[en] Purpose: To perform bremsstrahlung single photon emission computed tomographic (SPECT) imaging using ³²P chromic 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 patient ³²P counts. The calculated activities from the SPECT studies were within 7.8% of the administered ³²P activity. The two calculated patient absorbed doses were 4.2 x 10³ Gy and 5.9 x 10³ Gy for injected activities of 736 MBq and 920 MBq, respectively. Conclusion: We conclude that accurate quantitative bremsstrahlung SPECT imaging, for the case of high contrast well-localized activity distributions, with a commercially available postprocessing attenuation correction algorithm, can be performed in a clinical setting. Entirely SPECT-based measurements can be used to generate absorbed dose estimates