Analysis of the inter-and intra-fraction setup errors and residual errors during stereotactic radiotherapy for brain metastasis / 中华放射肿瘤学杂志

ABSTRACT

Objective To evaluate the necessity of arc by arc setup verification in patients with brain metastases receiving stereotactic radiotherapy (SRT) by analyzing the inter-and intra-fraction setup errors and residual errors collected from the ExacTrac X-ray portal image.Methods Clinical data of brain metastases patients treated with SRT in the previous two years were retrospectively analyzed.The ExacTrac X-ray setup images were collected after the normal setup procedure.Setup errors were calculated by registering the cranial bony structures of the ExacTrac X-ray setup images to that of the digitally reconstructed setup images.The inter-and intra-fraction setup errors and residual errors were statistically analyzed.Results Seventy-five patients from 116 lesions received 337 cycles of SRT of the head.The inter-and intra-fraction translational setup errors in the x,y and z directions were (0.93±0.86) mm and (0.15±0.59) mm;(1.83± 1.27) mm and (0.25±0.73) mm;(0.96±0.80) mm and (0.14±0.56) mm,respectively.The inter-and intra-fraction rotational setup errors in the x,y,z directions were (0.65°± 0.62°) and (0.19°± 0.40°);(0.97°±0.94°) and (0.13°± 0.25°);(0.92°± 0.71°) and (0.10°± 0.29°),respectively.The residual translational setup errors in the x,y,z directions were (0.06±0.23) mm,(0.08±0.24) mm and (0.08±0.22)mm,and (0.12°± 0.27°),(0.09°± 0.18°) and (0.06°± 0.19°) for the residual rotational setup errors,respectively.For a reference setup error threshold of 0.7 mm/0.7°,99.1％ of the SRT exceeded the threshold and required setup correction.For 1 006 non-coplanar arcs,rotating the treatment couch from 0° to the treatment angle made 66.4％ of arcs exceed the threshold and require at least once setup correction.Conclusions During SRT for brain metastasis,the inter-and intra-fraction setup errors should be emphasized.It is necessary to perform arc by arc setup error verification.