Study On Clinical Application Of ICBCT-guided Volumetric Modulated Arc Therapy For Pelvic Tumor

In recent years,the increasing prevalence and mortality of pelvic tumors have become a global public health problem.Volumetric modulated arc therapy（VMAT）,as the treatment method for medically inoperable pelvic tumors,has no significant difference from the effect of surgery.With the development of image-guided radiation therapy（IGRT）and the upgrade of equipment,setup error analysis in the process of radiotherapy has become a research hotspot.The iterative k V cone-beam CT（ICBCT）is a novel image-guided radiotherapy technique,which can provides technical support for improving the accuracy and precision of radiotherapy positioning for pelvic tumors,effectively reducing the exposure range of normal tissues,and formulating a reasonable external boundary of internal target volume（ITV）radiotherapy for pelvic tumor.Purposes1.To study the setup errors of image-guided radiotherapy in patients with pelvic tumor in the X-axis（left and right）,Y-axis（head and foot）and Z-axis（abdominal and back）and its influencing factors.2.To calculate the planned target volume（PTV）margins for pelvic tumor radiotherapy.Methods1.The VMAT radiotherapy guided by the airborne ICBCT of Halcyon 2.0 linear accelerator was used to conduct localization,target volume delineation and plan design for pelvic tumor patients,and the setup errors of X-axis（left and right）,Y-axis（head and foot）and Z-axis（abdominal and back）were obtained.2.According to a margin recipe derived by Van Herk: 2.5Σ+0.7σ,we calculated the PTV margins in different directions,so that 90% of patients’ clinical target volume（CTV）were irradiated with more than 95% of the prescribed dose.ResultsThe results of 434 ICBCT setup errors of 34 patients with pelvic tumor were as follows: X-axis 0.00（-0.20,0.30）cm,Y-axis 0.10（-0.20,0.50）cm,Z-axis 0.00（-0.10,0.13）cm.The results of 234 True Beam CBCT setup errors of 19 patients with pelvic tumor were as follows: X-axis-0.08（-0.40,0.21）cm,Y-axis 0.04（-0.21,0.33）cm,Z-axis 0.07（-0.11,0.30）cm,Pitch 0.50（-0.40,1.33）°,Roll 0.40（-0.30,1.10）°,Rtn0.00（-0.90,0.70）°,and compared with ICBCT,the setup errors of X-axis and Z-axis were statistically significant（P < 0.01）.Among them,the results of 237 ICBCT setup errors of 18 patients with cervical cancer were as follows: X-axis 0.00（-0.30,0.25）cm,Y-axis-0.10（-0.30,0.30）cm,Z-axis 0.00（-0.10,0.20）cm.The results of 178 ICBCT setup errors of 13 patients with colorectal cancer were as follows: X-axis 0.10（-0.10,0.30）cm,Y-axis 0.30（0.00,0.50）cm and Z-axis 0.00（-0.20,0.10）cm.The setup errors have a significant difference in X-axis,Y-axis,Z-axis between cervical cancer group and colorectal cancer group（P < 0.001）.The results of setup errors of 2patients with endometrial cancer were as follows: X-axis 0.05（-0.18,0.35）cm,Y-axis-0.20（-0.38,0.35）cm,Z-axis-0.15（-0.28,0.28）cm.The setup errors of one patient with vaginal cancer treated by ICBCT-guided radiotherapy were as follows: X-axis0.10（-0.50,0.30）cm,Y-axis-0.80（-1.10,0.00）cm,Z-axis 0.00（0.00,0.10）cm.In addition,the setup errors of ICBCT-guided radiotherapy in Y-axis were significantly negatively correlated with age of patients,while the setup errors of ICBCT-guided radiotherapy in X-axis,Z-axis and True Beam CBCT-guided radiotherapy in six dimensions were not significantly correlated with age of patients（P > 0.05）.The PTV margins obtained by ICBCT-guided radiotherapy for pelvic tumor was:10.08 mm in X-axis,12.94 mm in Y-axis and 4.67 mm in Z-axis.The PTV margins obtained by ICBCT-guided radiotherapy for cervical cancer,colorectal cancer were as follows: X-axis（12.24 mm,7.13mm）,Y-axis（13.71 mm,10.31mm）,Z-axis（3.92 mm,4.69mm）.True Beam CBCT-guided radiotherapy of pelvic tumor resulted in the PTV margins: X-axis 12.91 mm,Y-axis 8.24 mm,Z-axis 9.89 mm,Pitch 3.65°,Roll 2.57°and Rtn 3.02°,respectively.Conclusion1.The setup errors of ICBCT-guided radiotherapy for pelvic tumor patients were the largest in Y-axis（head and foot）,followed by X-axis（left and right）and Z-axis（abdominal and back）.The setup errors in Y-axis were significantly negatively correlated with the age of patients.2.The setup errors between ICBCT and True Beam CBCT are significantly different in X-axis and Z-axis,and the positioning of ICBCT-guided VMAT radiotherapy for pelvic tumor may be more accurate than True Beam CBCT.3.The setup errors of ICBCT-guided VMAT radiotherapy for patients with cervical cancer and colorectal cancer are significantly different in X,Y and Z axes,suggesting that the setup errors may be related to the type of disease or treatment sites.4.ICBCT-guided VMAT radiotherapy for patients with pelvic tumor should fully consider the existence of setup errors and the difference of treatment sites,and develop the individual PTV margins.