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 / 中华放射肿瘤学杂志

ABSTRACT

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.