Evaluation of irradiated heart volumes in stage I breast cancer patients treated with postoperative adjuvant radiotherapy.

PURPOSE: To quantify the proportion of heart volumes that received at least 25 Gy with tangential photon fields in patients with left-sided stage I (T1 NOMO) breast cancer treated with breast-conserving surgery. METHODS AND MATERIALS: The dose planning of 100 consecutive patients was reviewed. All were irradiated with tangential photon fields that covered the left breast only. A three-dimensional computed tomographic (CT)-based dose planning was made for each patient. The prescribed dose to the tumor was 50 Gy. For each patient, the proportion of the heart included in the 50% isodose was determined from the cumulative dose-volume histogram (DVH). The same volume determination was made for the left-sided breast cancer patients treated with tangential fields during the first Stockholm Breast Cancer Trial.
RESULTS: The mean irradiated heart volume that received at least 25 Gy was 5.7% (SD = 4.5%) for the whole group and 11.9% (SD = 3.7%) in those with the highest volumes. The mean irradiated heart volume included in the 50% isodose for patients in the Stockholm Trial was 25% (SD = 11.9%).
CONCLUSION: In this study, the majority of patients with left-sided T1NOMO breast cancer did not receive irradiation to substantial heart volumes. However, in 6% of all studied patients, the proportion of irradiated heart volume was close to the irradiated heart volumes with one of the treatment techniques used in the Stockholm Trial for patients with left-sided tumors. That technique has been associated with significantly increased cardiac mortality during long-term follow-up evaluation in a previous study. The CT-based three-dimensional treatment-planning system (TMS) represents a valuable tool in identifying such patients; thus, treatment may be conformed to reduce the irradiated heart volume.