Correlation of ADC on DWI and SUV max on PET/CT in primary rectal cancer: a preliminary experience

Abstract

PURPOSE: Diffusion weighted imaging (DWI) is an emerging, whereas PET/CT an established tool for tumor assessment. Tumors often demonstrate decreased apparent diffusion coefficient (ADC) on DWI, and increased standard uptake value (SUV) on FDG-PET/CT. The aim of this study was to assess the relationship between ADC and SUV in primary rectal cancer. METHOD AND MATERIALS: From Nov 08 to Apr 09, 16 consecutive patients (10 men, 6 women; age 55-88 years) with pathologically proven rectal cancer and having undergone both MRI and PET/CT were included in this study. All MRs were performed on a 3T scanner (Achieva, Philips). Routine T1, T2, DWI and contrast-enhanced sequences were obtained. Axial pelvic DWI was obtained by single-shot EPI with STIR fat-suppression and slice-selection gradient reversal technique (TR/TE/TI=7779/47/260ms, matrix 188×151, FOV 40×32 cm, b-value=0 and 1000 s/mm2, slice thickness 5mm). ROIs were manually drawn along contours of the tumor on each slice of ADC maps covering the entire tumor. ADC values were calculated by Image J software (NIH, US). ADCmean was defined as average ADC value for all voxels in each tumor, and ADCmin as the lowest ADC value among all voxels in each tumor. All PET/CT exams (Discovery VCT, GE) were performed within 1 week of MRI. A 3D ROI was placed over the entire tumor on Advanced Workstation (GE) to calculate SUVmax. Maximum diameter of the tumor was measured on both MRI (M_D) and PET/CT (P_D). Relationship between ADC and SUVmax values was assessed by pearsons correlation test. RESULTS: ADCmean and ADCmin for all tumors were 0.96±0.23 and 0.37±0.19 (10-3mm2/s) respectively. SUVmax values were 10.55±6.13. M_D values were 5.78±2.19 cm and P_D 6.11±2.12 cm. Statistically significant negative correlation was found between ADCmin and SUVmax (r=-0.57, p=0.02), and ADCmean and SUVmax (r=-0.65, p=0.006). M_D was significantly correlated with P_D (r=0.49, p=0.02). CONCLUSION: Our preliminary results showed that both ADCmin and ADCmean of the primary rectal cancer are inversely correlated with SUVmax, which has been shown to correlate with tumor aggressiveness and treatment response in many malignancies. CLINICAL RELEVANCE/APPLICATION: ADC values may be potential surrogate biomarkers for detection, characterization, prognostication and monitoring treatment response of rectal cancer.