Metrics to Evaluate PET Response to Therapy Based on 3D Analysis

The disadvantage of visualizing tomography by slices is that an important attribute of the object, its volume, is not easily perceived or measured. In oncology this creates a problem, which is addressed here: if early detection and response to treatment are an important prognostic element, then volume is important. The literature has proposed surrogates to volume derived from measures on slices, but geometrically they are not well founded. Actual volume analysis is not complex, and the proposed method applies equally well to organs as to tumors. Volume based measures are more sensitive than individual SUV values, of which the commonly most used is the maximum Standardized Uptake Value (SUVm). If the tumor volume is defined, it can be replaced by the total tumor SUV (SUVt). If the metric for change is the ratio after/(before + after), in the patient population analyzed here, the SUVm metric averages 0.132 for response and 0.662 for progression, the total SUVt range is 0.069 to 0.734. In contrast to SUVt, SUVm is based on a weak sampling method since it is based on the value of a single voxel of more than 10 million.