Background: Several methods have been reported for accelerated partial breast irradiation (APBI), but in Japan, there are few facilities where brachytherapy or intra-operative radiotherapy is available. Japanese women have smaller physiques than American women in general. Thus, we developed external beam plans for APBI using computed tomography (CT) data of Japanese patients, to investigate whether APBI using three-dimensional conformal radiation therapy is safely applicable for Japanese women, while verifying the dose distributions.
Methods: We used CT data from six Japanese patients with early breast cancer, which were obtained in routine clinical practice during whole breast irradiation (WBI) after wide excision, and made 32 APBI plans according to the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-39 and the Radiation Therapy Oncology Group (RTOG) 0413 protocol, which compared APBI with WBI. We then investigated the compliance to the dose constraints of the protocol.
Results: None of 16 plans for the medial regions met the dose constraints regardless of laterality of the breast. The major reason was overdosage to the contralateral breast. Thirteen of 16 plans (81%) for the lateral regions met the dose constraints. The remaining three plans (19%) did not meet the dose limitation of the uninvolved normal breast, suggesting that a large ratio of the target to the breast was problematic.
Conclusions: In Japanese women, patients with a laterally located small tumor can be candidates for APBI using three-dimensional conformal radiation therapy.