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.
ABSTRACT
Objective To explore the methods, dosimetric features and short-term effects of partial breast irradiation carried out by three-dimensional external-beam irradiation (3DCPBI) assisted by active breathing control (ABC) . Methods Computed tomography (CT) simulation assisted by active breathing control (ABC) was carried out for each patient and intended to get CT images in condition of 75% deepest inspiration named moderate deep inspiration breath hold (mDIBH). The extent labeled by the silver slips located in the cavity was delineated as gross target volume (GTV) , GTV plus the margin of 15 mm was defined as planning target volume (PTV). 6 MV X-ray was selected as the radiation source and noncoplanar radiation with four three-dimensional conformal fields was used, the described dose was 34 Gy /10f/5d. The volume of GTV, PTV, the affected whole breast, and the percentage of PTV accounted for the affected whole breast , the percentages of PTV included by 100% , 95% and 90% isodose curve, the percentage of volume of the affected breast irradiated by 34. 0, 27. 2, 20. 4, 13. 6 and 6. 8 Gy , and Dmean,D5,V20 of the lungs and heart were calculated respectively. Acute radiation skin response was recorded and the cosmetic effect of the breast after radiotherapy were appraised, with the local tumor control and survival rate followed. Results The mean of volume ratio of PTV and affected whole breast was 14. 88% ; the mean of the volume covered by 90% isodose curve accounted for 92. 54% of the PTV; the volume irradiated by 34 Gy (100% of described dose) accounted for 17. 23% (mean) of the whole breast and 6. 8 Gy (20% of described dose) for 46. 11% , in other words, the volume covered by 20% of described dose was less than 50% of the whole breast. The Dmean, D5, V20 for the affected lateral lung were 1.97, 9. 25 Gy and 1. 58% , it was 0.20, 0. 87 Gy , and 0% for the unaffected lateral lung. The Dmean,D5, V20 for the heart was 0.65 Gy , 2. 82 Gy , and 0. 85%. Zero grade of acute radiation skin reaction was seen in 14 patients and gradel in 3 patients and there was not equal to or more than grade 2 of skin reaction for all the patients. Cosmetic effect were appeci-ated and satisfaction defined as excellent or good appearance of the irradiated breasts for all the patients. No recurrence of local tumor for all of the patients followed for one year. Therefore, the cosmetic result of 1 yr. follow - up was 100% and no recurence was found after 1 yr. follow - up. The 1-year tumor-free survival rate were all 100%. Conclusions For selected patients with early breast cancer after breast-conservative surgery, 3DCPBI assisted by ABC is feasible, however, the selection criteria for the patients, technique protocol and dose fractionation of 3DCPBI and its influence on late cosmetic effect, local tumor control and survival need to be continuously explored and observed in the future.