Objective To evaluate the accuracy and reproducibility of AlignRT-guided positioning by comparing two positioning workflows for pelvic tumor radiotherapy,and to further explore the feasibility of using it to replace skin marker alignment.Methods Forty cases of pelvic tumor treated with radiotherapy using Infinity accelerator in Sun Yat-sen University Cancer Center between March 2022 and March 2023 were included in the study,with 20 cases using the skin marker alignment workflow and the other 20 adopting AlignRT-guided positioning workflow.The translational errors(LAT,LNG,VRT)and rotational errors(Yaw,Pitch,Roll)were determined by the registration of pre-treatment cone-beam CT(CBCT)with planned CT.Both CBCT shifts and error offset distributions were analyzed;planning target volume(PTV)margins were calculated;and correlation analyses were conducted among six-dimensional errors,and between body mass index and setup errors.Results The median translational and rotational setup errors of skin marker alignment workflow vs AlignRT-guided positioning workflow were 0.19-0.34 cm vs 0.10-0.15 cm and 0.50°-1.30°vs 0.50°-0.70°,with the maximum offset ranges of 1.20-1.70 cm vs 0.42-0.47 cm and 2.00°-5.50° vs 1.80°-2.00°,respectively.Additionally,for skin marker alignment workflow,inter-fractional errors>0.5 cm and>3° were observed in 23.3%and 9.8%of fractions.The PTV margins of AlignRT-guided positioning workflow were 0.37,0.38 and 0.34 cm in the left-right,superior-inferior and anterior-posterior directions,respectively,which were much smaller than those of skin marker alignment workflow(0.67,1.22 and 0.95 cm).No correlation was found between six-dimensional errors in two positioning workflows.When using AlignRT-guided positioning workflow,the setup errors in LAT,LNG and Pitch directions had low correlations with body mass index.Conclusion In pelvic tumor radiotherapy,AlignRT-guided positioning can reduce translational and rotational errors,achieve precise setup and excellent inter-fractional reproducibility and stability,and replace traditional skin marker alignment while being used in conjunction with CBCT.

Objective To evaluate the accuracy and reproducibility of AlignRT-guided positioning by comparing two positioning workflows for pelvic tumor radiotherapy,and to further explore the feasibility of using it to replace skin marker alignment.Methods Forty cases of pelvic tumor treated with radiotherapy using Infinity accelerator in Sun Yat-sen University Cancer Center between March 2022 and March 2023 were included in the study,with 20 cases using the skin marker alignment workflow and the other 20 adopting AlignRT-guided positioning workflow.The translational errors(LAT,LNG,VRT)and rotational errors(Yaw,Pitch,Roll)were determined by the registration of pre-treatment cone-beam CT(CBCT)with planned CT.Both CBCT shifts and error offset distributions were analyzed;planning target volume(PTV)margins were calculated;and correlation analyses were conducted among six-dimensional errors,and between body mass index and setup errors.Results The median translational and rotational setup errors of skin marker alignment workflow vs AlignRT-guided positioning workflow were 0.19-0.34 cm vs 0.10-0.15 cm and 0.50°-1.30°vs 0.50°-0.70°,with the maximum offset ranges of 1.20-1.70 cm vs 0.42-0.47 cm and 2.00°-5.50° vs 1.80°-2.00°,respectively.Additionally,for skin marker alignment workflow,inter-fractional errors>0.5 cm and>3° were observed in 23.3%and 9.8%of fractions.The PTV margins of AlignRT-guided positioning workflow were 0.37,0.38 and 0.34 cm in the left-right,superior-inferior and anterior-posterior directions,respectively,which were much smaller than those of skin marker alignment workflow(0.67,1.22 and 0.95 cm).No correlation was found between six-dimensional errors in two positioning workflows.When using AlignRT-guided positioning workflow,the setup errors in LAT,LNG and Pitch directions had low correlations with body mass index.Conclusion In pelvic tumor radiotherapy,AlignRT-guided positioning can reduce translational and rotational errors,achieve precise setup and excellent inter-fractional reproducibility and stability,and replace traditional skin marker alignment while being used in conjunction with CBCT.