Study of match methods in cone beam computed tomography online correction for postoperative radiotherapy in liver cancer patients

Abstract

Objective To compare five different match methods in cone beam computed tomography (CBCT) online correction for postoperative radiotherapy in liver cancer patients.Methods Twelve postoperative liver cancer patients were included in the study.Metal markers were placed in tumor beds.They underwent CBCT 214 times before and after radiotherapy.Five different match methods,including fiducial marker clipbox using bone automatic match (fiducial marker match),routine big clipbox using bone automatic match (routine bone match),routine big clipbox using grey value automatic match (routine grey value match),vertebral body clipbox using bone automatic match (vertebral body match),and diaphragmatic dome clipbox using grey value automatic match (diaphragmatic dome match),were used in off-line analysis.The results of fiducial marker match were compared with those of other four match methods using paired t-test and Pearson correlation analysis.Results The CBCT 214 times data analysis results showed that compared with fiducial marker match,the difference of errors in left-right (x),superior-nferior (y) and anterior-posterior(z) directions of the other four methods was statistically significant (t =-13.48 -14.56,P ＜ 0.05) except y direction in routine bone match and x direction in vertebral body match (t =0.75,P =0.452 ;t =-0.97,P =0.333).The correlation analysis results showed good correlation between routine grey value match and fiducial marker match in y direction (r =0.852,P =0.000),with poor correlation in other comparisons (r =0.367-0.777,P =0.000 for all comparisons).Compared with the results from fiducial marker match,84.1％-93.0％ of the results from other four match methods have an absolute error larger than 2 mm in at least one of x,y,and z directions,and 65.9％-79.9％ of the match results have an absolute error larger than 3 mm in at least one of the three directions.Conclusions If there are metal markers in the target volume,fiducial marker match should be used in CBCT online correction for postoperative radiotherapy in patients with liver cancer; other match methods used in the absence of metal markers will produce some errors,so appropriate increase in planning target volume margin is needed in this case. Key words: Liver neoplasm/radiotherapy; Tomography, X-ray computed, cone-beam; Image match