Comparison of positioning accuracy of different registration methods and dosimetric analysis of adaptive radiotherapy for breast cancer after breast conserving surgery

BACKGROUND: This study explores the effect of different registration methods on the placement accuracy and dosimetric analysis of adaptive radiation therapy (ART) after breast conserving surgery for breast cancer, based on cone-beam computed tomography (CBCT). METHODS: Thirty breast cancer patients, who underwent breast conserving surgery, were divided into three groups, with 10 patients in each group: automatic grayscale registration (group A), automatic bony marker registration (group B), and automatic grayscale registration combined with manual bony marker registration (group C). Three registration methods were conducted before the first radiotherapy, and once a week under the guidance of CBCT. The dosimetric comparison was made with the original plan. RESULTS: The X direction was significantly different between groups A and B (P=0.036). The X and Y direction were significantly different between groups A and C (P=0.001, P=0.019). The placement errors were significantly different between groups B and C in the X and Y directions (P<0.001, P=0.003). The ART plan was significantly better than the original plan, in terms of the D(max), D(mean), D90, V90, V100, V95, HI and CI of planning target volume (PTV) (P<0.05). Furthermore, the ART plan was significantly better, in terms of the D(mean), V5, V10, V20 and V30 of the affected lung, the D(mean), V5, V10, V20 and V30 of the double lung, and the D(mean), V5, V10, V20 and V30 of the heart. Moreover, the D(max), V5 and V10 of the contralateral breast were significantly lower than those in the original CT plan (P<0.05). CONCLUSIONS: For the CBCT placement verification after breast conserving surgery, the accuracy and stability of automatic gray-scale registration combined with manual bone markers are better than those of the automatic gray-scale registration and automatic bone marker registration.