Apparent diffusion coefficient (ADC) accuracy and geometric performance of rsEPI and ssEPI were compared using phantoms, and in vivo, involving 8 patients prior to MR-guided brachytherapy for locally advanced cervical cancer, and 19 patients with prostate cancer planned for tumor-targeted radiotherapy. Global and local deviations in geometric performance were tested using Dice Similarity Coefficients (DC) and Hausdorff Distances (HD).
In cervix patients, DC increased from 0.76 ± 0.14 to 0.91 ± 0.05 for the high risk clinical target volume, and 0.62 ± 0.26 to 0.85 ± 0.08 for the gross tumor target volume. Tumors in the peripheral zone of the prostate gland were partly projected erroneously outside of the posterior anatomic boundary of the gland by 3.1 ± 1.6 mm in 11 of 19 patients using ADC-ssEPI but not with ADC-rsEPI.
Both cervix and prostate ssEPI are prone to clinically relevant geometric distortions at 3 T. rsEPI provides improved geometric performance without post-processing.