[Analysis of positioning errors in head and neck cancers during radiotherapy assisted by the 6D treatment couch and image-guided radiation therapy].

Objective: To evaluate the intra-fraction and inter-fraction positional deviations in head and neck tumor patients undergoing intensity-modulated radiation therapy (IMRT) guided by cone-beam CT (CBCT), as well as the correction capability and stability of the HexaPOD evo RT 6D couch in addressing these deviations.

Methods: From May 2019 to April 2022, 59 consecutive patients with head and neck tumors were enrolled at the Department of Radiation Oncology, Peking University Third Hospital.Using the Elekta AXESSE image-guided stereotactic treatment system, a pre-treatment CBCT scan was performed, followed by bone window mode registration with the planning reference images.Deviations were corrected automatically or manually on the 6D couch, followed by a second CBCT scan for confirmation of the deviation correction.Positional errors in translation (X, Y, Z directions) and rotation (Rx, Ry, Rz directions) were recorded before and after correction, and intra-fraction and inter-fraction positional errors were analyzed.

Results: Positional error data before and after correction of the 6D couch were successfully obtained and corrected online in 506 CBCT scans.The maximum positional errors before and after correction were 0.90 cm to 0.04 cm (X direction), 1.74 cm to 0.09 cm (Y direction), 1.80 cm to 0.09 cm (Z direction), and 2.90° to 0.14°(Rx direction), 3.00° to 0.15°(Ry direction), 3.00° to 0.15°(Rz direction), respectively.The mean absolute values of translational (X, Y, Z directions) and rotational (Rx, Ry, Rz directions) errors significantly decreased after online correction, from 0.18 cm, 0.22 cm, 0.25 cm, and 0.82°, 1.11°, 0.73° to 0.01 cm, 0.01 cm, 0.01 cm, and 0.04°, 0.06°, 0.04°(all P values < 0.001).After correction, the frequencies of translational errors less than 0.10 cm in the X, Y, Z directions were 99.60%, 98.62%, and 95.45%, respectively, and the frequencies of rotational errors less than 0.2° were all above 99.80%.

Conclusion: Online correction combined with CBCT and the 6D couch significantly reduces both translational and rotational positional errors in patients undergoing head and neck radiation therapy, greatly enhancing the precision of treatment.