Quantitative bremsstrahlung single photon emission computed tomographic imaging: use for volume, activity, and absorbed dose calculations
Abstract
PURPOSE: To perform bremsstrahlung single photon emission computed tomographic (SPECT) imaging using 32P chronic phosphate for volume and activity quantitation to calculate absorbed dose estimates.
METHODS AND MATERIALS: Seven cancer patients enrolled in clinical Phase I therapeutic protocols were injected with 2.5 million particles of macroaggregated albumin, followed by colloidal 32P chromic phosphate by direct interstitial injection into the tumor-bearing region under computed tomographic (CT) guidance. SPECT images were obtained in these patients. The patient body contour was defined through the use of two externally placed Compton backscatter 99mTc sources. A computer algorithm was written to facilitate region-of-interest volume and activity determination on the reconstructed SPECT slices based on a fixed threshold method. Three sequential SPECT studies were acquired in two of these patients, to determine the accuracy of activity quantitation for bremsstrahlung SPECT studies using Chang's postprocessing method of attenuation compensation with a computer-generated body contour based on the Compton backscatter sources, and an experimentally measured effective linear attenuation coefficient for 32P. The serial data in these two patients were used to calculate absorbed dose estimates.
RESULTS: The 99mTc backscatter sources enabled the patient body outline to be clearly visualized in all the transaxial reconstructed slices and did not contribute significant counts to the…
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