Design and Fabrication of Kidney Phantoms for Internal Radiation Dosimetry Using 3D Printing Technology

Currently, the validation of multimodal quantitative imaging and absorbed dose measurements is impeded by the lack of suitable, commercially available anthropomorphic phantoms of variable sizes and shapes. To demonstrate the potential of 3-dimensional (3D) printing techniques for quantitative SPECT/CT imaging, a set of kidney dosimetry phantoms and their spherical counterparts was designed and manufactured with a fused-deposition-modeling 3D printer. Nuclide-dependent SPECT/CT calibration factors were determined to assess the accuracy of quantitative imaging for internal renal dosimetry.

A set of 4 single-compartment kidney phantoms with filling volumes between 8 and 123 mL was designed on the basis of the outer kidney dimensions provided by MIRD pamphlet 19. After the phantoms had been printed, SPECT/CT acquisitions of 3 radionuclides (^99mTc, ¹⁷⁷Lu, and ¹³¹I) were obtained and calibration constants determined for each radionuclide-volume combination. A set of additionally manufactured spheres matching the kidney volumes was also examined to assess the influence of phantom shape and size on the calibration constants.

A set of refillable, waterproof, and chemically stable kidneys and spheres was successfully manufactured. Average calibration factors for ^99mTc, ¹⁷⁷Lu, and ¹³¹I were obtained in a large source measured in air. For the largest phantom (122.9 mL), the volumes of interest had to be enlarged by 1.2 mm for ^99mTc, 2.5 mm for ¹⁷⁷Lu, and 4.9 mm for ¹³¹I in all directions to obtain calibration factors comparable to the reference. Although partial-volume effects were observed for decreasing phantom volumes (percentage difference of up to 9.8% for the smallest volume [8.6 mL]), the difference between corresponding sphere-kidney pairs was small (<1.1% for all volumes).

3D printing is a promising prototyping technique for geometry-specific calibration of SPECT/CT systems. Although the underlying radionuclide and the related collimator have a major influence on the calibration, no relevant differences between kidney-shaped and spherically shaped uniform-activity phantoms were observed. With comparably low costs and submillimeter resolution, 3D printing techniques hold the potential for manufacturing individualized anthropomorphic phantoms in many clinical applications in nuclear medicine.