Planning comparison of intensity modulated radiation therapy delivered with 2 tangential fields versus 3-dimensional conformal radiotherapy for cardiac sparing in women with left-sided breast cancer.

Purpose: In women with unfavorable thoracic anatomy undergoing left breast radiation therapy (RT) after breast-conserving surgery, a significant volume of the heart may receive high-dose radiation, which has been shown previously to be associated with increased late cardiac morbidity and mortality. Use of intensity modulated radiation therapy (IMRT) has been proposed to reduce cardiac dose in these patients. We compared cardiac exposure from IMRT delivered from 2 opposed fields and 3-dimensional conformal radiation therapy (3DCRT) plans employing simple heart blocks.

Methods And Materials: Fourteen patients with left-sided breast cancer treated with breast-conserving surgery and RT were identified to have unfavorable cardiac anatomy, defined as maximum heart depth (MHD) ≥1.0 cm within the unblocked opposed tangential fields. 3DCRT plans utilized dynamic wedges, segments, and custom heart blocks designed by the treating physician. Tangent IMRT plans were optimized to reduce cardiac dose while maintaining planning target volume (PTV) coverage equal to that achieved with the 3DCRT plan. We generated tangential field plans with complete heart block (CHB) or no heart block (NHB) for comparison. Plans were normalized to deliver 46 Gy to the PTV. Dose to the heart, PTV, and lumpectomy cavity were compared.

Results: Mean MHD was 1.44 cm (1.0-1.86 cm). There was no significant difference in PTV receiving >95% of the prescription dose between 3DCRT and IMRT, as intended. Mean V30 to the heart was 0% for CHB plans, 1.7% for 3DCRT plans, 1.8% for IMRT plans, and 3.3% for NHB plans, respectively. There was no significant difference in heart V30 for 3DCRT and IMRT plans (P = .8). IMRT plans delivered 256 total monitor units compared with 201 in 3DCRT plans (P < .01).

Conclusions: Inverse-planned tangent IMRT does not reduce high-dose radiation to the heart compared with 3DCRT, incorporating a simple heart block in women with left-sided cancer and unfavorable cardiac anatomy when PTV coverage was equalized for both plans. In select patients with early-stage breast cancer and unfavorable thoracic anatomy, 3DCRT with heart block may be sufficient to adequately protect the heart from high-dose radiation.