Study subjects comprised 50 consecutive patients with Stage 0?II unilateral breast cancer who underwent breast-conserving surgery, and in whom five or six surgical clips were placed during surgery. All patients were subsequently replanned using three-dimensional conformal radiotherapy (3D-CRT) APBI techniques according to the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-39 and Radiation Therapy Oncology Group (RTOG) 0413 protocol. The beam arrangements included mainly noncoplanar four- or five-field beams using 6-MV photons alone.
Dose-volume histogram (DVH) constraints for normal tissues according to the NSABP/RTOG protocol were satisfied in 39 patients (78 % ). Multivariate analysis revealed that only long craniocaudal clip distance (CCD) was correlated with nonoptimal DVH constraints (p = 0.02), but that pathological T stage, anteroposterior clip distance (APD), site of ipsilateral breast (IB) (right/left), location of the tumor (medial/lateral), and IB reference volume were not. DVH constraints were satisfied in 20 % of patients with a long CCD (?.5 cm) and 92 % of those with a short CCD (p < 0.0001). Median IB reference volume receiving ?0 % of the prescribed dose (IB-V50) of all patients was 49.0 % (range, 31.4-68.6). Multivariate analysis revealed that only a long CCD was correlated with large IB-V50 (p < 0.0001), but other factors were not.
Patients with long CCDs (?.5 cm) might be unsuitable for 3D-CRT APBI because of nonoptimal DVH constraints and large IB-V50.