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.
Humans ; Cone-Beam Computed Tomography ; Head and Neck Neoplasms/diagnostic imaging* ; Radiotherapy, Image-Guided/methods* ; Radiotherapy, Intensity-Modulated/methods* ; Patient Positioning/methods* ; Radiotherapy Planning, Computer-Assisted/methods* ; Male ; Radiotherapy Setup Errors/prevention & control* ; Female

Some patients who have neck tumor but cannot tolerate the thermoplastic immobilization may be supported by simple cushions, and are marked on the neck skin during CT simulation. We therefore set 5 mm as the spinal cord-planning risk volume margin in the intensity-modulated radiotherapy plans in our Centre. Cone beam CT (CBCT) scans were acquired for three times, and matched with the simulation CT images in each radiotherapy. The mean and the standard deviation of the individual, the root mean-square and the standard deviation of the individual were calculated. The matched results of the third CBCT were used to calculate the spinal cord- planning risk volume margin. The results showed that the interfraction error was significantly reduced and the intrafraction error was stable by CBCT guiding. CBCT and 5 mm spinal cord-planning organ is feasible and safe without threatening volume margin to high dose radiotherapy for the patients with neck tumor and not able to tolerate thermoplastic immobilization.
Cone-Beam Computed Tomography ; Head and Neck Neoplasms ; diagnostic imaging ; radiotherapy ; Humans ; Patient Positioning ; methods ; Radiotherapy Planning, Computer-Assisted ; methods ; Radiotherapy Setup Errors ; prevention & control ; Radiotherapy, Image-Guided ; methods ; Radiotherapy, Intensity-Modulated ; instrumentation ; methods

Cone-beam CT (CBCT) of Elekta can be used to analyze the setup errors in intensity modulated radiotherapy. A total of 240 patients with head and neck cancer were chosen in the period from October, 2009 to October, 2010. Their CBCT images were obtained after initial setup, and registered to the planning CT images, and then the setup errors on translational directions (X, Y, Z) and on rotational directions (U, V, W) were obtained and analyzed. The results showed that the setup errors on translational directions in Y-axis and Z-axis were larger than in X-axis, and the setup errors on rotational directions in Y-axis was much more obvious than those on the other two directions, which should be taken care during the patient daily setup. It may be concluded that the CBCT system can improve the precision for radiotherapy.
Cone-Beam Computed Tomography ; methods ; Head and Neck Neoplasms ; diagnostic imaging ; radiotherapy ; Humans ; Radiotherapy Setup Errors ; prevention & control ; statistics & numerical data ; Radiotherapy, Intensity-Modulated