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

ABSTRACT

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.