Different methods for the detection of small changes in uptake between single-photon emission computed tomography...

This study was undertaken to evaluate different methods for the detection of small changes in uptake between single-photon emission computed tomography (SPECT) examinations in the same individual. No standard exists for making digital evaluations at single-photon examinations. For this purpose, we employed a patient cohort from a previous study assessing the response to neoadjuvant chemotherapy for breast cancer using Tc-hexakis-2-methoxyisobutylisonitrile (Tc-sestamibi).

The tumour uptake in 29 women with locally advanced breast cancer was examined using Tc-sestamibi and SPECT before neoadjuvant chemotherapy and, on average, 19 days after one chemotherapy cycle. The histology of the finally resected tumour confirmed a therapeutic response. Different assessments of the uptake, various levels of background activity subtraction and different reference tissues for relative activity calculations were used. The tumour uptake and activity of the reference tissues were also related to the administered activity.

Different definitions of tumour activity had little influence. Relating the tumour uptake to a large portion of the abdomen, as well as visual evaluation, showed a therapeutic response. Comparison with the administered activity showed that the apparent responses were due to an increased activity of the reference tissues. Referring the tumour uptake to the administered activity truly depicted a therapeutic response.

A critical attitude is necessary when making digital evaluations at SPECT. Digital data may seem more relevant than they really are. Relative comparisons may be unreliable. It may be necessary to develop standardized methods for this purpose.