Setup Errors And Effectiveness Of Optical Laser 3D Surface Imaging System(Sentinel^TM) In Postoperative Radiotherapy Of Breast Cancer

Objectives:To compare the setup accuracy of optical surface imaging by the SentinelTM system with cone-beam computerized tomography(CBCT)imaging currently used in our clinic for patients received breast conservative surgery(BCS).Methods:Two optical surface scans were acquired before and immediately after couch movement correction.The correlation between the setup errors as determined by the initial optical surface scan and CBCT was analyzed.The deviation of the second optical surface scan from the reference planning CT was considered an estimate for the residual errors for the new method for patient setup correction.The consequences in terms for necessary planning target volume(PTV)margins for treatment sessions without setup correction applied.Results:We analyzed 390 scans in 76 patients treated for early stage breast cancer.The correlation coefficient r of CBCT errors(CE)and SentinelTM errors before the couch movement(SE-before)in every dimension were between 0.541～0.796,indicating significant correlations,and the p-values were less than 0.001.The systemic errors and random errors for CE and SE-before were comparable between the two alignment methods with the differences in X,Y,and Z directions by 0.13mm and 0.53mm,0.28mm and 0.34mm,and 0.34mm and 0.17mm,respectively.The rotational errors were also very similar for the two methods with the differences less than 0.2°.Accordingly,the anisotropic PTV margins derived from SentinelTM were different from the CBCT data by 0.63mm,0.33mm,and 0.56mm in X,Y,and Z directions,respectively.The impact of rotational errors to the PTV margins are expected to be included.The PTV margins derived from the residual errors based on the SentinelTM surface imaging scanned after the couch movement were reduced to 4.49mm,4.85mm,3.67mm in X,Y,and Z directions,respectively.Compared with SentinelTM setup errors,the systemic errors and random errors for CBCT residual errors are all less than the SentinelTM errors in the six directions.The PTV margins derived from the residual errors based on the CBCT scanned after the couch movement were reduced,and are all less than 5mm in X,Y,and Z directions.Conclusions:Optical surface imaging provides a convenient method for improving the setup accuracy for breast cancer patient without unnecessary imaging dose.