Comparison of normal tissue dose with three-dimensional conformal techniques for breast cancer irradiation including the internal mammary nodes.

PURPOSE: To compare the Para Mixed technique for irradiation of the internal mammary nodes (IMN) with three commonly used strategies, by analyzing the dose to the heart and other organs at risk.

METHODS AND MATERIALS: Four different three-dimensional conformal dose plans were created for 30 breast cancer patients. The IMN were enclosed with the Para Mixed technique by a widened mediolateral tangent photon beam and an anterior electron beam, with the Patched technique by an anterior electron beam, with the Standard technique by an anterior photon and electron beam, and with the PWT technique by partially wide tangents. All techniques were optimized for conformality and produced equally adequate target coverage.

RESULTS: Heart dose was lowest with the Para Mixed and Patched technique for all patients and with the PWT technique for right-sided treatment only. Lung dose was highest with the PWT, lowest with the Patched, and intermediate with the Para Mixed and Standard techniques. Skin dose was highest with the Patched, lowest with the PWT, and intermediate with the Para Mixed and the Standard techniques. The Para Mixed technique resulted in a 13-Gy lower dose in an overlap area, and the PWT technique was the only technique that incorporated considerable volumes of the contralateral breast.

CONCLUSION: The Para Mixed technique yielded the overall best results. No other technique resulted in a lower heart dose. Lung and skin were equally spared instead of one of them being compromised, and the contralateral breast was avoided.