Effect of Respiratory Motion on Kidney Volume Determination for Application in Targeted Radionuclide Therapy

Ziel/Aim:

In targeted radionuclide therapies energy dose to kidneys is proportional to area under the time-activity-curve (TAC) and inversely proportional to the kidneys' volume.

SPECT and CT images from multimodal SPECT/CT are often used for sampling the TAC and for determining the kidneys' mass. It is known that the kidneys are perturbed by respiratory motion. If the respective CT subsystem is not able to achieve the necessary scanning speed for breath-hold CT, motion will be present during the scan. This could potentially lead to erroneous volume determination and thus incorrect dosimetry.

The aim of this study was to assess differences in kidney volume determination between free-breathing (FB) and breath-hold (BH) CT acquisitions and to determine corresponding consequences for dosimetry.

Methodik/Methods:

In 16 patients, BH-CT (Siemens Biograph mCT, 40 CT detector slices or equivalent), as well as FB-CT (Siemens Symbia T2, 2 detector slices) were acquired. The time difference between acquisitions was 68 ± 48 days (1 – 147). Volumes of left and right kidneys (in total 32 kidneys) were independently determined by manual CT segmentation. BH- CT was considered as reference. Inter- and intra-reader variability was analyzed.

Ergebnisse/Results:

The average volume difference between BH- and FB-CT was 9.1 ± 6.1% (range 1.8 – 22.0%, p < 0.001), and 11.7 ± 9.8% (2.9 – 43.4%, p < 0.001), for left and right kidneys, respectively. 18 and 14 datasets had higher and lower volumes, respectively, in BH versus FB acquisitions. The difference in measured volume was strongly correlated between left and right kidney (Pearson's r = 0.73, p < 0.001). Intra- and inter-reader variability were 1.8 ± 1.3% and 1.4 ± 0.9%, respectively.

Schlussfolgerungen/Conclusions:

Determination of kidney volume based on FB-CT examinations results in significant deviations when compared to BH- CT. Thus, depending on the respiratory movement relative to the patient table motion during CT acquisition, the volume and energy dose may be either over- or under-estimated.