FDG-PET Imaging and Assessment of Tumor Dose Response (SF2) Distribution

Abstract

To derive tumor cell survival fraction after 2 Gy (SF2) distribution from multiple FDG-PET images obtained during the early weeks of radiotherapy, and evaluate the predictability of SF2 distribution on tumor local failure and recurrent location. FDG-PET/CT images with PET image voxel size of 4 x 4 x 4 mm3 obtained at the pre, weekly and 3/6 months post chemo-radiation treatment for each of 18 HN cancer patients were used for the study. Four of the 18 patients had biopsy proven local failure (22.2%) with the median follow-up time 22.2 (7.5 ∼ 43.3) months. All weekly and post-treatment PET/CT images of each patient were registered voxel by voxel to the pre-treatment planning PET/CT image. Tumor dose response marker, SF2(v), for each tumor voxel v was derived using the linear regression on the logarithm of the first 4 weekly tumor metabolic ratios defined as lnTMRi(v) = ln(SUVi(v)/SUV0(v)), i = 1 to 4. Sensitivity and specificity of SF2-Volume parameters on the prediction of local tumor control and failure were calculated. The relationship between a locally recurrent tumor volume and radio-resistant tumor volume was evaluated. The locally recurrent tumor volume was defined as the iso-SUV volume formed using the %SUVmax on the post-treatment PET image, while the radio-resistant tumor volume was created using the tumor voxels with SF2 > 0.9. The inter- and intra-tumor heterogeneities of SF2 distribution were large with the individual mean from 0.56 to 0.89, and the individual STD from 0.08 to 0.16. All failures had either large mean SF2 or large STD. Sensitivity and specificity, as well as the accuracy, of using V(SF2 > x) to predict treatment local failure were listed in Table 1. Tumor sub-volume with SF2 > 0.9 shows highly predictability on tumor local recurrence after the standard chemo-radiotherapy. In addition, Tumor local recurrent volume (defined using the 70, 80, or 90% of the Post-SUVmax) always contains the radio-resistant tumor voxels (Table 1). Tumor voxel dose response SF2 can be derived using multiple FDG-PET imaging obtained during the early weeks of radiation treatment. Distribution of SF2 has significant predictability power on tumor local failure, and the recurrent location. It can be used as the objective function to target radio-resistant tumor cells.Abstract 1062; Table 1Tumor Volume(SF2>x)V(SF2>0.9)V(SF2>1.0)V(SF2>1.1)Sensitivity0.751.01.0Specificity1.01.01.0Accuracy0.941.01.0AUC0.961.01.0P-value0.0030.0020.002Optimal Cutoff (cc)4.620.960.14Locally Recurrent Volume (LRV)(CC)70% Post-SUVmax 1.09 ∼ 2.8280% Post-SUVmax 0.58 ∼ 1.1590% Post-SUVmax 0.2 ∼ 0.45Radio-Resistant Volume in LRV(CC)0.7 ∼ 1.340.38 ∼ 0.70.19 ∼ 0.38 Open table in a new tab