Comparison of R2 Values Using the Spin Echo-Multi Echo and T2 Mapping Methods for Polymer Gel Dosimeter with Radiotherapy

Abstract

Purpose: This study aimed to clarify the effect of R2 and ΔR2 values from spin echo (SE)-multi echo and T2 mapping methods on magnetic resonance imaging (MRI) of polymer gel dosimeters.Methods: The polymer gel dosimeters were irradiated with 0–20 Gy of 6 MV X-rays, and images were acquired using the SE-multi echo technique in 3.0 T MRI. The R2 and ΔR2 values were calculated using SE-multi echo and T2 mapping methods.Results: The R2 values for the SE-multi echo and T2 mapping methods were 1.76±0.59 (median: 1.44) and 2.73±0.47 (median: 2.46), respectively (P < 0.001). Spearman's rank correlation coefficient was 0.92. The ΔR2 values for the SE-multi echo and T2 mapping methods were 0.46±0.60 (median: 0.04) and 0.34±0.49 (median: 0.02), respectively (P < 0.001). Spearman's rank correlation coefficient was 0.75. The dose-response (Gy-1 s-1) of the SE-multi echo method was higher than that of the T2 mapping method.Conclusion: The effect of R2 and ΔR2 values on MRI of polymer gel dosimeter when comparing the SE-multi echo and T2 mapping methods was clarified. The T2 mapping method can be used when using gel dosimeters with higher dose sensitivity, such as MAGAT, and may be used for evaluation when using PAGAT at high irradiation doses, such as 10 and 20 Gy.

Keywords: T2 mapping, SE-multi echo, R2 value, PAGAT, polymer gel dosimeter