早期乳腺癌保乳术后全乳放疗中瘤床体积变化的CT评价

Repeated computed tomography scanning in assessing the change of tumor bed volume during whole breast irradiation in early-stage breast cancer after breast conservative surgery

目的 用重复定位CT评价早期乳腺癌保乳术后放疗中瘤床体积变化规律,分析不同CT上进行瘤床加量计划的剂量学差异.方法 2008-2009年共收集早期乳腺癌保乳术后放疗患者16例,放疗均采用全乳放疗和瘤床加量.患者均接受了3次CT扫描,分别为放疗前（CT1,常规全乳放疗计划CT）、放疗中（CT2）、瘤床加量前（CT3）.在3次CT上勾画瘤床.在CT1和CT3上进行三维适形瘤床加量计划并分析剂量体积直方图.结果 CT1、CT2、CT3瘤床平均体积分别为49.5、25.6、22.2 cm3（F=5.63,P=0.007）,CT1的＞CT2（q=0.03,P=0.010）和CT3的（q=0.01,P=0.004）,CT3与CT2的相似（q=1.00,P=0.333）.CT3总体积平均下降43.4%,其中下降＞20%的占88%（14例）、＞50%的占38%（6例）.CT1、CT3上患侧乳腺内接受100%处方剂量的平均体积分别为183.5、144.5 cm3（t=3.06,P=0.008）.结论 早期乳腺癌保乳术后放疗患者放疗中瘤床体积以放疗后的早期变化显著,在瘤床加量前重新CT扫描进行三维适形瘤床加量计划是合理的.

Objective To determine the change of tumor bed volume during whole breast irradiation by repeated computed tomography scanning and to analyze the dosimetric impact of boost-planning on different CT images. Methods From July 2008 to Jan 2009, sixteen patients with early-stage breast cancer underwent breast conservative surgery （BCS） were enrolled in the study. All patients received whole breast irradiation and tumor bed boost, no adjuvant chemotherapy was given. Two additional CT scans were acquired in addition to the planning CT （ CT1 ）, one in the course of radiotherapy （ CT2 ） and the other before the boost （CT3）. Tumor beds were contoured in all CT images. Three-dimensional conformal radiotherapy planning for tumor bed boost was done on CT1 and CT3 respectively. Results The mean tumor bed volume on CT1, CT2 and CT3 were 49.5 cm3, 25.6 cm3 and 22. 2 cm3 （ F = 5. 63, P = 0. 007 ）,respectively. Further analysis found statistically significant difference between CT1 and CT2 （ q = 0. 03, P =0. 010）, CT1 and CT3 （ q = 0. 01, P = 0. 004）, but not between CT2 and CT3 （ q = 1.00, P = 0. 333 ）. The average reduction of tumor bed volume from CT1 to CT3 was 43.4%. A reduction of 20% or above was found in 88% of the patients （ n = 14）, 50% or above in 38% of the patients （n = 6）. In the boost-planning, the volume of the ipsilateral breast receiving 100% prescribed dose （V100%） on CT1 and CT3 was 183.5 cm3 and 144. 5 cm3, respectively （ t = 3.06, P = 0. 008 ）. Conclusions Volume of tumor bed is dynamically reduced in the course of whole breast irradiation after BCS, with more important reduction in the early weeks after the beginning of irradiation. A second CT scan before tumor bed boost is warranted.