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

The\r\ndisadvantage of visualizing tomography by slices is that an important attribute\r\nof the object, its volume, is not easily perceived or measured. In oncology\r\nthis creates a problem, which is addressed here: if early detection and\r\nresponse to treatment are an important prognostic element, then volume is important.\r\nThe literature has proposed surrogates to volume derived from measures on\r\nslices, but geometrically they are not well founded. Actual volume analysis is\r\nnot complex, and the proposed method applies equally well to organs as to\r\ntumors. Volume based measures are more sensitive than individual SUV values, of\r\nwhich the commonly most used is the maximum Standardized Uptake Value (SUVm). If the tumor volume is\r\ndefined, it can be replaced by the total tumor SUV (SUVt). If the\r\nmetric for change is the ratio after/(before + after), in the patient\r\npopulation analyzed here, the SUVm metric averages 0.132 for\r\nresponse and 0.662 for progression, the total SUVt range is 0.069 to\r\n0.734. In contrast to SUVt, SUVm is based on a weak\r\nsampling method since it is based on the value of a single voxel of more than\r\n10 million.