiogenesis, concluded Lammering, who noted that the study suggests that PET/CT can be used in this patient population to determine early effects of hypofractionated radiotherapy.