Evaluation of Quantitative Imaging Methods for Ibritumomab Tiuxetan Dosimetry Using a Population of Phantoms Having Realistic Variations in Anatomy and Uptake
Bin He and Eric C. Frey
Estimating the organ residence times is an essential part of patient-specific dosimetry in targeted radionuclide therapy (TRT). Quantitative imaging methods for TRT are often evaluated using a single physical or simulated phantom but are applied to population of patients with variability in anatomy, biodistribution, and biokinetics. To provide a more relevant evaluation, we have thus developed a population of phantoms with realistic variations and applied it to the evaluation of quantitative methods both to find the best method and to demonstrate the effects these variations.
METHODS AND MATERIALS:
Using whole-body scans and
SPECT/CT images, we measured the organ shapes and time-activity curves of
In-111 ibritumomab tiuxetan in dosimetrically important organs in 10 patients
undergoing a high dose therapy regimen. Based on these measurements, we
created a 3D NCAT-based phantom population. SPECT and planar data at
realistic count levels were then simulated using previously validated
The mean errors in the residence time estimates for all the organs were <4.7%, <13.8%, <6.0%, <15.1%, and 5-122% for pure QSPECT, pure QPlanar, hybrid QPlanar/QSPECT, hybrid CPlanar/QSPECT, and pure CPlanar, respectively. The standard deviations of the errors for all the organs over all the phantoms were <5.5%, <2.4%, <5.3%, < 24.1%, <86.5%, respectively.
The processing methods differed both in terms of their average accuracy and the variation of the accuracy over the population of phantoms. This demonstrates the importance of using phantom population in evaluating image processing methods. QPlanar or hybrid QPlanar/QSPECT method had means and standard deviations of accuracy that approached those of pure QSPECT while providing simplified image acquisition protocols and thus maybe more clinically practical.
NIH R01 grant, "Quantitative SPECT for Targeted Radionuclide Therapy, " PI: EC Frey, 12/1/05-11/30/10