Room: Exhibit Hall | Forum 5
Purpose: To describe a mathematical method for the analysis of SPECT data from Technetium-99m labeled macroaggregated albumin (99mTc-MAA) for planning the treatment of liver tumors with Ytterbium 90 (90Y) microspheres.
Methods: In preparation for the treatment of liver tumors with 90Y microspheres, 99mTc-MAA is injected into the blood vessel feeding the tumor bed. The patient's liver is scanned using SPECT with the results analyzed using appropriate software (such as Siemens e.soft) so that the value D of the iso-dose surfaces can be plotted as a monotonically decreasing function of the volume V contained within.
Results: If the tumor can be distinguished from the surrounding non-cancerous parenchyma, a log-log plot of D(V) will often display two distinct linear segments smoothly connected within a transition region. The linearity of the segments implies that the iso-dose value of the surface is a function of the volume to a negative power. Typically, within the tumor region, the absolute value of the power is very low, substantially less than 1; in the surrounding region, the absolute value is much higher, typically around 2 (implying a steep descent in the dose with increasing volume). If the tumor is not well isolated and has spread to the entire perfused region, there will not be two distinct linear portions of the curve; there may just be a single gradual curve with no apparent transition.
Conclusion: A log-log plot of D(V), the iso-dose surface value as a function of the volume within can, when the tumor is well isolated, provide a useful estimate of tumor volume which can help with planning tumor treatment with 90Y microspheres. The power law dependence on volume can be interpreted as a dimensionality which may be related to the fractal nature of the tumor vascularity.