Whole-body SPECT/CT with CZT system significantly cuts scan time for metastases detection in prostate cancer

Samuli Arvola from Turku University Hospital and the University of Turku in Kiinamyllynkatu Turku, Finland, and colleagues aimed to investigate the effects of energy window width, acquisition time, and matrix size on the diagnostic performance, quantitation, and image quality of whole-body 99mTc-HMDP SPECT/CT in the staging of primary metastasis of prostate cancer.

They found that the technique reduced total acquisition time from 40 minutes to as low as 16 minutes without any loss of diagnostic performance. Shorter acquisition times could help clinicians to increase accurate whole-body SPECT imaging use in these patients.

Whole-body bone SPECT/CT is reported to be more accurate than computed tomography (CT) and standard planar bone scintigraphy for detecting bone metastases in cancer patients. Still, its clinical use is limited partly due to the shortage of fast acquisition protocols. Current recommendations suggest an acquisition time of at least 40 minutes for whole-body SPECT/CT. However, this guidance was written before developing general-purpose digital CZT (cadmium-zinc-telluride) systems, which allow optimization of acquisition protocols, including imaging time.

For the study, 30 patients with prostate cancer underwent 99mTc-HMDP SPECT/CT from the top of the head to the mid-thigh through a Discovery NM/CT 670 CZT system with 15% energy window width, 50-min acquisition time, list-mode acquisition, and 128 × 128 matrix size.

The authors resampled the acquired list-mode data to produce sets with shorter acquisition times of 16, 20, 26, 32, 38, and 41 min, narrower energy windows of 4, 6, 8, and 10% and a larger size of the matrix, 256 × 256. Three experienced nuclear medicine physicians did the qualitative evaluation of the images, and quantitative evaluation was done by lesion contrast, noise, and SUV measurements. Diagnostic performance was assessed from the readings of two experienced nuclear medicine physicians concerning patient-, region-, and lesion-level sensitivity and specificity.

The authors reported the following findings:

• The originally acquired images were shown to have the lowest noise and best qualitative image quality. However, the acquisition time could be decreased to 38 min, the matrix size increased to 256 × 256, and the energy window narrowed to 8%, with still acceptable qualitative image quality.
• Changes in acquisition parameters did not affect lesion contrast and SUVs.
• Acquisition time reduction did not affect the diagnostic performance, as specificity, sensitivity, and accuracy, and there was no remarkable difference in the area under the receiver-operating characteristic curve between the 50-min and reduced acquisition time images.
• Two readers' average patient-level sensitivities were respectively 92, 88, 96, and 100% for the 32-, 50-, 16-, and 26- min images, and the corresponding specificities were 84, 78, 78, and 84%.
• Two readers' average region-level sensitivities were respectively 58, 55, 56, and 59% for the 32-, 50-, 16-, and 26-min images, and the corresponding specificities were 98, 95, 95, and 96%.
• The number of equivocal lesions is inclined to increase with the decrease in the acquisition time.

"For metastasis staging of high-risk prostate cancer patients, whole-body 99mTc-HMDP SPECT/CT can be obtained utilizing a general-purpose CZT system in less than 20 min without any loss in diagnostic performance," the authors conclude.

Reference:

Arvola, S., Seppänen, M., Timonen, KL et al. Detection of prostate cancer bone metastases with fast whole-body 99mTc-HMDP SPECT/CT using a general-purpose CZT system. EJNMMI Phys 9, 85 (2022). https://doi.org/10.1186/s40658-022-00517-4