Miyako Myojin, Presenter: Nothing to Disclose

To know the clinical implication of tumor bed boost after the tangential irradiation following breast conserving surgery (BCS) to decrease the rate of local control ( LC).To certificate the indication criteria for boost radiotherapy.

A consecutive series of 302 cases treated with BCS and radiotherapy (RT) of the conserved breast were analyzed for this article. Two hundred sixty-cases of the all have been enrolled to our prospective cohort study which is definitely controlled by boost criteria concerned with surgical extent, pathological information and tumor size. The other 41 cases were treated with whole breast irradiation alone without tumor bed boost ignoring these criteria. These patients group was defined as control.Tumor margin free was defined as >5mm in this series. Boost criteria were as follows; 1. When quadrantectomy is selected, boost is necessary in the margin positive cases. 2. When lumpectomy is selected, boost is applied in any of the following pathological features; (a) margin positive, (b) intraductal component positive, (c) tumor multiplicity, and (d) intraductal spread from invasive ductal lesion. 3. Boost dose is 15Gy /6F/1.5wks and boost beam is 9~12 MeV electron as a general rule. 4. When lumpectomy is selected for T2 cases, 10Gy boost is necessary at least. 5. When residual tumor is considered as a nest, boost technique is permitted to change to brachytherapy.

All of the cases were observed from 46 to 191 months (median 70) after BCS. The over all survival rate was 98.0% at 5 years and 94.7% at 10 years. The mean age was 50 years (=40: 57 cases, 41~50: 104 cases, 51~60: 79cases, 61~: 61cases).T stages were T0: 3cases, T1: 212cases, and N stage were N0: 245 cases, N1: 51 cases and unknown: 4 cases, respectively. There was no significant difference in age distribution, T & N stages, observation time, over all survival between 260 cases of the cohort group and 41 cases of the control group, respectively .Consequently, 87 cases were judged as no boost from the pathological criteria , 126 cases as 15Gy boost, 5 cases as brachytherapy. Forty two cases were resulted in 10Gy boost. The distributions of the pathological features in the groups were as follows; multiple tumors: 29:2, positive margin: 105:9, intraductal component: 121:26, intraductal spread 146:24 in the cohort group vs. the control group, respectively. There was a significant difference in LC rate between the two groups ( cohort group: 99.6% at 5 years and 98.3% at 10 years , control group: 92.4% at 5 years and 92.4% at 10 years). Two local recurrences were observed at 36 and 89 months in the cohort group (crude: 2/260) and 3 local recurrences at 32.5, 34.6 and 41.5 months in the control group (crude: 3/41). Any of the prognostic factors such as surgical margin, other pathological features , and age distribution did not significantly affect the results of LC except for the observance of boost criteria. Four of the 5 local recurrent cases had not treated with boost.

We have experienced a good result on LC by boost irradiation in conservative treatment of Stage I-II breast cancer, observing definite pathological boost criteria prospectively

Myojin, M, A Result of Cohort Study on Boost Irradiation in the Conservative Treatment of Stage I-II Breast Cancer: From the Pathological Point of View.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/6001691.html