Multisequence MR-generated sCT is promising for HNC MR-only RT: A comprehensive evaluation of previously developed sCT generation networks

Purpose To verify the feasibility of our in-house developed multisequence magnetic resonance (MR)-generated synthetic computed tomography (sCT) for accurate dose calculation and fractional positioning for head and neck MR-only radiation therapy (RT). Methods Forty-five patients with nasopharyngeal carcinoma were retrospectively studied. By applying our previously in-house developed network, a patient's sCT can rapidly be generated with respect to feeding the sole T1 image, T1C image, T1DixonC image, T2 image, and their combination (five pipelines in total). A k(5)-fold strategy was implemented during model establishment. Dose recalculation was performed for each pipeline generation to attain a dosimetric feasibility evaluation. Fractional positioning evaluation was performed by calculating the digitally reconstructed radiograph (DRR) of the sCT and planning CT and their offset to the portal image. Results The dose mean absolute error values were (0.47 +/- 0.16)%, (0.48 +/- 0.15)% (p < 0.05), (0.50 +/- 0.16)% (p < 0.05), (0.50 +/- 0.15)% (p < 0.05), and (0.45 +/- 0.16)% (p < 0.05) for the T1, T1C, T1Dixon C, T2, and 4-channel generated sCT to the prescription dose, respectively. The 4-channel-generated sCT outperforms any other single-sequence pipeline. Among the single-sequence MR imaging-generated sCTs, the T1-generated sCT shows the most accurate HU image quality and provides a reliable dose result. Quantified positioning errors with calculation of the difference to the planning CT offsets are (-0.26 +/- 0.50) mm, (-0.58 +/- 0.52) mm (p < 0.05), (-0.27 +/- 0.57) mm (p > 0.05), (-0.31 +/- 0.44) mm (p > 0.05), and (-0.19 +/- 0.37) mm (p > 0.05) at LNG and (0.34 +/- 0.53) mm, (0.48 +/- 0.56) mm (p > 0.05), (0.55 +/- 0.56) mm (p > 0.05), (0.37 +/- 0.61) mm (p > 0.05), and (0.24 +/- 0.43) mm (p > 0.05) at LAT of the anterior-posterior direction for the five pipelines. Conclusion Multisequence MR-generated sCT allows for accurate dose calculation and fractional positioning for head and neck MR-only RT.