Research on CTV-PTV Margin for Pelvic Tumor Based on the Halcyon Accelerator's Guided Mode with 100%Image Guidance
Objective To explore setup errors of clinical target volume to planning target volume(CTV-PTV)margin in pelvic tumor based on Halcyon accelerator's fully guided mode with 100%image guidance.Methods A total of 19 patients with pelvic tumors who underwent intensity modulated radiation therapy on the Halcyon accelerator from January to May 2023 were selected as the study subjects.A total of 900 cone beam CT images were collected,including 300 sets of inter-fractional,post-correction and intra-fractional images for each patient.These images were registered and fused with the planned CT to obtain the three-dimensional vector error,represented by X(left-right),Y(head-foot),and Z(anterior-posterior)directions.Then,the setup errors and their distribution trends were calculated,and the margin of CTV-PTV based on the corrected and intra-fractional setup errors were determined.Results In the X direction,the absolute setup errors between inter-fractional,corrected and intra-fractional were(2.07±1.82),(0.19±0.19),(0.30±0.28)mm respectively.In the Y direction,the absolute setup errors were(3.87±2.67),(0.23±0.31),(0.27±0.23)mm respectively.In the Z direction,the absolute setup errors were(0.72±0.83),(0.20±0.22),(0.30±0.27)mm respectively.All differences were statistically significant(P＜0.05).There were 97%and 96.33%of corrected and intra-fractional set-up errors in the X,Y,Z directions within 1 mm.CTV-PTV margin had been reduced from 6.36 mm to 1.06 mm.Conclusion From the perspective of setup errors,for pelvic tumor treatment based on Halcyon accelerator(100%image guided mode),the CTV-PTV margin is calculated as 1.1 mm based on the corrected and intra-fractional setup errors.Treatment of pelvic tumor patients using the Halcyon accelerator can reduce setup errors,improve the safety and accuracy of targeting the tumor region and organs at risk,reduce the CTV-PTV margin,and minimize the volume of normal tissues involved.
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